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 cost for the PMA Transmitter/WiFi-equipped EX-CommandStation for smartphone dead-rail control is $49.99 on eBay. Search on eBay using “ProMiniAir”, and you will see this and other ProMiniAir offerings.
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. 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 +5V 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, instead of paying for a WiFi device that connects to a commercial DCC throttle at a cost 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 power into the PMA Tx/WiFi-equipped EX-CommandStation, which turns on the ESP8266 WiFi transceiver to broadcast information for your smartphone to pick up, boots up the EX-CommandStation itself, and powers up the ProMiniAir receiver and LCD. You can connect a 9V power to the ProMiniAir transmitter/WiFi-equipped EX-Command station for “take it anywhere” capability. The battery adapter can be found here. A 1200 mAh battery, such as the Energizer Lithium, will last about 4 hours. Rechargeable Lithium-ion 600mAh batteries will last about two hours, but a four-pack with a charger will only set you back about $24.
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 prototype 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 12 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)
OK, these smartphone throttle apps are great, but they have a limitation: they can’t currently send commands in PoM (OPS) 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!
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.
So, there you have it, a wireless way to control a WiFi-equipped EX-CommandStation in Programming on the Main (PoM) mode, also known as OPS 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 power to the EX-CommandStation. 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 power to the EX-CommandStation. This powers up the EX-CommandStation and the ProMiniAir transmitter with its LCD.
Connect the USB cable to the EX-CommandStation and your computer/laptop.
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.
Appendix: Implementation (How I Did It for Do-It-Yourselfers)
The EX-CommandStation consists of several components (with emphasis on our application):
An Arduino microprocessor (for us, the Arduino Mega or clone): the “brain” that takes throttle inputs and converts them to +5V DCC signals, usually for a motor shield.
A motor shield or motor driver: converts the microprocessor’s +5V DCC signals (and other controls) to higher-voltage DCC Track Right/Track Left to power and control locomotives equipped with DCC decoders. Because the track may short-circuit or require too much power, the motor shield or motor driver may provide signals, such as current sense, back to the microprocessor that generates commands to protect the motor shield or motor driver from damage.
Optionally:
WiFi (integrated on the microprocessor PCB, an Arduino shield, or discrete receiver jumpered to the microprocessor PCB): receives wiThrottle-protocol commands from smartphones or tablets via WiFi and sends these commands to the microprocessor.
Ethernet
Bluetooth
Direct connection to a PC
Free, open-source EX-CommandStation software
We need a WiFi-equipped Arduino MEGA and the EX-CommandStation software for our dead-rail application using a smartphone, but what about that motor shield?
A “motor shield” that amplifies the EX-CommandStation’s +5V digital DCC output for controlling and powering locomotives via the tracks is unnecessary since the ProMiniAir transmitter only requires +5V DCC input (along with +5V power, which is available from the EX-CommandStation as well). An added advantage is the “DCC Converter,” which is necessary to convert track DCC from a “traditional” DCC throttle to +5V power, and +5V DCC the PMA transmitter requires is unnecessary. (If you like, we will include the DCC Converter because you may want to use your ProMiniAir transmitter with a “traditional” DCC throttle later.) The modular design of the ProMiniAir transmitters and receivers makes this solution easy and reduces cost.
Based on the information provided by DCC+EX, I selected a Songhe Mega2560 + WiFi R3 because the motherboard has integrated WiFi. The DCC-EX website superbly provides the detailed step-by-step set-up of an EX-CommandStation with integrated WiFi. You also need a 7-9V 1 A power supply, and a battery option is undoubtedly feasible but more expensive.
Since I needed to modify the source code to accommodate the ProMiniAir transmitter integration with the EX-CommandStation, I used this download link. I followed the DCC-EX project installation instructions for the Arduino IDE and only modified the config.h file of the EX-CommandStation software for integration with the ProMiniAir transmitter:
// (more before...)
/////////////////////////////////////////////////////////////////////////////////////
// NOTE: Before connecting these boards and selecting one in this software
// check the quick install guides!!! Some of these boards require a voltage
// generating resistor on the current sense pin of the device. Failure to select
// the correct resistor could damage the sense pin on your Arduino or destroy
// the device.
//
// DEFINE MOTOR_SHIELD_TYPE BELOW ACCORDING TO THE FOLLOWING TABLE:
//
// STANDARD_MOTOR_SHIELD : Arduino Motor shield Rev3 based on the L298 with 18V 2A per channel
// POLOLU_MOTOR_SHIELD : Pololu MC33926 Motor Driver (not recommended for prog track)
// FUNDUMOTO_SHIELD : Fundumoto Shield, no current sensing (not recommended, no short protection)
// FIREBOX_MK1 : The Firebox MK1
// FIREBOX_MK1S : The Firebox MK1S
// IBT_2_WITH_ARDUINO : Arduino Motor Shield for PROG and IBT-2 for MAIN
// |
// +-----------------------v
//
// #define MOTOR_SHIELD_TYPE STANDARD_MOTOR_SHIELD
// This motor shield is for the PMA Tx
#define PMA_TX F("PMA_Tx"), \
new MotorDriver(6, 7, UNUSED_PIN, UNUSED_PIN, UNUSED_PIN, 1.0, 1100, UNUSED_PIN), \
new MotorDriver(5, 4, UNUSED_PIN, UNUSED_PIN, UNUSED_PIN, 1.0, 1100, UNUSED_PIN)
#define MOTOR_SHIELD_TYPE PMA_TX
// (more after...)
The critical part for us is the “7” in the “new MotorDriver” line, which states that the “+” DCC output (+5V logic output between 0 and +5V) is on Pin 7. That’s all we need (along with power) to “feed” the ProMiniAir transmitter! I then recompiled the EX-CommandStation software according to the DCC+EX instructions with absolutely no problem.
The connections to the WiFi-equipped EX-CommandStation to the ProMiniAir transmitter are straightforward: connect GND and +5V to the power connections on the EX-CommandStation motherboard, and the +5V DCC input to Pin 12 (previously Pin 7) on the motherboard.
The connections between the WiFI-equipped EX-CommandStation and the ProMiniAir transmitter
You could purchase the components and set up the WiFI-equipped EX-CommandStation yourself. However, since we can do the set-up legwork for you, you can order the WiFi-equipped EX-CommandStation option for the ProMiniAir for $49.99 on eBay ($5 is donated to DCC+EX). We include the AC to DC power converter (wall 120V AC to 9V DC) for the EX-CommandStation.
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.
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!
