The Iowa Scaled Engineering ProtoThrottle has many ardent users who typically use the throttle to control locomotives with track-powered DCC. This post shows you how to implement using this throttle for Dead Rail (battery power, radio control) with ProMiniAir, Airwire, Tam Valley Depot DRS-1, S-Cab, and Gwire Receivers that can receive commands from ProMiniAir Transmitter integrated with a WiFi-equipped CommandStation (available on eBay by using the “ProMiniAir” search string).
My thanks to Colin Camarillo for the idea.
Implementation
Implementation is straightforward and smooth. You will need the following components:
ProtoThrottle Receiver (ProtoThrottle Receiver for ESU CabControl, JMRI WiFi Throttle, and Digitrax LNWI): available here.
ProMiniAir Transmitter/WCS (ProMiniAir Receiver integrated with a WiFi-equipped EX-CommandStation): available here.
Compatible Receivers are:
ProMiniAir
Airwire CONVRTR, G-3, and G-4
Tam Valley Depot DRS-1
S-Cab
Gwire
First, power up the ProtoThrottle and set the locomotive’s address, e.g., 1648, along with the illustrated functions. See the ProtoThrottle’s User Manual for detailed operation and configuration details.
The ProtoThrottle has been set to the locomotive’s address with the illustrated functions.
The PrototThrottle Receiver has a config.txt file that is available on a file system once connected to a PC. You edit this file with your favorite text editor, modifying the following entries for operation with a DCCEX system:
The”123456“is replaced by the actual value shown on the CommandStation’s OLED display. Save the file. Disconnect the USB cable from the PC and plug it into the USB power block.
Set up the configuration file for the Iowa Scale Engineering Receiver for WiFi Systems for a WiFi-equipped EX-CommandStation. Plug the Receiver’s USB cable into a computer and edit the Receiver’s config.txt file. Note that the settings are for the WiFi-equipped EX-CommandStation.
The photo below shows that the ProtoThrottle Receiver is connected to the EX-CommandStation after the USB power is connected.
The Iowa Scale Engineering Receiver shows connections to the WiFI-equipped EX-CommandStation.
The photo below shows that the EX-CommandStation is successfully sending DCC commands to the ProMiniAir Transmitter (note the “Msg Ad: 1648”) on the small OLED display connected to the ProMiniAir Transmitter).
The WiFi-equipped EX-CommandStation is integrated with a ProMiniAir Transmitter. Note that the PMA’s message address (“Msg Ad: 1648”) matches that sent by the ProtoThrottle.
Demonstration
The video below is a demonstration of the following arrangement: [ProtoThrottle] ===Xbee===> [ProtoThrottle Receiver] ===WiFi===> [WiFi-equipped EX-CommandStation] —wired—> [ProMiniAir Transmitter] ===Airwire Channels===> [ProMiniAir, Airwire, Tam Valley Depot, S-Cab, Gwire Receivers] —wired—> [DCC decoder].
Demonstration video: The O Scale H-8 Allegheny has a ProMiniAir Receiver with a 13A Cytron Amplifier connected to a Zimo MS990K decoder with a Heinz Daeppen Allegheny sound file. The sound from recordings of the actual locomotive is impressive.
Wrap Up
The setup of the ProtoThrottle and its Receiver was simple, and it took just a few seconds to edit the ProtoThrottle’s config.txt file so the ProtoThrottle Receiver could communicate with the WiFi-equipped EX-CommandStation. Communication among all of the components was immediately established when power was applied.
So, there you have it: the ProtoThrottle can be used for Dead Rail control with ProMiniAir, Airwire, Tam Valley Depot DRS-1, S-Cab, and Gwire Receivers by using the ProtoThrottle Receiver in conjunction with a ProMiniAir Transmitter integrated with a WiFi-equipped EX-CommandStation.
As some of you may know from my previous postings or other sources, if you try “raw” transmission of DCC from standard DCC throttles, such as with the Tam Valley Depot DRS1 transmitter, to Airwire receivers, you probably won’t get consistent control – I didn’t. This failure set me on the road to devise the ProMiniAir transmitter that would work with CVP Airwire receivers using DCC generated by standard DCC throttles, including the superb “open-source” WiFi-equipped EX-CommandStation created by the folks at DCC-ex.com. Of course, the ProMiniAir receiver is fully-compatible with Airwire throttles.
My web research and discussions with fellow dead-railers led me to believe you might solve the compatibility problem by providing frequent DCC “Idle” messages. Once the dust settled on the ProMiniAir firmware we made available on our GitHub site, the ProMiniAir transmitter worked pretty well with Airwire receivers! Besides CVP Airwire transmitters, the ProMiniAir transmitter is the only currently-manufactured transmitter that works with Airwire receivers.
After this success, we have worked hard to ensure that the ProMiniAir transmitter (and receiver) are compatible with multiple product lines, including CVP Airwire, Tam Valley Depot DRS1 transmitters and receivers, Gwire transmitters and receivers (available but no longer manufactured), Stanton Cab transmitters and receivers, and the no longer manufactured NCE D13DRJ.
OK, you may ask, what’s the point of this post? Well, I’d like to share some further research on the source of the CVP receiver’s incompatibility and its consequences on updates for the ProMiniAir transmitter/receiver firmware.
Further Investigations
OK, I based our initial success in making the ProMiniAir transmitter compatible with CVP Airwire receivers on observing how well the ProMiniAir worked with Airwire receivers. Yep, numerous inserted DCC IDLE messages from the ProMiniAir transmitter seemed to keep the Airwire receivers reasonably “happy,” responding to throttle speed/direction commands and function activation.
However, sometimes the Airwire receiver seemed a bit slow to respond to function activation… And some customers (who are hopefully still friends) sometimes noted this slow response. Could this be improved?
Still, I hadn’t analyzed what an Airwire throttle was sending in detail, so I purchased a simple logic analyzer from Amazon to look at the actual DCC transmitted by an Airwire throttle. I also needed the “pulseview” software from sigrok.org and a DCC decoder add-on. To properly analyze DCC, I modified the add-on and will make it available on our GitHub site.
The figure below is what I observed by firing up my original ProMiniAir transmitter integrated with a WiFi-equipped EX-CommandStation, and using the iOS WiThrottle app to send throttle commands to a ProMiniAir receiver. The figure below shows the “raw” digital output from the ProMiniAir receiver’s transceiver.
The raw DCC data received by a ProMiniAir receiver from a ProMiniAir transmitter integrated with a WiFi-equipped EX-CommandStation
The waveform is what you would expect. A “one” end packet bit from the previous DCC packet and then a series of 15 “one” preamble bits followed by a “zero” packet start bit that signals to the decoder that a DCC command is coming. I observed no significant or consistent DCC “errors” in the collected data.
The preamble to a packet consists of a sequence of “1” bits. A digital decoder must not accept as a valid, any preamble that has less then 10 complete one bits, or require for proper reception of a packet with more than 12 complete one bits. A command station must send a minimum of 14 full preamble bits.
The data below is what I observed by firing up an Airwire T5000 transmitter and looking at the “raw” digital output pin from the transceiver (radio) on the ProMiniAir receiver.
The raw DCC data received by a ProMiniAir receiver from an Airwire T5000 throttle
Well, well. Now we see an NMRA-permissible (see line 121 of NMRA Standard S 9.2) but non-DCC transition pair, called a “cutout,” with a 1/2 “one” and 1/2 “zero” pair after a valid “one” end packet bit and before a very long (30 “one” bits) preamble. If you try to send shorter preambles, say 15 “one” bits, the Airwire receiver will NOT work consistently despite the NMRA standard stating that a decoder must not require more than 12 complete “one” bits in the preamble. So, the Airwire receiver is placing a non-standard requirement for a “long” preamble of “one” bits before it will operate consistently.
Timing of a 1/2 “one” and 1/2 “zero” cutout
While reviewing the DCC sent from an Airwire throttle, there were NOT an unusual number of DCC “Idle” messages sent by the Airwire transmitter. But, by sending tons of short (3 bytes) DCC “Idle” messages, the ProMiniAir transmitter was sending just enough “one” bits to keep the Airwire receiver functional. I am not privy to the details of Airwire’s receiver firmware, so my success was based purely on empirical observation without underlying “insider” knowledge.
So what? With this knowledge, I felt it essential to make some ProMiniAir firmware changes.
Firmware Changes to the ProMiniAir Transmitter
Based on this new information, to improve compatibility with Airwire receivers, we have modified the ProMiniAir transmitter’s firmware to ensure a 1/2 “one” followed by a 1/2 “zero” cutout comes after the end packet “one” bit, and before at least 30 “one” bits are in the preamble. This change is NOT harmful to other wireless receivers, including the ProMiniAir receiver. The ProMiniAir transmitter and receiver still insert DCC “Idle” messages when possible to keep decoders “happy” while waiting for valid DCC messages from the throttle.
Along with these firmware changes, which will be made available on our GitHub site, you can set the number of “one” bits in the preamble by going into OPS mode at address 9900 (transmitter) or 9901 (receiver) by setting the value of CV242. If you set the value of CV242 to 0, the firmware sets the number of preamble bits to a “reasonable” value of 16 (receiver) or the number of preamble bits the throttle sent (transmitter). If you set CV242 to less than 12, it will be reset to 12 to ensure decoders are “satisfied” with the number of preamble “one” bits.
You can also change the duration of the cutout’s second 1/2 transition with CV240. By default, a CV240 value of 27 makes the second 1/2 transition a “zero” with a duration of 116us. If you do NOT want a cutout inserted, you can set the CV240 value to 141, which will make the duration equal to that of the cutout’s leading 1/2 “one” (58us), resulting in an output 1/2 “one” and 1/2 “one” pair, simply increasing the number of preamble “one” bits by one.
Example CV240 values to control cutout duration
So, how well do these modifications work for Airwire receivers? It isn’t easy to quantify, but the Airwire receiver’s red data LED remains “on” more consistently with less “flicker,” and the receiver’s DCC output to the decoder contains “cutouts” (with a duration of about five preamble “one” bits) just before the preamble. These characteristics are now very similar to those from an actual Airwire throttle. See the comparison figures below. It’s difficult for me to test the more practical aspects of these improvements, but the decoders continue to operate as I would expect, perhaps with somewhat less time delay. Other users may be able to test under more stressful conditions.
CONVRTR DCC output to the decoder from an Airwire transmitter. The cutout duration does NOT matter to the decoder.CONVRTR DCC output to the decoder from a PMA transmitter with updated firmware. The cutout duration does NOT matter to the decoder.
Conclusion
We now have a better idea why Airwire receivers do not work well with output from a typical, NMRA-conformant DCC throttle sent wirelessly and how to better cope with Airwire receivers’ unique DCC requirements by sending very long DCC preambles, preceded by a 1/2 “one” and 1/2 “zero” cutout.
Raw empiricism often leads you to workable, pragmatic solutions, but a little “looking under the hood” for the “how” and “why” almost always pays dividends. If you own a ProMiniAir transmitter and are not satisfied with its performance with Airwire receivers, don’t hesitate to contact me about how I can provide you with an update to see if your performance will improve.
The new, stand-alone ProMiniAir transmitter integrated with a WiFi-equipped EX-CommandStation
Many model railroaders enjoy using a hand-held throttle or smartphone app that connects to a centralized DCC command station that sends DCC over the tracks to decoder-equipped locomotives, and some “dead-railers” enjoy a similar experience using specialized hand-held transmitters such as the CVP Airwire or Stanton Cab throttles. These dead-rail throttles are expensive and sometimes hard to find due to supply chain problems. Other hand-held dead-rail throttles only support their proprietary receivers and “vendor-lock” users because they have no interoperability with other dead-rail vendors 🙁
On another page, I showed how easy it was to use a smartphone equipped with a “wiThrottle-compliant” app in conjunction with the ProMiniAir transmitter to control your dead-rail locomotive(s) fitted with a variety of receivers such as ProMiniAir, Tam Valley Depot DRS1, CVP Airwire, Stanton Cab, QSI Gwire, and NCE. The downside was that you must invest in a WiFi device for the DCC base station connected to the ProMiniAir transmitter. Many folks pushed back on the additional cost and infrastructure to use their smartphone app for dead-rail control using the ProMiniAir transmitter.
I searched for a way to provide a low-cost way to use your smartphone in conjunction with the ProMiniAir transmitter, and this post shows the low-cost solution that I offer for sale.
The solution: I came across a low-cost way to create a small DCC base station equipped with WiFi at a very active group, DCC-EX, and I will describe how I configured this base station to use a smartphone to control dead-rail locomotives equipped with ProMiniAir, Tam Valley Depot, CVP Airwire, QSI Gwire, NCE, or Stanton Cab receivers.
The wiThrottle-protocol smartphone apps that will work with this solution include (this list is from DCC-EX):
The critical point is that the ProMiniAir transmitter, coupled with the WiFi-equipped EX-CommandStation, is an entirely self-contained solution for $49.99 on eBay (search on eBay with “ProMiniAir” to find this device). All you need to do is apply power and then connect with a smartphone throttle app for mobile control of dead-rail.
If you don’t want to go through the details of the solution, you can jump to the Instructions below.
The Solution
The DCC-EX team has developed an open-source, low-cost DCC controller EX-CommandStation. Here is the DCC-EX team’s description (reprinted from here):
An EX-CommandStation is a simple but powerful, DCC Command Station that you can assemble yourself and which is made using widely available Arduino boards. It supports much of the NMRA Digital Command Control (DCC) standards, including
Simultaneous control of multiple locomotives and their functions
The primary intention of the EX-CommandStation is to receive commands from multiple throttles and send out DCC on tracks. These throttles can be “wired” or “wireless:”
USB
WiFi
Ethernet
Bluetooth
JMRI
With the WiFi-equipped EX-CommandStation, you can use a wiThrottle-protocol smartphone app that connects to the EX-CommandStation via WiFi. Then the EX-CommandStation’s +3.3V logic DCC output is not sent to a “motor shield” to power tracks but instead serves as a direct input to the ProMiniAir transmitter for dead-rail control. It’s that simple; the technique was easy to implement and is low-cost ($49.99 on eBay, instead of paying for a WiFi device that connects to a commercial DCC throttle, a total of over $200).
Instructions for Using the ProMiniAir Transmitter/WiFi-Equipped EX-CommandStation with a Smartphone
What you need:
A smartphone loaded with the wiThrottle-compliant app. See the list above.
A properly configured ProMiniAir Transmitter/WiFi-equipped EX-CommandStation. We provide this.
A locomotive(s) equipped with receivers compatible with the ProMiniAir transmitter, such as:
ProMiniAir receiver
Tam Valley Depot DRS1 receiver
CVP Airwire receiver: CONVRTR 15/25/60, G-3/4
Gwire receiver
Stanton Cab receiver
NCE D13DRJ wireless decoder
Steps:
Plug the USB power into the PMA Tx/WiFi-equipped EX-CommandStation, which turns on the ESP32 WiFi transceiver to broadcast information for your smartphone to pick up, boots up the EX-CommandStation itself, and powers up the ProMiniAir receiver and the OLED displays. You can connect a USB battery pack to the ProMiniAir transmitter/WiFi-equipped EX-Command station for “take it anywhere” capability.
Go to the smartphone’s WiFi settings:
If you have a home router, turn off auto-join, which prevents your smartphone from jumping to your home router rather than the DCC-EX WiFi router.
Select the EX-CommandStation’s WiFi router. The router’s name is “DCCEX_123456,” where “123456” is a unique series of numbers and letters (the “MAC address” of the WiFi transceiver).
When asked for a password, enter “PASS_123456”, where “123456” is the exact string of numbers and letters in the router’s name. You will probably need to enter the password only once since your smartphone will probably remember the password.
The “fiddle factor:” Sometimes, the smartphone will complain it cannot connect to the DCCEX router or that the password is incorrect. Ignore this complaint (assuming you entered the password correctly) and try connecting again. The smartphone will often successfully connect once you select the DCCEX router again.
You might want to turn on the auto-join option for this router so that your smartphone will automatically try to connect once the WiFi-equipped EX-CommandStation is powered up.
Once connected, go to your throttle app:
When asked for WiFI router configuration, set the IP address to “192.168.4.1” and the port to “2560“.
Once your throttle app connects to the EX-CommandStation, you can select your loco(s), etc.
Turn on your dead-rail locomotives, and control them with your smartphone app!
Once finished with the throttle app, you can go back to settings and re-select the auto-join option for your home router.
So here is the “proof of principle” demo. The photo below shows the prototype solution: a low-cost EX-CommandStation with integrated WiFi connected to a ProMiniAir transmitter. The video shows the iOS “Locontrol” app connected to the PMA Tx/EX-CommandStation with WiFi to control a dead-rail locomotive equipped with a ProMiniAir receiver and a DCC decoder that controls loco speed and direction, lighting, sound, and smoke. The Locontrol app is excellent because you can record video while controlling the locomotive.
The solution is a low-cost EX-CommandStation with integrated WiFi connected to a ProMiniAir transmitter. Up to five smartphones with WiFi throttle apps send commands to the WiFi receiver connected to the centralized command station, generating DCC output that the ProMiniAir transmitter sends to onboard locomotive receivers. NOTE: In current versions, Pin 18 instead of Pin 7 is the +5V DCC data connection to the PMA transmitter.Detailed connectionsVideo of using the iOS Locontrol app with the PMA Tx/EX-CommandStation with WiFi to control a dead-rail locomotive equipped with a PMA receiver and DCC decoder
Programming on the Main (PoM) or Service Mode
OK, these smartphone throttle apps are great, but they have a limitation: they can’t currently send commands in PoM (OPS) mode or Service Mode to change the value of configuration variables “CV” in a decoder. This capability is necessary when you need to change the configuration of the ProMiniAir transmitter (whose default DCC address is 9900), such as the wireless channel (CV255 = 0-18) or power level (CV254=1-10). Of course, you might also need to make CV changes to your dead-rail locomotive’s DCC decoder using PoM (OPS) mode, too!
See the DCC-ex.com site for a full list of DCC-EX commands that you can send to the EX-CommandStation and ultimately to the dead-rail locomotives or DCC accessories.
You may NEVER change the ProMiniAir’s configuration, but you might. How to do this?
Solution #1
Both iOS and Android have apps that come to the rescue: TCP/IP to Serial Terminal and Serial WiFi Terminal. The apps provide a wireless connection to the EX-CommandStation to reconfigure the ProMiniAir transmitter (or receiver, for that matter!) or your dead-rail locomotive’s DCC decoder in PoM mode.
Service Mode setting of CVs is also possible. The Service Mode command for changing the CV number CVnum to a value CVval is <W CVnum CVval>. The “W” must be uppercase. Changing the DCC address is even simpler: <W new_address>. Care must be used, since PoM commands will be used by all “listening” receivers, regardless of their DCC address!
So, there you have it, a wireless way to control a WiFi-equipped EX-CommandStation in Programming on the Main (PoM) mode (OPS mode) and Service Mode. While we need these apps to send PoM commands to reconfigure the ProMiniAir transmitter, you can enter any DCC-EX Command! Have fun!
Solution #2
If you have a Windows, macOS, or Linux computer or laptop, you can interact with the WiFi-equipped EX-Command station, including reconfiguring the ProMin Air transmitter. The technique is based on the “curl” program.
What you need:
A Windows, macOS, or Linux computer or laptop.
A WiFI-equipped EX-CommandStation
Steps:
Connect the EX-CommandStation’s USB cable+USB converter to power. This powers up the WiFi-equipped EX-CommandStation and the ProMiniAir transmitter with its LCD.
On your computer, select the DCCEX_123456 wireless router and, if asked, enter the password PASS_123456, where “123456” is a unique string representing the MAC address of the ESP8266 WiFi transceiver integrated with the EX-CommandStation.
On your computer, start up a “terminal” session. A terminal session allows you to type in commands.
Enter the following command curl telnet://192.168.4.1:2560. This opens a simple telnet-protocol connection between the computer and the WiFi-equipped EX-CommandStation at address 192.168.4.1 port 2560, the default EX-CommandStation address and port.
Your command line will now wait for you to enter the text transmitted to the EX-CommandStation! As a test, type in <s> and press RETURN, and you should see a response such as <p0> <iDCC-EX V-4.0.0 / MEGA / PMA_Tx G-a26d988> If using curl on Windows, you may need to press RETURN then ^Z (CONTROL+z) and then RETURN again to “flush” out the response from the EX-CommandStation.
OK! Now let’s change the ProMiniAir transmitter’s channel to “5” by using a PoM (OPS) command (DCC Address: 9900, CV#: 255, CV value: 5): type in <w 9900 255 5> and press ENTER. You will not see a response (sigh), but if you look at the ProMiniAir transmitter’s LCD, you will see the following:
You exit the session by hitting < control>+C.
Pretty simple!
Solution #3
This solution is NOT all wireless but demonstrates how to use the Web-based WebThrottle-EX to control the EX-CommandStation.
What you need:
A computer or laptop
A WiFi-equipped EX-CommandStation
The USB cable that came with your EX-CommandStation
Steps:
Connect the USB cable from the EX-CommandStation to your computer/laptop. This connection provides power and a data link to the PC.
On your computer or laptop’s Chrome web browser, navigate this link: https://dcc-ex.github.io/WebThrottle-EX. An excellent throttle application will start, and the DCC-EX team has excellent instructions for using this application. We will concentrate on our narrow goal: getting OPS mode instructions to the ProMiniAir transmitter.
Select the “Connect DCC++ EX” button to activate the USB serial connection to the EX-CommandStation.
You will see a pull-down menu of USB ports. Select the serial port you think is correct, and if it is, the log window at the bottom will cheer your success. If not, try another USB port from the pull-down list.
Now look at the Debug Console and ensure Debug in “ON.”
In the “Direct Command” entry, type in a “direct” command. In our example, we want to send an OPS mode command (“w” for write) to DCC address 9900 (the PMA transmitter) to change CV 255 (channel selection) to the value of 3 (the channel we want to transmit on): w 9900 255 3.
Press “Send,” and you should see the log window indicating the send. You should also see the PMA Tx’s LCD show a changed value, now with a new channel!
Disconnect the USB cable.
Use your smartphone to connect the ProMiniAir Tx/WiFi-equipped EX-CommandStation as described above.
Have fun controlling the locomotive(s)!
Of course, if you maintain the USB cable connection, you can play with the WebThrottle-EX to control the dead-rail locomotive! The DCC+EX website has excellent instructions for using WebThrottle-EX. The traditional locomotive control capability and the powerful direct control capability are valuable and fun.
An important point: These instructions are ONLY for reconfiguring the ProMiniAir transmitter or changing the CVs in your DCC decoder. Under regular smartphone throttle app use, you do NOT need to connect anything other than the power to the WiFi-equipped EX-CommandStation to activate the ProMiniAir transmitter!
Final Thoughts
While I called this approach for using a smartphone app with the ProMiniAir transmitter a “compromise solution,” if you think about it, with a more centrally-located ProMiniAir transmitter coupled to a small, inexpensive WiFi-equipped DCC base station, you achieve good layout coverage because the base station is acting as an optimally-located “repeater,” potentially reaching more of the layout than your smartphone app. This approach is a valuable “division of labor:” the smartphone gives you the mobility to enjoy different vantages, and the central transmitter covers the layout optimally. So, maybe this approach is better than a “compromise solution,” after all.
Advantage of an optimally-located central transmitter versus a local transmitter.
Typical application. In some cases, such as the Airwire transmitters, the throttle and transmitter are combined. Also, the receiver and amplifier may be integrated, such as for Airwire and Tam Valley Depot receivers. The ProMiniAir transmitter and receiver require a “DCC Converter” or “DCC Amplifier” provided as part of the purchase.
I was inspired to fully develop a wireless DCC transmitter and receiver by two sources: Martin Sant, who runs the BlueRidge Engineering website, and an article by Mark and Vince Buccini titled “Build Your Own Wireless DCC System” that appeared in the April, June, and August 2014 editions of Garden Railways magazine. These back issues are still available.
The Buccinis showed that it was possible to home-build a wireless DCC system. And Martin became a great collaborator who concretely started me with the initial version of the “ProMiniAir” wireless DCC transmitter/receiver hardware and the wireless DCC software for the Pro Mini microcontroller board. I am deeply indebted to these people.
Note: Some photos may show older versions of the ProMiniAir. Also, previous versions of the ProMiniAir receiver and transmitter used 9000/9001 for their DCC address, respectively, which we changed to 9900/9901. Photos and examples may use the now-obsolete addresses.
Update for New Versions of the ProMiniAir Transmitter and Reciever
Please see this post on an important update on the ProMiniAir transmitter. It is now completely stand-alone; just plug in power and use your cell phone app to control your locomotive.
The new completely stand-alone ProMiniAir transmitter. Just plug in power, use your smartphone app to connect to the WiFI-equipped EX-CommandStation, and control your dead-rail locomotive.
The ProMiniAir transmitter and receiver have been significantly reduced in size: 1.1″ x 0.8″, making it possible to mount the ProMiniAir receiver and a tiny DCC amplifier in tighter spaces and some HO locomotives.
The new ProMiniAir receiver and small amplifier (3.6A)
Feature Comparisons
My goal for offering the ProMiniAir receiver/transmitter is to provide those interested in “dead-rail” (radio control, battery power of a model railroad locomotive) inexpensive wireless, DCC compatible transmitters and receivers for radio-control of model railroad locomotives in the US/Canadian 915MHz ISM band – the same band and protocol as used by Tam Valley Depot (TVD), CVP Airwire, NCE/QSI Gwire, and Stanton Cab. Also, you can operate the ProMiniAir transmitter and receiver in the European ISM band at 869.85MHz, and we have verified interoperability with Tam Valley Depot European DRS1 transmitters and receivers.
A note about channels: modern CVP Airwire transmitters and receivers can all operate in the Airwire channels designated 0-16 using current Anaren AIR transceiver chips. Older wireless transmitters and receivers from Tam Valley Depot and Stanton Cab used the Linx ES series transmitter or receiver chip that only operated at 916.48MHz with slightly different specialized radio settings from the Airwire channels. I call this channel 17. In most but not all cases, these Channel 17 devices are interoperable with Airwire Channel 16 @ 916.36MHz. Also, European versions of these older transmitters and receivers operated on 869.85MHz; I call this Channel 18. Here’s my unofficial Table of channels and frequencies.
The ProMiniAir has some features that may be more interesting than commercial offerings. See the Comparison Tables below.
Name
Airwire Receiver Compatible?
Channels
Power Level Adj
Any DCC Input
TVD DRS1 Transmitter
No
Ch 17 (or 18(E))
No
Yes
Airwire T5000
Yes
0-16
Yes
No
NCE Gwire Cab
Yes
0-7
Yes
No
S-Cab Throttle
No
17
No
No
ProMini Air Transmitter
Yes
0-17, 18(E)
Yes
Yes
Comparison of wireless DCC transmitters
In fairness, the manufacturers of the Airwire T5000, the NCE Gwire Cab, and the S-Cab Throttle hand-held throttles never intended to interface with standard DCC throttles. But, as Tam Valley Depot recognized, it is advantageous to use any device that supplies DCC to the rails and transmit this DCC wirelessly to DCC-compatible receivers.
A notable limitation of the Tam Valley Depot DRS1 transmitter is that it does not provide DCC “IDLE” packets that the Airwire receivers require unless the original DCC throttle does so (most, if not all, do NOT). Also, the Tam Valley Depot DRS1 transmitter can only broadcast on one Channel (near Airwire Channel 16, which I have designated Channel 17 @ 916.48MHz).
Shown in the Table below are the comparisons for wireless DCC receivers.
Name
Channels
DCC Filtering?
Channel Auto Search
TVD DRS1, MK IV
0-17, 18(E)
None
Yes
Airwire CONVRTR
0-16
Always On
Yes (Limited)
QSI Gwire
0-7
None
No
S-Cab LXR receiver
17
None
No
ProMini Air
0-17, 18(E)
None or On
Yes
Comparison of wireless DCC receivers
The most notable difference among the receivers is “DCC filtering,” i.e., how the receiver behaves when losing a valid RF DCC signal.
When the TVD DRS1 or QSI Gwire receivers lose a valid RF signal, they output random pulses to the decoder. I have discussed the pros and cons of this in another post.
On the other hand, the Airwire CONVRTR outputs constant-level DC when it loses a valid RF signal or doesn’t receive enough DCC “IDLE” packets. Again, as discussed in another post, the DCC decoder may halt the locomotive dead in its tracks when it receives this constant-level DC, which may or may not be what the user wants.
The Airwire CONVRTR performs “DCC filtering” by periodically evaluating whether it’s receiving DCC “IDLE” pulses. So, even if a stream of completely-valid DCC packets is received, but there are few or no “IDLE” packets, the Airwire CONVRTR will become inactive and output constant DC to the decoder.
These characteristics of the Airwire receivers are why Tam Valley DRS1 transmitter will usually NOT work with Airwire CONVRTR receivers because the DRS1 will not insert additional DCC “IDLE” packets! The Tam Valley Depot DRS1 transmitter is a passive participant: if the input DCC throttle doesn’t produce frequent DCC “IDLE” pulses, then the Tam Valley Depot DRS1 will not transmit frequent DCC “IDLE” pulses.
Stanton designed the S-Cab LXR-DCC receiver specifically for the S-Cab Throttle’s intermittent DCC transmissions. Like the Airwire CONVRTR receivers, the LXR outputs a constant DC voltage when a valid RF signal is lost.
Via OPS mode (by default at address 9901), you can reconfigure ProMiniAir’s output behavior when a valid RF signal is lost. The first option (CV246 -> 0) selects the output of DCC IDLE messages (which the decoder is “comfortable” with, rather than random pulses that might “confuse” the decoder). The second option (CV246 -> 1) selects the output of constant-level DCC.
This reconfigurability makes the ProMiniAir receiver a versatile wireless DCC receiver. The ProMiniAir receiver’s RF DCC detection technique is more sophisticated than Airwire’s. The ProMiniAir receiver detects how long it’s been since it received ANY valid DCC packet. And, after a preset time interval (which is reconfigurable via OPS mode, changing the CV252 value in 1/4 second multiples), the ProMiniAir receiver will output either the DCC “Idle” messages (DCC filtering “off”) or output constant-level DC (DCC filtering “on”). When DCC filtering is “on,” and there is no valid RF signal, the DC level output is reconfigurable via an “OPS” mode setting of CV248 (-> 1 for positive DC, -> 0 for 0V DC) at the ProMiniAir’s DCC address.
Once a valid RF signal is received again, the ProMiniAir receiver detects this condition. It outputs these valid DCC packets to the “DCC amplifier” that sends “track-level” DCC to the decoder.
Another important feature of wireless DCC receivers is Channel selection and searching.
IF YOU SET SOME JUMPERS, the TVD DRS1 receiver will “listen” on a fixed Airwire Channel. Otherwise, the DRS1 will automatically search the Airwire Channels for a valid RF signal if you do NOT insert the jumpers. This behavior may or may NOT be a good idea if multiple wireless DCC transmitters transmit simultaneously on different Channels. And changing the Channel selection behavior (fixed Channel or auto-scan) requires physical access to the receiver to connect or disconnect jumpers.
On startup, the Airwire CONVRTR “listens” for a valid RF signal on its “startup” channel (which is reconfigurable by accessing a CV using the wireless throttle’s “OPS” mode). If the CONVRTR finds no valid RF signal after a given time, the CONVRTR will switch to Channel 0. This behavior is usually a good idea.
Like the Airwire CONVRTR, on startup, the ProMiniAir receiver will “listen” for valid RF on its “startup” Channel (default, 0) stored in EEPROM memory. This startup channel is changeable using the transmitting throttle’s “OPS” mode by setting CV255 to 0 through 18 at the ProMiniAir transmitter’s DCC Address (default, 9901). Like the TVD DRS1 receiver, if the ProMiniAir does not find a valid RF signal on its startup channel, the ProMiniAir receiver will then auto-scan Channels 0(A), 18(E), 17(S), 1(A), 2(A), …, 16(A) (in that order) for valid RF signal (A=Airwire channels, E=European channel @869.85MHz, S=S-Cab Channel @ 916.48MHz). This scan sequence guarantees that a wireless DCC transmitter (if one is available) is selected, but only if the ProMiniAir does NOT find a valid RF DCC signal on its startup Channel from another wireless DC transmitter.
Once “locked on” to a Channel. The ProMiniAir Receiver will continue to “listen” on this Channel, even if the transmitter is turned off or the signal is lost. This allows the ProMiniAir Receiver to pick up signals on the “locked on” Channel once the transmitter is turned back on or the signal is re-established.
If the ProMiniAir receiver finds no valid RF DCC signal on any Channel on startup, it will select Channel 0 and wait for a valid RF DCC signal. Also, upon reset, the ProMiniAir’s Channel search process will be unchanged: it will try the “startup” channel stored in EEPROM memory, then try auto-searching Channels, and if all else fails, wait on Channel 0.
So, in summary, we are offering the ProMiniAir DCC transmitter and receiver to provide a low-cost alternative with features not entirely found in commercial offerings.
You are provided with a few additional components when buying a ProMiniAir receiver or transmitter. In the case of the ProMiniAir transmitter, we include a simple “DCC Converter” PCB that converts DCC output to the track into Ground, 5V power, and 5V logic DCC. These outputs supply the ProMiniAir transmitter with power and DCC packets to transmit, so no additional power supply is necessary.
For the ProMiniAir receiver, we include a low-cost “DCC amplifier” that converts the ProMiniAir receiver’s 5V logic DCC back to DCC. In its typical configuration, the onboard DCC decoder would pick up from the track (again, discussed in detail below). The ProMiniAir receiver can be powered directly from the battery or a small external 5V power supply.
This modularity keeps costs down, allows for easy replacement of components rather than the entire assembly, and enables the use of commodity components less susceptible to supply-chain disruptions.
ProMiniAir transmitter connectionsStandalone ProMiniAir transmitter connectionsProMiniAir receiver connections for a DRV8871 (3.6) amplifierProMiniAir Receiver connections for a Cytron MD13S (13A) amplifier
And you will need an antenna of your choosing! I love antennas, but your antenna requirements are too diverse to offer a “one size fits all” antenna solution. We provide an FCC/IC-approved Anaren “whip” antenna that connects to the U.FL connector on a 10-pin transceiver daughterboard. This antenna should work well for most transmitter applications and is FCC/IC-approved for “intentional radiators.”
For the ProMiniAir receiver, some can use the small whip antenna without modification; others will need to run an antenna connecting cable to a small, externally-mounted antenna. We discuss several excellent antenna options below.
Documentation
The definitive source of information for the ProMiniAir transmitter and receiver is available here.
Kit Assembly
We no longer offer the ProMiniAir as a kit.
Firmware Installation
The ProMiniAir Tx and Rx are provided with the firmware already loaded. These instructions are only for advanced users who want to update the firmware.
The source code is available from this GitHub site. Locate the source code in a directory where the Arduino IDE can find it. You should retain the subdirectory structure to access the “project” with the Arduino IDE.
How to download the GitHub zip file that will maintain the directory structure
If you want a transmitter or receiver, edit libraries/config/config.h to select the “define” for the transmitter or receiver.
For a receiver (Rx), config.h should look like this:
...
// #define EU_434MHz
/* For World-Wide 2.4GHz ISM band*/
// #define NAEU_2p4GHz
//////////////////////////////
// Set Transmitter or Receiver
//////////////////////////////
/* Uncomment ONLY ONE #define*/
/* For receiver*/
#define RECEIVER
/* For transmitter*/
// #define TRANSMITTER
/////////////////////////////////////////////////
// Set the default channel for NA/EU 900MHz only!
/////////////////////////////////////////////////
#if defined(NAEU_900MHz)
/* Uncomment ONLY ONE #define*/
/* To set the default to NA channel 0 for 869/915MHz ISM bands only!*/
#define NA_DEFAULT
/* To set the default to EU channel 18 for 869/915MHz ISM bands only!*/
// #define EU_DEFAULT
#endif
//////////////////////////////////////////
// Set the transceiver's crystal frequency
//////////////////////////////////////////
/* Uncomment ONLY ONE #define*/
/* For 27MHz transceivers (e.g., Anaren 869/915MHz (CC110L) and Anaren 869MHz (CC1101) radios)*/
// #define TWENTY_SEVEN_MHZ
/* For 26MHz transceiver (almost all other radios, including Anaren 433MHz (CC1101), 915MHz (CC1101), and 2.4GHz (CC2500) radios)*/
#define TWENTY_SIX_MHZ
...
If you want a transmitter (Tx), then config.h should be
...
// #define EU_434MHz
/* For World-Wide 2.4GHz ISM band*/
// #define NAEU_2p4GHz
//////////////////////////////
// Set Transmitter or Receiver
//////////////////////////////
/* Uncomment ONLY ONE #define*/
/* For receiver*/
// #define RECEIVER
/* For transmitter*/
#define TRANSMITTER
/////////////////////////////////////////////////
// Set the default channel for NA/EU 900MHz only!
/////////////////////////////////////////////////
#if defined(NAEU_900MHz)
/* Uncomment ONLY ONE #define*/
/* To set the default to NA channel 0 for 869/915MHz ISM bands only!*/
#define NA_DEFAULT
/* To set the default to EU channel 18 for 869/915MHz ISM bands only!*/
// #define EU_DEFAULT
#endif
//////////////////////////////////////////
// Set the transceiver's crystal frequency
//////////////////////////////////////////
/* Uncomment ONLY ONE #define*/
/* For 27MHz transceivers (e.g., Anaren 869/915MHz (CC110L) and Anaren 869MHz (CC1101) radios)*/
// #define TWENTY_SEVEN_MHZ
/* For 26MHz transceiver (almost all other radios, including Anaren 433MHz (CC1101), 915MHz (CC1101), and 2.4GHz (CC2500) radios)*/
#define TWENTY_SIX_MHZ
...
Two further options are available. The first option selects the crystal frequency of the FCC/EC-approved transceiver: 27MHz (Anaren) or 26MHz (Ebyte). The second option specifies North American or European default use.
After you complete downloading the firmware into the Pro Mini, please do not remove the USB connection from the computer until the “secondary” LED, which indicates attempted communication over the SPI (serial peripheral interface), flashes on (it will not be bright). This step ensures you properly initialize the EEPROM!
You load the firmware into the Pro Mini MCU using an “AVR ISP,” such as the Sparkfun Pocket AVR Programmer or a less-expensive clone. This “ISP” downloading mode will bypass and erase the bootloader to directly load the firmware into the Pro Mini MCU. On boot-up with the bootloader now erased, the Pro Mini MCU will almost instantly supply “5V logic DCC” to the DCC amplifier, which provides the DCC decoder with standard DCC waveforms. There is no “boot-up DC” or need to set CV29, bit2=0. (I set it anyway.) With this solution, all DCC decoders I’ve tried (ESU, Zimo, MTH) startup without the “boot-up jerk.”
This “ISP” form of loading firmware is not as extensively used by folks using the Arduino IDE, but ISP loading is easily accessible within the Arduino IDE. The overly-brief method of ISP programming steps is the following:
Remove the transceiver daughterboard and the jumper (if inserted).
Connect the USBtinyISP (or other) Programmer (with power switch ON to supply 5V DC to the ProMiniAir PCB while programming) to the 6-pin connector on the ProMiniAir.
From the Arduino IDE, Select Tools → Programmer → “USBtinyISP” (or whatever ISP programmer you use).
Select the AirMiniSketchTransmitter sketch.
Select Sketch → Upload using a Programmer.
The Arduino IDE will compile the sketch and download the resulting firmware to the Pro Mini via the USBtinyISP, bypassing (and erasing) the bootloader.
Once the ProMiniAir receiver or transmitter firmware is installed in the Pro Mini and inserted into the ProMiniAir PCB, the ProMiniAir is ready for integration!
Integration
You must establish several connections to complete the ProMiniAir receiver (Rx) integration or transmitter (Tx).
Overview of Connections
See the picture below for an overview of the connections to and from the ProMiniAir. Which connections you use depends on whether the ProMiniAir will act as a receiver (Rx) or a transmitter (Tx). THERE IS NO PROTECTION AGAINST INCORRECT BATTERY OR EXTERNAL POWER CONNECTIONS!!! You will destroy the ProMiniAir immediately if you reverse the GROUND and POSITIVE POWER SUPPLY connection!
Data and power connectionsfor PMA RxData and power connections for PMA Tx
The Anaren and Ebyte transceiver daughterboards have a versatile U.FL plug for antenna connections. You can plug in either the Anaren whip antenna we provide or a U.FL-to-SMA or U.FL-to-RP-SMA cable that screws into a remotely-mounted antenna. Also, a two-pin output provides Ground and the DCC input to (Tx) or output from (Rx) the RF transceiver board, serving as signals to an oscilloscope for waveform review. See the figure below for details on these connections.
ProMiniAir antenna connector (female RP SMA) and transceiver DCC input/output
The ProMiniAir has several connections that provide an AVR programmer, I2C display outputs, and 5V logic DCC inputs or outputs. See the photo below.
ProMiniAir connections for AVR programmer, I2C display output, and 5V logic DCC input or output
We will break down these connections for the ProMiniAir receiver and transmitter in the following two sections.
Receiver Connections
Several options exist for providing power, starting with the ProMiniAir configured as a receiver (Rx). The first option is to use external battery power and jumper the +5V and +5V (Battery) pins to use the onboard 5V regulator to provide board +5V supply.
ProMiniAir power connection options (for Rx only, the Tx receives power from the DCC Converter).
Since you may not like the heat generated by the onboard 5V regulator when you supply power with external battery power and install the jumper, as an alternative, you may use an external +5V power supply, as shown below, where the external power supply provides Ground and +5V. Of course, you do NOT install the jumper.
ProMiniAir receiver powered by an external +5V power supply (older PMA version, but the connections are the same for newer versions)Close-up of ProMiniAir receiver power connections to an external +5V power supply (older PMA version, but the connections are the same for newer versions)
The ProMiniAir receiver must connect to an external DCC amplifier that converts the 5V logic DCC from the ProMiniAir receiver to DCC A/B that a DCC decoder requires. This DCC amplifier uses battery power and the inputs from the ProMiniAir receiver to provide the power and DCC messages, coded as a bipolar DCC waveform, to the decoder for both power and DCC messages. These “DCC amplifiers” are usually medium to large amperage amplifiers that accept pulse width modulation (PWM) input to provide precision output control for electric motors. The maximum PWM frequency of these amplifiers is usually high enough (> 20kHz) to reproduce DCC packets accurately.
Depending on the particulars of your installation, the author will provide an appropriate DCC amplifier as part of your PMA Rx purchase.
Close-up of the inputs to the DCC amplifier from the ProMiniAir receiver
As shown below, some DCC amplifiers have specialized connector configurations for a GROVE-compliant amplifier.
Example of another DCC amplifier’s connections to the ProMiniAir receiver
Integration of the ProMiniAir Receiver into a Locomotive
Of course, the real purpose of the ProMiniAir receiver is to integrate it into a locomotive for wireless DCC control using an onboard battery as power. An excellent high-power (13A continuous) DCC amplifier may be purchased here, as shown below. Unless determined otherwise for size constraints, this Cytron MD13S amplifier is the one we provide with the ProMiniAir receiver. You can successfully use more expensive high-amperage amplifiers (about $30 US as of 2020) found at Pololu here or here. These amplifiers are smaller (0.8″ x 1.3″) than the Cytron.
ProMiniAir receiver integration with battery power, DCC amplifier, and antenna (older PMA version, but the connections are the same for newer versions)Example Installation
Transmitter Connections
Let’s turn the ProMiniAir used as a transmitter (Tx) of DCC messages from any DCC-compatible throttle.
The photo below shows the connections between an interface board that takes throttle DCC A/B inputs (“track” DCC) and rectifies these inputs to provide Ground and +5V power supply output. This “DCC Converter” PCB also “taps off” the DCC A input and converts it to a 5V logic DCC output suitable for the ProMiniAir transmitter. These outputs provide the ProMiniAir transmitter with Ground, +5V power, and 5V logic DCC input.
We provide the “DCC Converter” PCB as part of your PMA Tx purchase.
Photo of ProMiniAir receiver connections to a “DCC Converter” PCB that supplies the ProMiniAir transmitter with Ground, +5V power, and 5V logic DCC. The ProMiniAir transmitter does NOT connect to a battery or use the jumper connecting +5V to +5V (Battery)!Close-up of ProMiniAir transmitter connections to the “DCC Converter” PCB. The jumper connecting +5V to +5V (Battery) is NOT used! (older PMA version, but the connections are the same for newer versions)
The user can change the ProMiniAir transmitter’s Channel (Airwire channels 0-16, S-Cab channel 17, and EU channel 18) and Power Level (0-10) by setting the DCC throttle’s address to that of the ProMiniAir transmitter’s (9900 by default). Then, using the throttle’s OPS mode, change the value of a configuration variable (CV255 for Channel: 0-16, and CV254 for Power Level: 0-10), exit OPS mode, and change the throttle back to the locomotive’s DCC address.
Receiver/Transmitter Antenna Connections
For the ProMiniAir transmitter, we strongly urge you to use the FCC/IC-approved Anaren “whip” antenna supplied with the surface-mounted transceiver to a 10-pin interface daughterboard. This whip antenna/transceiver combination is FCC/IC-approved as an “intentional radiator.” You can purchase antennas for the ProMiniAir transmitter online from many sites for experimentation purposes. For fixed installations of the ProMiniAir transmitter, we suggest reputable products from Linx, such as their SMA one-half wave antennas with an internal counterpoise. You can find these antennas at Digi-Key, e.g., ANT-916-OC-LG-SMA ($10.55) and ANT-916-CW-HWR-SMA ($12.85). The former antenna has a slightly better gain (2.2dBi versus 1.2dBi) but is somewhat longer (6.76″ versus 4.75″).
Linx half-wave antennas. The ANT-916-OC-LG-SMA has a better gain than the ANT-916-CW-HWR-SMA at the expense of being 42% longer.
For the ProMiniAir receiver or the ProMiniAir transmitter, where a small, remotely-mounted antenna is needed, we again recommend Linx antennas such as the ANT-916-CW-RCS or ANT-916-CW-RAH.
The ANT-916-CW-RCS is an excellent choice for a small antenna with a 3.3 dBi gain. It is available from Digi-Key or Mouser and note the male RP SMA connector.The ANT-916-CW-RAH is another excellent choice for a small antenna (2.2 dBi) available from Digi-Key or Mouser. The connector shown here is a male RP SMA, but male SMA connectors are also available from Digi-Key and Mouser.
Diagnostic Outputs
The ProMiniAir receiver or transmitter provides diagnostic outputs that are not required for operation but are helpful for troubleshooting or just for fun:
You can monitor the transceiver’s output (in Rx mode) or input (in Tx mode) on the output DIP pins described above.
“I2C” outputs can drive an inexpensive two rows 16 columns I2C LCD.
The 2-pin connector provides Ground and the RF transceiver’s transmitted or received DCC signals. An oscilloscope can monitor these signals.ProMiniAir receiver/transmitter connections to an I2C LCD (older PMA version, but the connections are the same for newer versions)Close-up of ProMiniAir receiver/transmitter connections to an I2C LCD (older PMA version, but the connections are the same for newer versions)
The ProMiniAir software automatically searches for a valid LCD I2C address on boot-up. Please make sure you connect only ONE display to the ProMiniAir.
You can also change the ProMiniAir’s DCC address using the throttle’s “OPS” mode. For the transmitter, you use the DCC throttle that connects to the ProMiniAir transmitter (by default at DCC address 9900 (previously 9000)). For the ProMiniAir receiver, you use the wireless DCC throttle transmitting to the ProMiniAir receiver (by default at DCC address 9901 (formerly 9001)). The EEPROM permanently stores the changed address, but this new address is not operative until you power cycle the ProMiniAir.
Configuration and Testing
We default-configured the ProMiniAir receiver and transmitter to operate on Airwire Channel 0. This default can be changed by setting the DCC address to 9901(Rx)/9900(Tx) (the default, which can be changed as described in the Users Manual) to access the ProMiniAir transmitter and in OPS or Programming-on-the-Main (POM) mode setting CV255 to the desired Channel. Valid channels are 0-17 for North American operation or Channel 18 (869.85MHz) for European operation.
Should the ProMiniAir receiver fail to detect valid DCC packets on its default channel during startup, it will cycle through all Airwire Channels to find a Channel producing valid DCC packets. If this cycling fails to find a valid Channel, the ProMiniAir receiver will change to Channel 0 and wait for a valid RF DCC signal. This channel change is not permanent, and on a restart, ProMiniAir will revert to its default channel.
Several other configuration options are available through “OPS” mode programming, as described in the ProMiniAir Users Manual.
We strongly urge the user to test the ProMiniAir before the final deployment. At the least, an inexpensive I2C LCD can be purchased here or here (and numerous other locations) to gain insight into the ProMiniAir’s state. This display is particularly beneficial when using the ProMiniAir as a transmitter.
Examples of Testing (Advanced)
This section is only for the advanced or adventurous. In the examples below, the Yellow waveform is the signal from/to the RF transceiver for Rx/Tx, respectively. The blue waveform is one Channel of the resulting DCC (Rx) sent to the decoder, or DCC received from the throttle via wireless transmission (Tx).
Receiver Testing
The photo below shows the ProMiniAir operating as a receiver. Of course, an RF transmitter wirelessly sends DCC packets. This transmitter may be a dedicated wireless DCC throttle, such as the Airwire Tx5000. Or, it may be a transmitter that converts standard “track DCC” to wireless DCC, such as the Tam Valley Depot DRS1 transmitter or the ProMiniAir used as a transmitter (as discussed in the next section)!
On the LCD, “My Ad: #” is the DCC address of the ProMiniAir itself. The “(L)” means “long” address. Displayed on the second line is the Channel number and whether DCC “filtering” is “off” (Filter: 0, as shown) or “on” (Filter: 1).
Example of output from a ProMiniAir receiver. The yellow signal on the oscilloscope is from the T/R DCC output pin on the ProMiniAir receiver (the green PCB on the left with the red RF transceiver PCB mounted on the left end). The blue trace is the DCC signal produced by the DCC amplifier (the PCB on the right with the blue power/DCC out terminal) from inputs from the ProMiniAir.
The photo below shows the oscilloscope waveforms with no valid RF DCC signal. With filtering off (Filter: 0), the DCC sent to the decoder reproduces the random pulses generated by the receiver.
The ProMiniAir receiver’s outputs when receiving no valid RF DCC. The yellow signal is the RF receiver’s DCC, and the blue signal is one of the DCC outputs from the DCC amplifier that provides input to the onboard DCC decoder.
These two photos show the ProMiniAir’s transceiver and DCC amplifier output when valid RF DCC is received and no valid RF DCC is received. DCC filtering is off, so the PMA outputs DCC Idle messages. The Tam Valley Depot and Gwire receivers simply reproduce the random pulses received by the transceiver.
Valid RF DCC received. The decoder DCC mirrors (blue) the receiver’s DCC (yellow).No valid RF DCC. When DCC filtering is off, the PMA injects DCC IDLE messages (Filter: 0).No valid RF DCC. The random pulses produced by the RF receiver are reproduced by the output DCC, and this is what Gwire and Tam Valley Depot receivers produce.
The user can reconfigure the ProMiniAir receiver using the throttle’s “OPS” mode. Setting the wireless throttle DCC address to 9901 now shows that the Msg address (“Msg Ad: #”) matches the ProMiniAir receiver’s address (“My Add: #”).
Set DCC filtering “on” by selecting the ProMiniAir’s address (9901 in this case). Note that the MSG address now matches ProMiniAir’s address.
Change CV246 to “1” in OPS mode, which will turn “on” the ProMiniAir receiver’s DCC filtering.
In “OPS mode,” setting CV246 to “1.” The display will indicate that you changed CV246.
The display now shows that DCC filtering is “on.”
In “OPS mode,” setting CV246 to “1.” The display will indicate that you changed CV246.
Exiting OPS mode and changing the throttle to the locomotive’s address now shows an updated “Msg Ad: #” with DCC filtering “on.”
Then change the address back to the locomotive’s address. The display now shows DCC filtering is “on.”
Below is the transceiver’s and DCC amplifier’s DCC output when transmitting valid RF DCC.
Again, the receiver and decoder DCC when a valid RF DCC signal is received.
If we turn off the wireless transmitter/throttle sending RF DCC, now the transceiver outputs random pulses (yellow). Since filtering is “on,” the ProMiniAir receiver firmware detects “bad” waveforms that do not appear to represent a valid DCC packet. The ProMiniAir receiver then outputs a constant-level signal that causes the DCC amplifier to output a high level on DCC A (blue) and zero Volts on DCC B (not shown). This behavior is similar the that of the Airwire receivers. However, the detection mechanism for Airwire receivers is simply the lack of a sufficient frequency of DCC “IDLE” packets, not an analysis of the transceiver’s pulse train.
The waveforms when no valid RF DCC signal is received. With filtering on (Filter: 1), DCC A sent to the decoder is positive, and DCC B is zero, assuming that you set CV248 to “1”. If you set CV248 to zero, DCC A is zero, and DCC B is positive.
Repeating the process of changing the wireless throttle’s DCC address to 9901, going into “OPS” mode, changing CV246 to “0”, exiting “OPS” mode, and switching back to the locomotive’s DCC address will now set DCC filtering to “off.”
You can repeat selecting the ProMiniAir’s address and, in OPS mode, set CV246=0 to turn the filtering back off and then set the address back to the locomotive’s.Changing the address back to the locomotive’s address indicates that the DCC filtering is off (Filter: 0).
So, when we turn off the wireless DCC throttle/transmitter, the DCC amplifier’s output (blue) again displays the DCC IDLE messages output by the ProMiniAir receiver.
When no valid RF DCC is received, the ProMiniAir receiver injects DCC IDLE messages amplified by the DCC amplifier and sent to the decoder.
Transmitter Testing
We now focus on testing when using the ProMiniAir as a transmitter.
With the same ProMiniAir, the Pro Mini was re-flashed with the transmitter firmware. The “DCC Converter” PCB (the PCB on the right) converts any throttle’s DCC to Ground, +5V power, and 5V logic DCC for input to the ProMiniAir transmitter (the PCB on the left).
The display will alternate between showing the ProMiniAir transmitter’s DCC address (“My Ad: #”) and the transmitted DCC packet’s DCC address (“Msg Ad: #”). The transmitting Channel (“Ch: #”) and Power Level (“PL: #”) display on the second line.
Note the ProMiniAir transmitter’s ID.The LCD alternately displays the throttle’s address and the ProMiniAir’s address and shows the Channel number and Power Level.
Below is an oscilloscope trace of the input DCC from the throttle (blue) and the DCC transmitted by the RF transceiver on the ProMiniAir transmitter. Since the wireless DCC must keep the Airwire RF receiver “happy” with numerous DCC “IDLE” packets, the ProMiniAir transmitter evaluates the incoming DCC from the throttle. When the throttle outputs frequent, redundant DCC packets, the ProMIni Air transmitter occasionally inserts DCC “IDLE” packets instead of one of the redundant packets. So, the input DCC and the transmitted DCC will not precisely match. Since DCC throttles send many redundant DCC packets, the locomotive will receive sufficient DCC packets to operate correctly.
The DCC sent out (yellow) will not precisely match the throttle DCC because of slight timing delays and the occasional insertion of DCC “IDLE” messages that are required to keep Airwire receivers “happy.”A shorter time scale than the previous photo
You can reconfigure the ProMiniAir transmitter by setting the throttle’s DCC address to 9900 (which can be changed) and then going into the “OPS” mode to set configuration variables (CV) to new values.
Setting the throttle’s address to 9900 allows the throttle to reconfigure the ProMiniAir in OPS mode.
Once we have changed the throttle’s DCC address to 9900, note that the message address (“Msg Ad: #”) now matches the ProMiniAir’s address (“My Ad: #”).
The display now indicates that the message address matches ProMiniAir’s address.
For example, changing CV246 to “6” while in OPS mode will reset the ProMiniAir transmitter’s Power Level to 6, as indicated by the below display.
In OPS mode, setting CV254 to 0-10 changes the output power level, as indicated here.
After exiting the “OPS” mode, we see that the display reflects the new Power Level (“PL: #”).
The Power Level is now 6.Note that Msg and My Address are the same.
Changing the throttle’s DCC address back to the locomotive’s address will sometimes show “Msg Ad: 255(S)”, which means that the ProMiniAir transmitter sent out a DCC “IDLE” packet to make the Airwire receiver “happy.”
Changing the throttle’s address back to the locomotive’s allows the ProMiniAir to insert occasional DCC “Idle” messages, indicated by a message address of 255. The IDLE message keeps Airwire receivers “happy.”
A display refresh (every 4 seconds) will most likely display the locomotive’s DCC address, 1654. The “(L)” means “long” address.
The display will alternately show the locomotive address and the ProMiniAir’s address.
Conclusion and Further Information
The ProMiniAir is an inexpensive and hopefully fun introduction to wireless DCC control of your model railroad locomotive!
Please get in touch with the author on this site to purchase the ProMiniAir receiver or transmitter. The ProMiniAir transmitter or receiver (with their additional DCC Converter or DCC amplifier and wiring harness) is only $39.99 + shipping. You can also purchase my offerings on eBay by searching for “ProMiniAir.”
The Stanton Cab (or S-Cab) is a series of dead-rail transmitters and receivers developed and sold by dead-rail pioneer Neil Stanton, Ph.D. S-Cab products are available at this site.
Stanton offers a hand-held transmitter, the S-Cab Throttle, specifically designed to transmit to S-Cab RF receivers. These receivers include the S-CAB Radio Receiver (LXR-DCC) and Loco Receivers for HO, On3, On30, and some S-scale installations. Also, Stanton will provide an S-Cab receiver coupled with decoders for larger scales. The available options are discussed on the S-Cab website here.
The S-Cab Throttle and receivers operate at 916.48MHz or 918.12MHz (single frequency only!). The former frequency is close to Airwire Channel 16 (916.36MHz), and the latter is the same frequency as Airwire Channel 11. However, Airwire hand-held transmitters WILL NOT WORK with S-Cab receivers at either Channel 16 or 11. And Airwire receivers WILL NOT WORK with the S-Cab Throttle.
I successfully determined RF settings that allow the ProMiniAir transmitter (PMA Tx) to operate with the S-Cab receivers (such as the LXR-DCC). So I have added an S-Cab compatible Channel 17, which required moving the European Channel 17 to Channel 18.
The specialized RF settings for Channel 17 also allow the S-Cab Throttle to transmit to the ProMiniAir receiver (PMA Rx) with just a tiny wrinkle to establish communication (more below).
You should note that the ProMiniAir interoperability is with S-Cab products operating at 916.48MHz. Contact the author should you need this interoperability at 918.12MHz.
General Discussion
Stanton designed his products to operate with intermittent transmissions from the S-Cab Throttle to the S-Cab receivers. This practice is at variance with other transmitters such as Airwire hand-held throttles, the Tam Valley Depot DRS1 transmitter, the NCE Gwire Cab, and the ProMiniAir transmitter.
S-Cab Receiver Interoperability with the ProMiniAir Transmitter
I used the S-Cab LXR-DCC receiver for interoperability testing with the PMA Tx. See the photo below.
The S-Cab LXR-DCC receiver
[Warning: Technical, you can skip this paragraph.] Since the LXR-DCC would NOT operate on Airwire Channel 16 (916.36MHz), I devised more specialized RF settings that allow the PMA Tx to transmit successfully to the LXR-DCC receiver. The new “S-Cab Channel 17” transmits at 916.48MHz with a reduced “deviation” frequency FDEV of 25kHz instead of the Airwire channels’ value of 50kHz. Shifting the RF transmission from the “center frequency” FC (916.48MHz in our case) by FDEV indicates a logic transition. Thus a series of pulse transitions are generated by the timing of transmitter frequency shifts: FC -> FC+FDEV -> FC -> FC+FDEV -> … This encoding technique is called Frequency Shift Keying (FSK).
The photo below shows the DCC transmissions from the PMA Tx on Channel 17 and the DCC output from the LXR-DCC. The waveforms clearly show that the PMA Tx successfully transmits to the LXR-DCC.
Demonstration that the ProMiniAir transmitter (yellow waveform) successfully transmits to the LXR-DCC receiver (blue waveform) on Channel 17. Note the very slight time delay of the LXR-DCC’s waveform.
There’s not much more to say about using the ProMiniAir transmitter with S-Cab receivers: set the PMA Tx to channel 17!
As a parenthetical note, Channel 17 will also work with the older Tam Valley Depot (TVD) Mk III receiver/amp and the NCE D13DJR wireless decoder. Both use the now-discontinued Linx ES Series receiver operating at 916.48MHz. Unlike the S-Cab LXR-DCC, they will also work on Airwire Channel 16.
S-Cab Throttle Interoperability with the ProMiniAir Receiver
So now, let’s turn to operating the S-Cab Throttle with the PMA Rx. Since the S-Cab Throttle transmits at 916.48MHz, the PMA Rx must use its automatic “channel search” capability to “find” the intermittent transmissions at 916.48MHz with an FSK deviation frequency of 25kHz.
The S-Cab Throttle’s intermittent transmissions are where the “wrinkle” occurs. The PMA Rx’s channel search after power on quickly searches for transmissions in the following channel sequence: 0(A), 18(E), 17 (S-Cab), 1(A), 2(A), 3(A), …, 16(A), where (A) mean Airwire channel, (E) means European ISM frequency 869.85MHz, and (S-Cab) means for S-Cab at 916.48MHz.
Since the S-Cab Throttle’s transmissions are intermittent, if the operator does nothing, the S-Cab Throttle might not be transmitting in the short time window when the PMA Rx is looking for transmissions on Channel 17. So, to force the S-Cab Throttle into nearly continuous transmissions, slide the speed control up and down continuously for several seconds while the PMA Tx is powering up to guarantee the PMA Tx has transmissions on Channel 17. If the PMA Tx does not “sync up” with the S-Cab Throttle, try again by turning the PMA Tx off and back on while sliding the S-Cab’s speed control up and down.
The video below demonstrates that the PMA successfully receives S-Cab transmission since the DCC address displayed by the PMA Rx matches the S-Cab’s loco address (4) and the PMA Rx auto-selected Channel 17.
Video demonstration of syncing the S-Cab Throttle with the ProMiniAir receiver. Note the following: 1) sliding the speed control back and forth at PMA Tx power-on, 2) the PMA Rx’s finding transmissions on Channel 17, 3) the PMA Rx displays the correct loco address (4) with a valid DCC command, and 5) with no action (and transmissions) from the S-Cab Throttle, the PMA Rx outputs a DCC idle.
Conclusion
I have updated the ProMiniAir transmitter and receiver firmware with a new Channel 17 to allow interoperability with the S-Cab throttle and S-Cab receivers. This new channel will also work with the Tam Valley Depot Mk III receiver and NCE D13DJS wireless decoder, although Airwire Channel 16 will also work with them. To make “room” for this new channel, the European channel (at 869.85MHz) has been moved to Channel 18.
Typical configuration using smartphone/tablet throttle app with dead-rail
Introduction
Numerous excellent posts (here and here) describe how to use a smartphone to control model railroad locomotives, frequently using a “standard” DCC throttle or “station” as an “intermediary” that interlaces DCC commands from multiple sources and applies the resultant DCC power/signals to tracks that are picked up by one or more locomotives’ wheels electrically connected to a DCC decoder.
After reviewing these posts and understanding how this technique works, it’s a nearly effortless step to replace “DCC on the tracks” with wireless DCC transmissions to multiple locomotives. This “dead-rail” (battery-powered, radio-controlled) technique allows multiple locomotives to be simultaneously controlled from multiple throttles, be they smartphone apps or “standard” DCC throttles.
To be more specific, with minimal effort, it’s possible to use smartphone apps, such as WiThrottle, in conjunction with standard DCC throttles to control multiple dead-rail locomotives equipped with RF receivers from CVP (Airwire), Tam Valley Depot (DRS1 MkIII and MkIV), QSI (GWire), and OscaleDeadRail (ProMiniAir). Using other apps is also feasible, but I will confine this post to my personal experience and give you a specific example of how I accomplished this goal.
What’s Required
Of course, you will need to load a smartphone throttle app such as WiThrottle, and other apps are also for Android and iOS. For communication from the smartphone app to a standard DCC throttle, I selected the Digitrax LNWI WiFi Interface that connects via LocoNet to my Digitrax DCS52. Similar solutions are available for NCE DCC throttles using WiFiTrax and numerous other DCC throttle purveyors.
Finally, a ProMiniAir transmitter (abbreviated PMA Tx), interfaced to the DCS52 Track Right/Left output by a DCC Converter, is used as the dead-rail transmitter. This transmitter is compatible with multiple dead-rail receivers such as CVP Airwire, Tam Valley Depot (Mk III and Mk IV), Gwire, and the ProMiniAir.
The ProMiniAir transmitter is not merely a passive component in converting track-DCC to wireless DCC transmissions. It attempts to add a sufficient number of DCC “Idle” messages to the transmissions to keep CVP Airwire receivers “happy.” Otherwise, CVP Airwire receivers will not likely respond correctly to wirelessly-transmitted DCC. This feature makes the ProMiniAir transmitter unique among similar products that convert track-DCC to wireless DCC transmissions.
Putting it Together
The photo below shows the connections. If you think about it, the only aspect that is different from using track-based DCC and dead-rail is that the Track Right/Left output from the DCS52 throttle is connected to the ProMiniAir wireless transmitter (via the DCC converter that provides the ProMiniAir with 5V power and logic-level DCC) rather than to actual tracks – that’s all!
The connections for simultaneous dead-rail control by a smartphone app and a standard DCC throttle
I will now walk you through the steps I used to create the demonstration below.
Connect the ends of the LocoNet cable to the LNWI and the LocoNet port on the back of the DCS52. Plug the power into the LNWI, and connect the smartphone to the network provided by the LNWI. Then select the WiThrottle app, which has excellent instructions for choosing a locomotive’s address and configuration. In our case, we use the app to select DCC address #5000, a Z-5 with a ProMiniAir receiver connected to a Zimo MX696KS DCC decoder.
You connect to the LNWI’s WiFi server on your smartphone with SSID Dtx1-LnServer_XXXX-7, where XXXX is a unique number for each LNWI unit. Upon opening your WitThrottle app, it usually automatically connects to the LNWI; if manual configuration is necessary, you connect to address 192.168.7.1, Port 12090.
Then we use the DCS52 throttle to select our Cab Forward with a ProMiniAir receiver connected to a LokSound 4 L decoder at DCC address #4292. Once you turn on track power (which sends DCC to the ProMiniAir transmitter instead of the tracks), the DCS52 throttle will start interlacing DCC commands for locomotives #5000 and #4292, sent out wirelessly by the ProMiniAir transmitter. See the photos below that demonstrate this interlacing.
The PMA’s LCD shows the wireless transmission of a DCC packet to locomotive #4292 originally from the DCS52 throttleThe PMA’s LCD shows the reception of a DCC packet from the smartphone app for subsequent wireless transmission to locomotive #5000
Demonstration
Once you power on the locomotives, they listen and respond to DCC commands that match their DCC address, as shown in the video below.
Demonstration of the Z-5 (#5000, left) controlled by the WiThrottle app and the Cab Forward (#4292, right) directed by the DCS52
Conclusion
I hope you will agree that allowing one (or more!) smartphones/tablets and “standard” DCC throttles or control units to control multiple locomotives by wireless is not complex at all, and that’s part of the power and appeal of dead-rail.
Numerous wireless RF transmitter/receiver (Tx/Rx) options for locomotive control are available in the US and abroad. My discussion is confined to wireless RF transmitter/receiver options that are DCC compatible, which means that the transmitter sends “logic-level” DCC packets. The receiver converts the “logic-level” DCC packets back to “bipolar” DCC packets, as would be transmitted on tracks, that an onboard DCC decoder can “understand.”
Schematic of representative application
Why am I limiting my discussion? Because DCC is a standard, and if you don’t go with solutions that have standards behind them, then you are likely to suffer “vendor lock,” where a single vendor holds you “hostage” with “their” solution. Perhaps that attitude is a bit overblown, but vendors with proprietary solutions tend to lag in innovation for lack of competition, and what happens if the vendor goes out of business?
I know that the NMRA DCC standards have some problems, including the following issues: pending issues under consideration for years; vendors ignoring some parts of the standards; some vagueness in places; and lack of standards for wireless. The DCC standard is imperfect but far better than no standard. Plus, the DCC decoder market is competitive and feature-rich – you can almost assuredly find a DCC decoder that will satisfy your needs.
As a further limitation of this post, I will mostly confine my discussion on DCC-compatible wireless Tx/Rx options to the 902-928 MHz ISM (Industrial, Scientific, and Medical) band because this is where I have direct experience. There is significant and exciting activity in the DCC-compatible 2.4 GHz ISM band (using Bluetooth technology) as well (see BlueRailDCC), but I have no personal experience with this band. Another advantage of the 902-928 MHz ISM band is some interoperability between transmitters and receivers, although there is currently no firm standard behind this interoperability.
DCC-compatible Tx/Rx options are a vast topic that I cannot fully cover in this blog. These options are well-covered in the following links:
Dead Rail Society: This should always be your first stop when looking at topics related to dead-rail. This site is the epicenter of dead-rail. In particular, this page discusses vendors for dead-rail Tx/Rx.
Facebook Dead Rail page: This social media page is a valuable source for the latest announcements and discussions for dead-rail, including Tx/Rx options.
Receivers
Below is my personal experience with 902-928 MHz ISM DCC-compatible receivers.
General Comments
How each of these DCC-compatible wireless receivers handles the loss of valid RF signal from the transmitter is discussed here.
CVP Airwire
A CVP Airwire CONVRTR-60X wireless DCC-compatible RF receiver is mounted to the tender hull’s side using Velcro. The U.FL antenna cable was later connected. The DCC “A/B” output of the CONVTR-60X connects to the “Track Right/Left” inputs of a wiring harness for a LokSound L V4.0 DCC decoder (not yet inserted) on the opposite side of the tender hull.
The company CVP manufactures and supports its Airwire series of products, including hand-held wireless DCC-compliant throttles (such as the T5000 and T1300) and receivers, such as the CONVRTR series that seamlessly connect to DCC decoders onboard the locomotive. As a general comment, CVP provides excellent, detailed installation and operation documentation, partly because they are dominant in some segments of wireless model railroad control. The CONVRTR receiver has some sophisticated features, such as setting its Airwire RF channel purely in software, described in its User Guide.
However, the CONVRTR interacts with the Airwire wireless throttles in ways that make it difficult to impossible to transmit just “garden variety” DCC wirelessly to the CONVRTR for proper operation. The Airwire throttles transmit numerous DCC “Idle” packets as a “keep-alive” message for the CONVRTR. A red LED on the CONVRTR board indicates received signal quality and flickers least when receiving many DCC Idle packets, and the brightness of the LED indicates the received RF power. Typical DCC throttles are not designed with these “keep-alive” concerns in mind and do not output DCC Idle packets often enough to keep the CONVRTR “happy.”
Other than the CVP Airwire transmitters (the T5000 and T1300), the only currently available (the no longer manufactured NCE GWire Cab was also Airwire-compatible) RF transmitter that I am aware of that is capable of communicating with the Airwire CONVRTR is the ProMiniAir, whose open-source software (at GitHub AirMiniTransmitter) intercepts “garden variety” DCC from the throttle and interleaves a sufficient number of DCC Idle packets to communicate correctly with the CONVRTR. This “keep-alive” requirement for the Airwire CONVRTR is challenging to produce, so sometimes a reset of the DCC throttle or the ProMiniAir is required to initially send enough DCC Idle packets to initiate communication with the CONVRTR.
Like the Gwire receiver below, the Airwire CONVRTR “X” versions have a U.FL connector for connecting a shielded antenna cable from the receiver to an externally-mounted antenna. An internal antenna option is also available for CONVRTR mountings that are not surrounded by metal.
QSI Solutions Gwire
Gwire U.FL connector. If using the U.FL connector, detach the wire antenna.
The Gwire receiver operates on Airwire RF channels 0-7 that the user must select from a dial on the device itself. A nice feature of this receiver is an onboard U.FL connector (see the Figure above) that allows the user to connect a shielded antenna cable from the receiver to an externally-mounted antenna – useful when the antenna needs to be on the exterior of a metal locomotive or tender shell. See Blueridge Engineering’s website for details on how to interface the Gwire to any onboard DCC decoder. The Gwire presents no difficulties for wireless 902-914 MHz ISM band DCC-compatible transmitters, and you can find it on eBay at relatively low ($20 US or less) prices.
Tam Valley Depot DRS1, MkIII
Tam Valley Depot DRS1, MKIII in an open-cavity install. Note the built-in long-wire antenna.
The Tam Valley Depot DRS1, MkIII receiver operates only on Airwire RF channel 16 (actually 916.49 MHz, which is close enough to Airwire channel 16 at 916.37 MHz) and makes a suitable wireless DCC receiver. This receiver has a long, single-wire antenna that provides efficient RF reception (see the Figure above). However, placing this wire outside any metal shell would be best, which may be inconvenient in some mounting applications. The DRS1, MkIII, presents no difficulties for the 902-914 MHz ISM DCC-compatible transmitters as long as they transmit near 916.49 MHz. The DRS1, MkIV described in the next section supersedes this receiver.
Tam Valley Depot DRS1, MkIV
The recently-released Tam Valley Depot DRS1, MkIV receiver. Note the internal antenna on the right side of the board.
The Tam Valley Depot DRS1, MkIV receiver is a significant upgrade from the DRS1, MkIII, and operates at the original Tam Valley 916.49 MHz frequency, Airwire Channels 0-16, and at 869.85 MHz (for European operation). The DRS1, MkIV presents no difficulties for the 902-928 MHz ISM DCC-compatible transmitters. It is an interesting choice because it changes channels automatically until it finds a sufficient RF signal carrying DCC packets. See the Figure above for the version that employs an internal antenna that is useful when the receiver is not mounted inside a metal shell.
The DRS1, MkIV with a U.FL antenna connector (and a heatsink update) is now available (see picture below), making it very useful for connecting external antennas outside metal shells. This version of the DRS1 makes it highly competitive in capability and quality with the Airwire CONVTR. Perhaps a future version will provide DC output to the onboard DCC decoder when no valid RF signals carrying DCC packets are available, making it possible to program the DCC decoder’s behavior when no DCC signal is available.
Tam Valley Depot DRS1, MkIV receiver with U.FL connector.
OScaleDeadRail ProMiniAir Receiver
ProMiniAir receiver/transmitter
The inexpensive ProMiniAir receiver presents no issues when used with 902-928 MHz ISM DCC-compatible transmitters. It operates on Airwire RF channels 0–16. It requires a separate, low-cost amplifier (e.g., the Cytron MD13S) to convert the ProMiniAir’s unipolar 5V DCC to bipolar DCC that provides sufficient power to the decoder.
The ProMiniAir’s open-source software is available for download at the GitHub site AirMiniTransmitter.
Transmitters
So far as I’m aware, there are four 902-928 MHz ISM DCC-compatible transmitters: the CVP Airwire T5000 and T1300, the Tam Valley Depot DRS1 transmitter, and the OScaleDeadRail ProMiniAir transmitter.
CVP Airwire Transmitters
The CVP Airwire T5000 and T1300 transmitters are excellent choices for operating with 902-928 MHz ISM DCC-compatible receivers, which will properly communicate with these two transmitters. When I am testing wireless receivers, the T5000 is my “go-to” because, in addition to serving as a DCC-compatible throttle, it can program onboard DCC decoders, via the wireless receiver, in either “OPS” (or Programing-on-the-Main, PoM) or “Service” mode. While the T1300 cannot program the onboard DCC decoders, it serves as a typical DCC throttle.
Of course, the Airwire transmitters send sufficient DCC “Idle” packets to keep the Airwire CONVRTR receivers “happy.”
Tam Valley Depot DRS1 Transmitter
The Tam Valley Depot DRS1 transmitter uses DCC packets produced by any DCC throttle or command station that outputs “bipolar” DCC to tracks. The DRS1 transmitter converts the “bipolar” DCC to “logic-level” DCC and transmits it at only 916.49 MHz, which is close enough to Airwire Channel 16 at 916.36 MHz to be received. This frequency limitation means that only the Tam Valley Depot DRS1, MkIII, and MKIV, and the OScaleDeadRail ProMiniAir receivers can operate with this transmitter if they are receiving on 916.48 MHz or Airwire Channel 16.
While the Airwire CONVRTR can operate on Airwire Channel 16, the DRS1 transmitter is not designed to transmit sufficient “Idle” DCC packets to keep the CONVRTR “happy” since it passively sends along only the DCC packets it receives from the DCC throttle or command station.
OScaleDeadRail ProMiniAir Transmitter
The ProMiniAir transmitter with optional LCD. The antenna in the picture was replaced with a high-quality 1/2-wave Linx ANT-916-OC-LG-SMA antenna from either Mouser or Digi-Key for improved transmission.
OScaleDeadRail provides the ProMiniAir transmitter/receiver that uses open-source software at the Github AirMiniTransmitter site. Like the DRS1 transmitter, it is designed to take inputs from any DCC throttle or command station’s “bipolar” DCC output to tracks (via a simple, low-cost optocoupler provided by OScaleDeadRail) and transmit the “logic-level” DCC on Airwire channels 0-16.
The ProMiniAir transmitter inserts a sufficient number of DCC “Idle” packets into the original throttle-produced DCC to keep the Airwire CONVRTR “happy.” This keep-alive capability, coupled with the transmission on Airwire channels 0-16, ensures that the ProMiniAir transmitter can communicate with any of the 902-928 MHz ISM DCC-compatible receivers discussed in this blog.
This transmitter’s settings, like channel number and output power, can be controlled by the DCC throttle or command station in the “OPS” mode by setting the throttle address to that of the ProMiniAir, which is 9000 by default. An optional LDC display can be attached to the ProMiniAir transmitter for status display. More configuration information is available at the GitHub AirMiniTransmitter site.
Note: This post deals with details of various brands of DCC-compatible, wireless RF receivers operating in the 902-928 MHz “ISM” band that connect to onboard DCC decoders. Some aspects of the discussion may apply to other RF bands as well.
Typical application. In some cases, such as the Airwire transmitters, the throttle and transmitter are combined. Also, the receiver and amplifier may combined, such as for Airwire and Tam Valley Depot receivers.
The designers of various DCC-compatible RF receivers have a couple of strategies for what output to provide to the onboard DCC decoders when a valid RF signal is lost:
Output the random pulses that the RF receiver naturally outputs when a valid RF signal is lost. This option will cause most DCC decoders to maintain direction and speed while the DCC decoder “sifts” the random pulses searching for valid DCC packets.
Output a fixed, positive Direct Current (DC) voltage to one of the DCC decoder’s “Track” inputs and a zero voltage DC the other “Track” input when either a) RF signal is lost, or b) when the RF transmitter does not send sufficiently-frequent “keep-alive” DCC packets. The latter is true for the Airwire CONVRTR. How the DCC decoder responds to these DC “Track” inputs depends upon DCC decoder configuration and, unfortunately, DCC decoder manufacturer discretion.
There are several NMRA-specified Configuration Variables (CV’s) that affect how DCC decoders handle the loss of valid DCC packets and are important to understand when the DCC decoder is connected to the DCC output of DCC-compatible RF transmitters because the RF receivers may lose or receive corrupted RF signal from the dead-rail RF transmitter.
The NMRA standard S-9.2.4, section C “Occurrence of Error Conditions” states “Multi Function Digital Decoder shall have a Packet Update time-out value.” Further down on line 60 the standard states “A value of 0 disables the time-out (i.e., the user has chosen not to have a time-out)”. This part of the NMRA standard is not universally-implemented by manufacturers, and it affects how decoders will respond to the loss of RF transmission of DCC packets. To implement this requirement, the NMRA standard S-9.2.2 has defined the recommended (R), but notmandatory (M), CV11, Packet Time-Out Value. A value of CV11=0 is defined to turn off the time-out, but CV11 is frequently not implemented.
However, another CV that is often implemented addresses some aspects of loss of DCC. The optional (O) CV27, Decoder Automatic Stopping Configuration, is under re-evaluation by NMRA, but the NMRA has taken no definite action some time. Here is what the NMRA standard S-9.2.2 currently (as of 2019) states about CV27:
Configuration Variable 27 Decoder Automatic Stopping Configuration Used to configure which actions will cause the decoder to automatically stop.
Bit 0 = Enable/Disable Auto Stop in the presence of an asymmetrical DCC signal which is more positive on the right rail. “0” = Disabled “1” = Enabled
Bit 1 = Enable/Disable Auto Stop in the presence of an asymmetrical DCC signal which is more positive on the left rail. “0” = Disabled “1” = Enabled
Bit 2 = Enable/Disable Auto Stop in the presence of an Signal Controlled Influence cutout signal. “0” = Disabled “1” = Enabled
Bit 3 = Reserved for Future Use.
Bit 4 = Enable/Disable Auto Stop in the presence of reverse polarity DC. “0” = Disabled “1” = Enabled
Bit 5 = Enable/Disable Auto Stop in the presence forward polarity DC. “0” = Disabled “1” = Enabled
Bits 6-7 = Reserved for future use.
Since DCC decoder manufacturers frequently do implement CV27, what electrical output the DCC-compatible RF receiver provides to the DCC decoder upon loss of a valid RF signal will influence how the DCC decoder responds. We will break this down for various brands of DCC-compatible RF receivers in the 902-928 MHz ISM band in the following subsections.
Note that some DCC decoders will not honor CV27=0; i.e., all auto-stopping features disabled. For example, with CV27 set to 0, the Zimo MX-696, and probably other Zimo DCC decoders as well, will continue speed and forward direction if positive DC level is input to the “Right Track” DCC input, and a zero DC level is input to the “Left Track” DCC input. Under these “track voltage” conditions, the locomotive will stop if originally moving backward. Some (but not all)DCC-compatible RF receivers, such as the Airwire CONVRTR, provide these DC inputs, if a valid RF signal is lost, but only if connected correctly.
The “correct” connection relates to how the user connects the DCC output from the RF receiver to the “Track Right” and “Track Left” inputs of the DCC decoder. Under normal circumstances, when there is a valid RF signal, which way the DCC decoder connects to the RF receiver does not matter. Under the exceptional case of DC-only output by the RF receiver, if it loses a valid RF signal, which way the DCC decoder connects to the RF transmitter does matter. The user will likely want the locomotive to continue forward with the loss of a valid RF signal, so some experimentation is required to determine which of the RF transmitter DCC outputs should connect to which of the DCC decoder’s “Track” inputs to achieve the desired behavior.
Example DCC waveform output from a DCC-compatible RF receiver when there is a valid RF signalExample random pulse output from a DCC-compatible RF receiver when there is no valid RF signal. Note the waveform’s superficial similarity to valid DCC output.
As a further complication, the user should probably turn off the decoder’s “analog” mode of operation by setting Bit 2 of CV29 to 0 to force the decoder to use “NMRA Digital Only” control of ”Power Source Conversion” (see the NMRA standard here). If Bit 2 of CV29 is set to 1, and again we emphasize the user should probably not activate this feature, then “Power Source Conversion Enabled” and then CV12 determines the power source; the most common of which is CV12=1, “Analog Power Conversion.”
Airwire CONVRTR Series
CVP Airwire CONVRTR-60X tender installation. The CONVRTR operates on Airwire channels 0-16. Note that the U.FL antenna lead was later connected to the CONVRTR. The LokSound L V4.0 DCC decoder mounting harness can be seen mounted on the tender wall opposite the CONVRTR, and its Track Left/Right inputs are connected to the CONVRTR-60X’s DCC A/B outputs.
When the CVPAirwire CONVRTR loses a valid RF signal or receives insufficiently-frequent DCC Idle packets, it detects these conditions and outputs a fixed DC voltage to the decoder. Consequently, the user should set CV27 according to the description above.
While it may seem that the user would want the locomotive to stop if its RF receiver loses a valid RF signal, consider what might happen in tunnels or locations remote to the DCC RF transmitter. Getting stuck under these circumstances if a valid RF signal is lost is probably not what the user wants, so we strongly suggest that the user set CV27=0.
The user is cautioned, however, that some DCC decoders, such as the new ESU LokSound 5 L DCC, do not honor the CV27=0 setting unless the “polarity” of the “Track Right/Left” is connected “correctly” to the CONVRTR’s “A/B” output. Experimentation may be required to determine the correct connection, but my experience is: CONVRTR A <–> Decoder Track Right & CONVRTR B <–> Decoder Track Left
QSI Solutions Gwire and Tam Valley Depot DRS1 Series
The QSI Solutions GWire operates on Airwire Channels 0-7. If the U.FL plug (at the upper-left corner of the Linx Transceiver chip) connects to an externally-mounted antenna, the antenna wire at the upper-left corner of the GWire board should be cut off at board level, or better yet, unsoldered.The Tam Valley Depot DRS1, MKIII, operates on Airwire Channel 16The Tam Valley Depot DRS1, MkIV, operates on Airwire Channels 0-16 (as well as other frequencies). Note the internal antenna on the right-hand side of the board.
The QSI SolutionsGwire and Tam Valley DepotDRS1, MkIII and MkIV DCC-compatible RF receivers will output random pulses to the onboard DCC decoder when a valid RF signal is lost, so setting CV27 is probably of no use. On the “plus” side, most DCC decoders will maintain locomotive direction and speed in the presence of these random pulses since the DCC decoder is actively sorting through these pulses for valid DCC packets, which is usually the behavior the user wants.
A Blueridge Engineering webpage describes how to easily modify the GWire for use as an RF receiver for any onboard DCC decoder.
OScaleDeadRail ProMiniAir Receiver
OScaleDeadRail ProMiniAir receiver operates on Airwire channels 0-16. The ProMiniAir can also be configured to operate as a DCC-compatible transmitter that wirelessly transmits DCC from any DCC source on Airwire channels 0-16.
The OScaleDeadRail ProMiniAir receiver has a default long address of 9001. Like the ProMiniAir transmitter, the ProMiniAir receiver’s channel can be reset in “OPS Mode” by setting CV255 to a value in the range of 0–16. The ProMiniAir receiver has the following options when a valid RF signal is lost:
Output random pulses to the onboard DCC decoder: The user can set the ProMiniAir receiver to output the random pulses when it loses a valid RF signal by setting CV246 to 0 in “OPS mode” at the ProMiniAir’s address. In this case, setting CV27 for the onboard DCC decoder is irrelevant because the random pulses from the ProMiniAir receiver will cause the onboard DCC decoder to maintain the speed and direction of the locomotive while it is “sifting” through the random pulses for valid DCC packets.
Output either fixed positive or negative voltage DC to the onboard DCC decoder: In this case, setting CV27 for the onboard DCC decoder at its address is relevant. The user can set the ProMiniAir receiver to output fixed DC voltage when it loses a valid RF signal by setting CV246 to 1 in “OPS mode” at the ProMiniAir’s address. A positive DC voltage is output by setting the ProMiniAir receiver’s CV248 to 1 in “OPS mode” at the ProMiniAir’s address, or a negative DC voltage is output by setting CV248 to 0. If the user does not want the locomotive to stop with the loss of a valid RF signal, then set CV27=0 for the onboard DCC decoder at its address. Of course, setting CV27 to other values (see above) in the DCC decoder will determine how the DCC decoder responds to the fixed DC voltage that the ProMiniAir outputs to the onboard DCC decoder upon loss of a valid RF signal.
Wrap-Up
It’s an unfortunate fact of life that we can lose a valid RF signal from our DCC-compatible transmitter. However, with a little study of DCC decoder documentation, and possibly a bit of experimentation, gracefully coping is definitely possible.
Select the serial port you think is correct, and if it is, the log window at the bottom will cheer your success. If not, try another USB port from the pull-down list.
You should also see the PMA Tx’s LCD show a changed value, now with a new channel!
