A Low-Cost WiFi-Equipped DCC Base Station for the ProMini Air Transmitter

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 🙁

In a previous post, I showed how easy it was to use a smartphone equipped with a “wiThrottle-compliant” app in conjunction with the ProMini Air transmitter to control your dead-rail locomotive(s) fitted with a variety of receivers such as ProMini Air, Tam Valley Depot DRS1, CVP Airwire, Stanton Cab, QSI Gwire, and NCE. The downside was that you must invest in a WiFi device made for the DCC base station connected to the ProMini Air transmitter. Many folks pushed back on the additional cost and infrastructure to use their smartphone app for dead-rail control using the ProMini Air transmitter.

I searched for a way to provide a low-cost way to use your smartphone in conjunction with the ProMini Air 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 ProMini Air, 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 $70.

The wiThrottle-protocol smartphone apps that will work with this solution include (this list is from DCC-EX):

The important point is that the ProMini Air transmitter, coupled with the WiFi-equipped EX-CommandStation, is a completely self-contained solution for $70. 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
  • Control of accessory/function decoders
  • Programming Track
  • Programming on Main Track

It includes advanced features such as:

  • wiThrottle Server implementation,
  • General purpose inputs and outputs (I/O) for extensibility, and
  • JMRI integration

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 ProMini Air transmitter for dead-rail control. It’s that simple; the technique was easy to implement and is low-cost (about $25, instead of paying for a WiFi device that connects to a commercial DCC throttle, a total of over $200).

Instructions for Using the ProMini Air Transmitter/WiFi-Equipped EX-CommandStation with a Smartphone

What you need:

  1. A smartphone loaded with the wiThrottle-compliant app. See the list above.
  2. A properly configured ProMini Air Transmitter/WiFi-equipped EX-CommandStation. We provide this.
  3. A locomotive(s) equipped with receivers compatible with the ProMini Air transmitter, such as:
    • ProMini Air 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:

  1. Plug 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 ProMini Air receiver and LCD. You can connect a 9V power to the ProMini Air 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.
  2. Go to the smartphone’s WiFi settings:
    1. 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.
    2. 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).
    3. 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.
    4. 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.
    5. 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.
  3. Once connected, go to your throttle app:
    1. When asked for WiFI router configuration, set the IP address to “192.168.4.1” and the port to “2560“.
    2. Once your throttle app connects to the EX-CommandStation, you can select your loco(s), etc.
  4. Turn on your dead-rail locomotives, and control them with your smartphone app!
  5. 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 ProMini Air 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 ProMini Air 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 ProMini Air 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 ProMini Air transmitter sends to onboard locomotive receivers.
Video 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 ProMini Air 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 some CV changes to your dead-rail locomotive’s DCC decoder using PoM (OPS) mode, too!

You may NEVER change the ProMini Air’s configuration, but then again, 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 ProMini Air transmitter (or receiver, for that matter!) or your dead-rail locomotive’s DCC decoder in PoM mode.

Since I own an iPhone, I’ll show you what to do using TCP/IP to Serial Terminal.

What you need:

Steps:

  1. Select the app and enter the IP address and port number, and then connect:
  2. Test using the status command, entering <s> (case sensitive):
  3. See the response:
  4. Enter the command to change the value of CV 255 at address 9900 to a value of 5 by entering <w 9900 255 5> (case sensitive):
  5. Verify that the ProMini Air transmitter, which is at DCC address 9900, the channel has changed to 5:

The steps for using the Android app Serial WiFi Terminal should be similar.

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 ProMini Air 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:

  1. Connect power to the EX-CommandStation. This powers up the WiFi-equipped EX-CommandStation and the ProMini Air transmitter with its LCD.
  2. 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.
  3. On your computer, start up a “terminal” session. A terminal session allows you to type in commands.
  4. 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, which is the default EX-CommandStation address and port.
  5. Your command line will now be waiting for you to enter the text that will be 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.
  6. OK! Now let’s change the ProMini Air 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 ProMini Air transmitter’s LCD, you will see the following:
  7. 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:

  1. Connect power to the EX-CommandStation. This powers up the EX-CommandStation and the ProMini Air transmitter with its LCD.
  2. Connect the USB cable to the EX-CommandStation and your computer/laptop.
  3. 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 ProMini Air transmitter.
  4. Select the “Connect DCC++ EX” button to activate the USB serial connection to the EX-CommandStation.
  5. 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.
  6. Now look at the Debug Console and ensure Debug in “ON.”
  7. 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.
  8. 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!
  9. Disconnect the USB cable.
  10. Use your smartphone to connect the ProMini Air Tx/WiFi-equipped EX-CommandStation as described above.
  11. 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 ProMini Air 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 ProMini Air transmitter!

Final Thoughts

While I called this approach for using a smartphone app with the ProMini Air transmitter a “compromise solution,” if you think about it, with a more centrally-located ProMini Air 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

So, 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 ProMini Air 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 ProMini Air transmitter with a “traditional” DCC throttle later.) The modular design of the ProMini Air 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 ProMini Air 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 ProMini Air 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 resitor 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 ProMini Air 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 ProMini Air transmitter are straightforward: connect GND and +5V to the power connections on the EX-CommandStation motherboard, and the +5V DCC input to Pin 7 on the motherboard.

The connections between the WiFI-equipped EX-CommandStation and the ProMini Air 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 ProMini Air for $40 ($5 is donated to DCC+EX). We include the AC to DC power converter (wall 120V AC to 9V DC) for the EX-CommandStation.

Information Update on the ProMini Air Receiver and Transmitter

Introduction

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 ProMini Air 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 “ProMini Air” 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 ProMini Air. Also, previous versions of the ProMini Air 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 ProMini Air Transmitter and Reciever

Please see this post on an important update on the ProMini Air 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 ProMini Air transmitter. Just plug in power and use your smartphone app to connect to the WiFI-equipped EX-CommandStation and then control your dead-rail locomotive

Both the ProMini Air transmitter and receiver have been significantly reduced in size: 1.1″ x 0.8″, making it possible to mount the ProMini Air receiver and a tiny DCC amplifier in tighter spaces and some HO locomotives.

The new ProMini Air receiver and small amplifier (3.6A)

Feature Comparisons

My goal for offering the ProMini Air 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 ProMini Air 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, and I call this Channel 18. Here’s my unofficial Table of channels and frequencies.

ChannelFrequency (MHz)Comments
0921.37
919.87 
2915.37 
3912.37 
4909.37 
5907.87 
6906.37 
7903.37 
8926.12
9924.62
10 (A)923.12
11 (B)918.12 S-Cab alternative frequency
12 (C)916.87
13 (D)913.62
14 (E)910.87
15 (F)904.87
16 (na)916.37 TVD interoperability w/ Ch. 17
17916.48S-Cab and older Tx/Rx
18869.85European operation
Unofficial channel designations

The “ProMini Air” receiver is compatible with the Tam Valley DRS1 transmitter (Channel 16 or 17), both the CVP AirWire T5000 and T1300 wireless throttles (Channels 0-16), the no longer manufactured NCE GWire CAB (Channels 0-7), and the Stanton Cab Throttle (Channel 17).

The ProMini Air transmitter is compatible with the Tam Valley Depot DRS1 receiver (Channels 0-17, Channel 18(E)), the CVP Airwire CONVRTR receivers (Channels 0-16), the QSI Gwire Receiver (Channels 0-7), the Stanton Cab LXR-DCC receiver (Channel 17), and the NCE D13DRJ wireless decoder (Channel 16 or 17). Of course, the ProMini Air transmitters and receivers are compatible!

The ProMini Air has some features that may be of interest compared to commercial offerings. See the Comparison Tables below.

NameAirwire Receiver
Compatible?
ChannelsPower
Level Adj
Any DCC
Input
TVD DRS1
Transmitter
NoCh 17
(or 18(E))
NoYes
Airwire
T5000
Yes0-16YesNo
NCE Gwire CabYes0-7YesNo
S-Cab ThrottleNo17NoNo
ProMini
Air Transmitter
Yes0-17, 18(E)YesYes
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 to 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.

NameChannelsDCC
Filtering?
Channel Auto
Search
TVD DRS1,
MK IV
0-17, 18(E)NoneYes
Airwire
CONVRTR
0-16Always
On
Yes (Limited)
QSI
Gwire
0-7NoneNo
S-Cab LXR
receiver
17NoneNo
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 are 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 ProMini Air’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 ProMini Air receiver a versatile wireless DCC receiver. The ProMini Air receiver’s RF DCC detection technique is more sophisticated than Airwire’s. The ProMini Air 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 ProMini Air 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 ProMini Air’s DCC address.

Once a valid RF signal is received again, the ProMini Air 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.

The TVD DRS1 receiver will “listen” on a fixed Airwire Channel if you set some jumpers. 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 ProMini Air 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 ProMini Air transmitter’s DCC Address (default, 9901). Like the TVD DRS1 receiver, if the ProMini Air does not find a valid RF signal on its startup channel, the ProMini Air 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 ProMini Air does NOT find a valid RF DCC signal on its startup Channel from another wireless DC transmitter.

If the ProMini Air 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 ProMini Air’s Channel search process will be unchanged: trying 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 ProMini Air DCC transmitter and receiver to provide a low-cost alternative with a set of features not entirely found in commercial offerings.

You are provided with a few additional components when buying a ProMini Air receiver or transmitter. In the case of the ProMini Air 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 ProMini Air transmitter with power and DCC packets to transmit, so no additional power supply is necessary.

For the ProMini Air receiver, we include a low-cost “DCC amplifier” that converts the ProMini Air receiver’s 5V logic DCC back to DCC. The onboard DCC decoder would, in its typical configuration, pick up from the track (again, discussed in detail below). The ProMini Air 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.

ProMini Air transmitter connections
ProMini Air receiver connections

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 ProMini Air 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 ProMini Air transmitter and receiver is available here.

Kit Assembly

We no longer offer the ProMini Air as a kit.

Firmware Installation

The ProMini Air 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

Depending on whether 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” and no 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 are the following:

  1. Remove the transceiver daughterboard and the jumper (if inserted).
  2. Connect the USBtinyISP (or other) Programmer (with power switch ON to supply 5V DC to the ProMini Air PCB while programming) to the 6-pin connector on the ProMini Air.
  3. From the Arduino IDE, Select Tools → Programmer → “USBtinyISP” (or whatever ISP programmer you use).
  4. Select the AirMiniSketchTransmitter sketch.
  5. Select Sketch → Upload using a Programmer.
  6. 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 ProMini Air receiver or transmitter firmware is installed in the Pro Mini and inserted into the ProMini Air PCB, the ProMini Air is ready for integration!

Integration

To complete the integration of the ProMini Air receiver (Rx) or transmitter (Tx), you must establish several connections.

Overview of Connections

See the picture below for an overview of the connections to and from the ProMini Air. Which connections you use depends on whether the ProMini Air 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 ProMini Air immediately if you reverse the GROUND and POSITIVE POWER SUPPLY connection!

Data and power connections for PMA Rx
Data 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.

ProMini Air antenna connector (female RP SMA) and transceiver DCC input/output

The ProMini Air has several connections that provide AVR programmer, I2C display outputs, and 5V logic DCC inputs or outputs. See the photo below.

ProMini Air connections for AVR programmer, I2C display output, and 5V logic DCC input or output

We will break down these connections for the ProMini Air receiver and transmitter in the following two sections.

Receiver Connections

Starting with the ProMini Air configured as a receiver (Rx), several options exist for providing power. 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.

ProMini Air 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.

ProMini Air receiver powered by an external +5V power supply (older PMA version, but the connections are the same for newer versions)
Close-up of ProMini Air receiver power connections to an external +5V power supply (older PMA version, but the connections are the same for newer versions)

The ProMini Air receiver must connect to an external DCC amplifier that converts the 5V logic DCC from the ProMini Air receiver to DCC A/B that a DCC decoder requires. This DCC amplifier uses battery power and the inputs from the ProMini Air 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 ProMini Air receiver

Some DCC amplifiers have their specialized connector configurations, as shown below, for a GROVE-compliant amplifier.

Example of another DCC amplifier’s connections to the ProMini Air receiver

Integration of the ProMini Air Receiver into a Locomotive

Of course, the real purpose of the ProMini Air 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. This Cytron MD13S amplifier is the one we provide with the ProMini Air receiver unless determined otherwise for size constraints. 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.

ProMini Air 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

Now, let’s turn the ProMini Air 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 ProMini Air transmitter. These outputs provide the ProMini Air 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 ProMini Air receiver connections to a “DCC Converter” PCB that supplies the ProMini Air transmitter with Ground, +5V power, and 5V logic DCC. The ProMini Air transmitter does NOT connect to a battery and does NOT use the jumper connecting +5V to +5V (Battery)!
Close-up of ProMini Air 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 ProMini Air 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 ProMini Air 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 ProMini Air transmitter, we strongly urge you to use the FCC/IC-approved Anaren “whip” antenna supplied with the transceiver that is surface-mounted 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 ProMini Air transmitter online from many sites for experimentation purposes. For fixed installations of the ProMini Air 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 better gain than the ANT-916-CW-HWR-SMA at the expense of being 42% longer.

For the ProMini Air receiver or the ProMini Air 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 ProMini Air 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.
ProMini Air receiver/transmitter connections to an I2C LCD (older PMA version, but the connections are the same for newer versions)
Close-up of ProMini Air receiver/transmitter connections to an I2C LCD (older PMA version, but the connections are the same for newer versions)

The ProMini Air software automatically searches for a valid LCD I2C address on boot-up. Please make sure you connect only ONE display to the ProMini Air.

You can also change the ProMini Air’s DCC address using the throttle’s “OPS” mode. For the transmitter, you use the DCC throttle that connects to the ProMini Air transmitter (by default at DCC address 9900 (previously 9000)). For the ProMini Air receiver, you use the wireless DCC throttle transmitting to the ProMini Air receiver (by default at DCC address 9901 (previously 9001)). The EEPROM permanently stores the changed address, but this new address is not operative until you power cycle the ProMini Air.

Configuration and Testing

We default-configured the ProMini Air 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 ProMini Air 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 ProMini Air 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 ProMini Air receiver will change to Channel 0 and wait for a valid RF DCC signal. This channel change is not permanent, and on a restart, ProMini Air will revert to its default channel.

Several other configuration options are available through “OPS” mode programming, as described in the ProMini Air Users Manual.

We strongly urge the user to test the ProMini Air before the final deployment. At the least, an inexpensive I2C LCD can be purchased here or here (and numerous other locations) to gain some insight into the ProMini Air’s state. This display is particularly beneficial when using the ProMini Air 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 ProMini Air 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 ProMini Air used as a transmitter (as discussed in the next section)!

On the LCD, “My Ad: #” is the DCC address of the ProMini Air 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 ProMini Air receiver. The yellow signal on the oscilloscope is from the T/R DCC output pin on the ProMini Air 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 ProMini Air.

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 ProMini Air 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 ProMini Air’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. The PMA injects DCC IDLE messages when DCC filtering is off (Filter: 0).
No valid RF DCC. The random pulses produced by the RF receiver are reproduced by the output DCC. This is what Gwire and Tam Valley Depot receivers produce.

The user can reconfigure the ProMini Air 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 ProMini Air receiver’s address (“My Add: #”).

Set DCC filtering “on” by selecting the ProMini Air’s address (9901 in this case). Note that the MSG address now matches ProMini Air’s address.

Change CV246 to “1” in OPS mode, which will turn “on” the ProMini Air 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 ProMini Air receiver firmware detects “bad” waveforms that do not appear to represent a valid DCC packet. The ProMini Air 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, then 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 changing back to the locomotive’s DCC address will now set DCC filtering to “off.”

You can repeat selecting the ProMini Air’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 ProMini Air receiver.

Now, when no valid RF DCC is received, the ProMini Air receiver injects DCC IDLE messages amplified by the DCC amplifier and sent to the decoder.

Transmitter Testing

We now turn our attention to testing when using the ProMini Air as a transmitter.

With the same ProMini Air, 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 ProMini Air transmitter (the PCB on the left).

The display will alternate between showing the ProMini Air 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 ProMini Air transmitter’s ID.
The LCD alternately displays the throttle’s address and the ProMini Air’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 ProMini Air transmitter. Since the wireless DCC must keep the Airwire RF receiver “happy” with numerous DCC “IDLE” packets, the ProMini Air 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 ProMini Air 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 ProMini Air in OPS mode.

Once we have changed the throttle’s DCC address to 9900, note that the message address (“Msg Ad: #”) now matches the ProMini Air’s address (“My Ad: #”).

The display now indicates that the message address matches ProMini Air’s address.

For example, while in OPS mode, changing CV246 to “6” will reset the ProMini Air transmitter’s Power Level to 6, as indicated by the display shown below.

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 ProMini Air 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 ProMini Air 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 ProMini Air’s address.

Conclusion and Further Information

The ProMini Air is an inexpensive and hopefully fun introduction to wireless DCC control of your model railroad locomotive!

Please contact the author on this site to purchase the ProMini Air receiver or transmitter. The cost for the ProMini Air transmitter or receiver (with their additional DCC Converter or DCC amplifier and wiring harness) is only $50.00 + shipping.

 

Using the NCE D13DRJ Wireless Decoder with the ProMini Air Transmitter

Introduction

The NCE D13DRJ, now, sadly, discontinued, is a dead-rail DCC decoder that originally touted compatibility with the Stanton Cab. You can find the decoder’s documentation here. The following is a description from NCE’s website (some of the information may not be accurate):

Dimensions: 1.30 x 0.640 x .285 inches – 33 x 17 x 7.5mm

Direct Radio Wireless DCC decoder operating at 916.50 MHZ [916.48MHz]

Features of this decoder: Built-in radio compatible with the S-Cab by Stanton Wireless, Equipped with NMRA 9 pin DCC ‘Quick Plug’ Torque Compensation for ultra smooth low-speed performance. Motor rating 1.3 Amp continuous, 2 Amp peak (stall)  All four function outputs have lighting effects generators. Select from 15 different lighting effects. Full support for LED lighting.

The D13DRJ is designed to be used with Stanton Wireless A.K.A. S-Cab since he uses the exact same wireless chip and frequency we use 916.50 [916.48MHz] MHZ. Tam Valley claimed that even though the receiver they use is 916.37 that it would work fine. We had to find someone with a CVP T5000 for compatibility testing. Originally we relied on CVP’s claim of compatibility but have found that it is not true. [This statement is not entirely correct. See comments below.] We have changed our website and documentation to reflect this.

Examination of the NCE D13DRJ revealed it uses the same receiver chip (the Linx RXM-916-ES operating at 916.48MHz) as the older Tam Valley Depot Mk III receiver, which I previously verified works with the ProMini Air transmitter (PMA Tx) on Airwire Channel 16 (916.37MHz). So, I was optimistic that this decoder would work the PMA Tx.

NCE D13DRJ with Linx RMX-916-ES transceiver operating at 916.48MHz

Using the ProMini Air Transmitter to Control the NCE D13DRJ

The photo below shows the PMA Tx connected to a Digitrax DCS52 controlling locomotive #4291. I set the PMA Tx to transmit on Channel 16 by placing the DCS52 in ops mode at address 9900 and then changing CV255 to 16. After exiting ops mode, I set the loco address back to 4291. 

The ProMini Air transmitter connected to the Digitrax DCS52 set at DCC address 4291

Simultaneously, the Digitrax LNWI, connected to the Digitrax DCS52 via Loconet, receives commands from the iPhone WiThrottle app controlling locomotive #3 (the default address for the NCE D13DRJ).

The PMA transmitter is sending commands to the DCS D13DRJ on DCC address 3

Below is a demonstration that the NCE D13DRJ receives commands from the PMA Tx using DCC commands from the iPhone’s WiThrottle. While it’s difficult to discern the motor’s turning, the accelerations/decelerations when changing direction are easy to observe.

The iPhone WiThrottle app sends DCC commands to the Digitrax DCS52, which in turn transmits DCC commands to the DCS D13DRJ via the ProMini Air transmitter on Airwire Channel 16

Conclusion

The PMA Tx is demonstrably capable of controlling the NCE D13DRJ. While NCE has discontinued the manufacture of this decoder, it is frequently available on eBay and is an excellent dead-rail decoder option for smaller scales.

PostScript: A Note about Airwire Compatibility

The CVP Airwire T5000 transmitter (and presumably all other CVP Airwire transmitters) partially works with the NCE D13DRJ on Airwire Channel 16: speed and direction control work reliably, but the function keys do not operate consistently. The cause for this behavior is unknown; I have never encountered this kind of incompatibility before.

Assembling the ProMini Air Receiver/Transmitter

This page is obsolete. Please see this page.

 

Dead-Rail Transmitter/Receiver Options and Installation

Numerous wireless RF transmitter/receiver (Tx/Rx) options for locomotive control are available both 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, and 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 it’s miles better than no standard at all. 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) band as well (see BlueRailDCC), but I have no personal experience with this band. Another advantage of the 902-928 MHz ISM band is that there is some interoperability between transmitters and receivers, although there is currently no firm standard behind this interoperability.

DCC-compatible Tx/Rx options are a very large 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 loss of valid RF signal from the transmitter is discussed here.

CVP Airwire

A CVP Airwire CONVRTR-60X wireless DCC-compatible RF receiver mounted to the side of the tender hull 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 that include hand-held wireless DCC-compliant throttles (such as the T5000 and T1300) and receivers, such as the CONVRTR series that seamlessly connects to DCC decoders onboard the locomotive. As a general comment, CVP provides excellent, detailed installation and operation documentation, and that’s in part why 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, that are 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 a large number of DCC Idle packets. 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 ProMini Air, 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 ProMini Air 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 available as well 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 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, you must place this wire outside any metal shell, 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 and 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 to external antennas outside of 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 there is no DCC signal available.

Tam Valley Depot DRS1, MkIV receiver with U.FL connector.

Blueridge Engineering ProMini Air Receiver

ProMini Air receiver/transmitter

The inexpensive ProMini Air receiver kit presents no issues when used with 902-928 MHz ISM DCC-compatible transmitters. It operates on Airwire RF channels 0–16 and requires a separate, low-cost amplifier (e.g., the Cytron MD13S) to convert the ProMini Air’s unipolar 5V DCC to bipolar DCC that provides sufficient power to the decoder. See the Blueridge Engineering web page for details on how to build the kit and properly connect the ProMini Air to the amplifier that is in turn connected to the onboard DCC decoder.

The ProMini Air’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 Blueridge Engineering ProMini Air transmitter.

CVP Airwire Transmitters

The CVP Airwire T5000 and T1300 transmitters are excellent choices for operating with 902-928 MHz ISM DCC-compatible receivers, all of 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 Blueridge ProMini Air 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.

Blueridge Engineering ProMini Air Transmitter

The ProMini Air transmitter with optional LCD. The antenna in the picture was replaced with a high-quality 1/2-wave antenna Linx ANT-916-OC-LG-SMA antenna from either Mouser or Digi-Key for improved transmission.

Blueridge Engineering provides the ProMiniAir transmitter/receiver kit 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 Blueridge Engineering) and transmit the “logic-level” DCC on Airwire channels 0-16.

The ProMini Air 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 transmission on Airwire channels 0-16 ensures that the ProMini Air transmitter is capable of communicating 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 ProMini Air, which is 9000 by default. An optional LDC display can be attached to the ProMini Air transmitter for status display. More configuration information is available at the GitHub AirMiniTransmitter site.

Full disclosure here: I am one of the contributors to the AirMiniTransmitter open-source software, and I am heavily-involved with Blueridge Engineering with the design of the ProMini Air transmitter/receiver board.

Dead-Rail Conversion of an MTH 2-8-8-8-2 Virginian Triplex

Introduction

This post describes my most difficult dead-rail conversion to date: an MTH O scale 2-8-8-8-2 Virginian Triplex (MTH product number 20-3101-1) that I purchased on eBay circa September 2019. Previously, I converted a Sunset 3rd Rail Allegheny with an MTH Proto-Sound 3.0 board to dead-rail, but the Triplex was my first complete dead-rail conversion of an MTH locomotive to 2-rail operation, which included lathe turning high-profile wheels to approximate an NMRA RP-25 flange profile (also see NMRA standard S-4.2) so that the locomotive would operate reliably on track meeting NMRA standard S-3.2.

Box details
Locomotive side view
Tender side view

The inside view of the tender below demonstrates a significant challenge: space is very tight with the Proto-Sound board and the large speaker consuming a large part of the tender’s internal volume where we need to install additional dead-rail components: DCC-compatible RF receiver; 14.8V LiPo battery; and switch, charging, and antenna wiring.

Inside view of the tender: Note the battery cradle, the space-consuming speaker, and the end-of-tender smoke unit.

The strategy starts to emerge:

  1. Replace the Proto-Sound 2.0 (PS2.0) board with a PS3.0 board that can operate in DCC mode.
  2. Remove the original rechargeable battery and its cradle and locate the 14.8V LiPo battery pack there.
  3. Remove the large speaker and replace it with a smaller 4-ohm speaker so that we can make room for the 14.8V LiPo battery pack and the Airwire CONVRTR-60X DCC-compatible RF receiver that operates in the 902-928 MHz ISM band on Airwire channels 0-16.
  4. Lathe down the high-rail wheel flanges to approximate an NMRA “RP-25” profile for 2-rail, dead-rail operation.

An advantage of this strategy is retaining almost all of the control the PS2.0/PS3.0 provides, including directional head/tail lamp, marker lights, cabin lights, flickering firebox, sound, and fan-driven smoke units.

Proto-Sound 3.0 Conversion

The first step of the dead-rail conversion was easy: replacing the Proto-Sound 2.0 board with a Proto-Sound 3.0 (PS3.0) board from Ray’s Electric Trainworks. As I have mentioned in other posts, working with Ray Manley is a great pleasure. I sent my PS2.0 board as a trade-in to Ray, and he took care of the rest, providing me with a fully-functional PS3.0 board, complete with DCC capability.

The heatsink for the PS3.0 board necessitated drilling and tapping a new mount hole with spacer, as shown in the figure below.

New Proto-Sound 3.0 heatsink mount with a spacer.

The following photos show the original electrical power inputs to the PS2.0 board and their modified connections for the replacement PS3.0 board.

Original power connections to the Proto-Sound 2.0 board.

As you can see below, the AC power from the center rail pick-up (hot) and the outside rails (ground) were disconnected – we will be getting our power from a 14.8V LiPo battery pack in the tender. In this case, there is no Constant Voltage Unit, so no Battery +(14.8V)/Battery -(Ground) connections are required.

Locomotive power connection modifications. There is no Constant Voltage Unit in this locomotive, so the B+/B- wires indicated above are NOT used.

The AC power connections in the tender are also disconnected, and the power inputs to the PS3.0 connect to the switched battery power. The Battery +(14.8V)/Battery -(Ground) connection on the wiring harness was NOT required.

Tender power connection modifications. There is no need for B+/B- power supply to the locomotive.
Power input modifications for the PS3.0 board. The DCC A/B input power comes from the connection to the Airwire CONVRTR-60X DCC-compatible RF receiver.
Final wiring connections

Locomotive Electrical Modifications

There were two aspects to the electrical modifications in the locomotive:

  1. Headlamp replacement
  2. Electrical power supply

The original headlamp was a power-hungry incandescent bulb. An LED with a polarity-independent plug from Evan Designs was used to eliminate the need to determine the polarity of the original headlamp wiring.

Headlamp LED replacement details

The power-related modifications consisted of removing the center-rail pick-ups, which is very easy on MTH locomotives and disconnecting any wiring to the center-rail pick-up (hot) and the outside rails (ground).

The original center-rail pick-ups. The “Center-Rail Pick-up” is disconnected.
The center-rail connection underneath the motor is disconnected

Battery Installation

Battery installation was very challenging since the only practical placement location was the original rechargeable battery and its cradle mounting beside the PS2.0 board. A special-order 2x2x1 14.8V, 2600mAh (38.48 Wh, 5A rate,  LxWxT: 133 mm x 40 mm x 25 mm) LiPo battery purchased from Tenergy.com provides the one cell-diameter thickness required to fit the battery pack between the PS3.0 board and the tender hull.

Original rechargeable battery and cradle location. The speaker volume control potentiometer was moved to accommodate the more extended 14.8 V LiPo replacement battery pack.
Volume control potentiometer. It was moved from its original location, and UV glue provides stress relief to prevent breakage of the very fine wires.
Final location of the volume control potentiometer. UV glue holds the potentiomenter in place.
Final battery location. Velcro attaches the battery to the side of the PS3.0 board.

Mechanical Modifications

In MTH steam locomotives, the wheel axles insert into a solid cast chassis frame, so the driver wheels must be pulled off the axle before machining the high profile wheels to approximate an RP-25 profile that is compatible with two-rail, dead-rail operation.

The driver wheels must be pulled off the axle for machining after removal of the side-rods. The axle and wheel are scribed to maintain proper “quartering.”
A wheel puller to separate the driver wheel from the axle.
Comparison of lathe-cut and unmodified high-profile wheels. The high-profile flanges were lathe-cut to approximate an RP-25 profile for 2-rail, dead-rail operation.

Tender Mechanical Modifications

The tender’s mechanical modifications involve adding a Kadee 740 coupler and accommodating additional dead-rail electronics.

Coupler Modifications

The original coupler pivot, rather than using a frame-fixed mounting, was used to mount a Kadee 740 coupler. This strategy ensured that tight curves would not bind the coupler.

The original coupler assembly

A Kadee 740 coupler was mounted on the original coupler pivot, as shown in the Figure below. The brass screw heads were ground down to provide clearance with the tender frame.

Modified coupler assembly for a Kadee 740 coupler

Additional Dead-Rail Electronics

The added dead-rail electronics include the charging plug, the ON/OFF/Charging plug, a smaller speaker, and the antenna mount.

Charging plug (left) and ON/OFF/Charge switch (right) mounting
Antenna mounting location. The antenna is a  Linx ANT-916-CW-RCS discussed in this blog.

The original speaker was far too large to provide clearance for the additional battery, DCC-compatible RF receiver, and other electrical components needed for the dead-rail installation. So a 16mm x 35mm speaker was placed in the bottom of the original speaker’s cavity, and UV glue holds the speaker in place.

The original speaker. It is far too large to accommodate the additional dead-rail components: battery, DCC-compatible RF receiver, ON/OFF/Charging switch and charging plug.
Candidate speaker. The actual 16mm x 35mm speaker was even smaller and mounted into the bottom of the original speaker cavity.

Final Demonstration

With the locomotive reassembled, it’s time to test it out! If your locomotive has a smoke unit(s), always ensure sufficient smoke fluid is loaded. Even if you don’t intentionally turn on the smoke unit – sometimes it’s unexpectedly activated.

 

Initial demonstration

General Battery Issues

Introduction

One of the most vexing challenges for me when doing dead-rail conversions on O scale steam locomotives is what battery to select. As nearly as I can determine, lithium polymer (LiPo, see LiPo Wikipedia) batteries are the almost-universal choice among dead-railers. So, the choice of battery technology was not much in question for me, but the battery voltage and size is still a choice to be made. I’ll deal with each of these in turn.

Battery Configurations

I’m not sure how I fell into the 14.8V “camp” for LiPo batteries on O scale dead-rail conversions. Maybe it’s because CVP pushes them for their Airwire products (CVP Airwire). I think CVP has valid admonitions about using higher voltages in regards to radio control range performance and cooler operation (see for instance CVP G3 Decoder User Guide, page 12). And, and almost all of the O scale operating modes (2 rail DC, three rail AC, TMCC, DCS) seem to have 24V or so maximum operating voltage, which is getting close to damage threshold for some radio receivers such as the CVP Airwire receivers. So, would 11.1V (3 LiPi cells in series, “3S” as discussed later) work? Probably just fine in most cases. The plus for 14.8V LiPo is that vendors offer a variety of battery physical and power configurations at 14.8V, which I’ll address next.

There is probably a good deal of lore and religion surrounding the specifics of which brand and configuration of LiPo battery to choose for dead-rail. I’m going to try to stick with what I have tried, not what might theoretically be “better” or “worse.”

Let me start with the less controversial part of my decision process: configuration. LiPo batteries come in a large variety of sizes and configurations (see for instance this site), but in my personal experience with dead-rail, the LiPo’s seem to have a single cell size roughly that of an AA cell with 3.7V output with a charge capacity of around 2000 to 2600 mAh. The individual cells are connected to achieve a total output voltage of about 14.8V (four connected in series, thus the term “4S”), but what varies is the total charge capacity and its ugly handmaiden – physical size.

This is the bear: We want large charge capacity for longer running times, but we in O scale must fit the batteries in often-tight spaces (at least compared to G scale) such as tenders where we also put radio control receiver boards, sound cards, speakers, etc. Of course, HO scale has even more severe volume constraints, but with approximately one-sixth the mass the locomotives must pull.

Personal experience here: I tried to fit an eight-cell (two rows of four vertically-stacked cells, 2.6″ x 2.8″ x 1.4″, 6000mAh, CVP BATT2) configuration into several O scale tenders, and that battery pack just flat-out would not fit. Even though this configuration was only one cell high, O scale tenders are just not tall enough to fit even one cell oriented vertically – the cells must lie sideways to fit. This cell-length limitation is important to remember for O scale. You might find space in diesel locomotives, but not steam locomotive tenders. These limitations were a big disappointment for me since I wanted to cram a large storage capacity battery pack in the tender and run “forever” (forever being at least four hours).

Sigh… Backing off in size, I have found that 2x2x1 LiPo battery packs will fit in O scale tenders with the individual battery cells running along the length of the tender. See the Figure below (pardon the body parts). You can see that this configuration also comfortably fits the width limitations of O scale tenders.

two_by_two_by_one_battery
Figure 1: 2x2x1, 14.8V battery configuration that fits. For reference, the CVP G3X receiver board between the battery and speaker is approximately 4″ long.

A note of caution: you cannot stack too much on top of this configuration before you lose vertical clearance inside the tender. For instance, I thought this was going to work:

two_by_two_by_one_battery_stack
Figure 2: This didn’t fit!

Stacking the receiver board on top of the battery would be a useful space-saving strategy, but this configuration would not clear vertically in all tenders I tried (Big Boys, Cab Forwards, Challengers, and Alleghenies). The receiver board manufacturers would probably dislike my mounting electronics on top of batteries, even with sufficient clearance.

Battery suppliers

My experience is confined to three battery suppliers of 2x2x1 LiPo battery packs: CVP, Tenergy, and “HJE.” All come with a Protection Circuit Module (PCM) that provides:

  • Overcharge, over-discharge protection
  • Overcurrent protection
  • Short-circuit protection
  • Voltage- and current-balance
  • Temperature protection

Suppliers:

Recent experience

Example of a 1x2x2, 4S1P (4 Series, 1 Parallel) battery configuration (from Tenergy.com) on a dead-rail install of a PS3.0-equipped (w/ DCC operation) MTH Virginian Triplex. This battery configuration reduced the thickness sufficiently to fit alongside the PS3.0 board where the original PS2.0 battery pack was mounted. The PS3.0 replacement board was obtained from Ray’s Electric Trainworks.

More creative 14.8V battery configurations are possible that include one battery-diameter thickness solutions such 1x2x2 (Tenergy.com) with dimensions of 131 x 36 x 23mm (LxWxT), so it’s approximately one battery-diameter thickness, two battery-diameters wide, and two battery lengths long (~5.2″). See the picture above for an example of using this thin configuration in a very tight mounting configuration on an MTH Virginian Triplex with a PS-3.0 board operating in DCC mode. See this blog for more details.

Dead-Rail Conversion of a Sunset 3rd Rail Allegheny 2-6-6-6 Locomotive with MTH Proto-Sound 3

Introduction

Don’t jump to conclusions; MTH did NOT manufacture the C&O 2-6-6-6 Allegheny with MTH Proto-Sound 2.0 (PS2.0) I found on eBay. Instead, it’s a brass locomotive produced by Sunset 3rd Rail (Figure 1) and converted to PS2.0 (see MTH PS2.0 Upgrade Manual). See Figure 2. The retrofit replaced the original tender QSI-OEM Digital Soundboards, the wiring harnesses for the tender and locomotive, and the Suethe smoke units and their voltage regulator board in the locomotive.

Sunset_Allegheny_Box_End
Figure 1: Sunset 3rd Rail C&O Allegheny box info
Allegheny_PS-2_Tender_Board
Figure 2: Original tender Proto-Sound 2.0 electronics and harness wiring

It was a well-done conversion, so I was very reluctant to tear out the tender PS2.0 control board, and the wiring harnesses in the tender and locomotive. The PS2.0 conversion used an MTH smoke unit that has both fan speed and smoke intensity controls.

Allegheny_MTH_Smoke_Unit
Figure 3: MTH Smoke Unit with funnel

The CVP Airwire receiver boards I typically use for dead-rail conversion don’t have this level of smoke unit control. And, the PS2.0 board used a speed encoder on the locomotive motor’s flywheel to synchronize the PS2.0 board’s sound. See Figure 5 for the speed encoder reader and flywheel strip and 5b for additional electrical connections.

Figure 4: Original Constant Voltage Unit wiring with dead-rail modifications indicated
Allegheny_PS-3_Locomotive_Wiring_Harness_Diagram
Figure 5: Speed encoder, flywheel strip, and electrical connections for the Constant Voltage Unit.
Allegheny_PS-3_Locomotive_Wago_Connections
Figure 5b: Locomotive harness wiring after modifications connecting the Constant Voltage Source to Battery +/- and replacing incandescent bulbs with LED’s

All of these built-in features were pretty nice, but I still wanted a dead-rail conversion.

Hmm… Looking around, I found out that Proto-Sound 3.0 (PS3.0) had DCC/DCS control options and the wiring harnesses are the same for PS2.0 and PS3.0 boards (see for instance MTH PS3.0 Upgrade Manual). Things are looking up. Then I found a great site, Ray’s Electric Trainworks, that provides PS3.0 replacement boards and great support.

My thought was this: if I can upgrade the locomotive to PS3.0, then I can take the following steps. Jumper the PS3.0 board to DCC operation, disconnect the original rail power/communication wiring, and re-connect the rail power/communication wiring to the DCC outputs of a CVP Airwire CONVRTR-60X receiver (CONVRTR Users Guide). Easy, right? Not so fast.

Ray at Ray’s Electric Trainworks was a great help: he steered me to the right PS3.0 card that I needed for the tender, and he loaded the Allegheny sound file for me. Otherwise, I would need a bunch of DCS infrastructure to load the sound file. And, he gave me a rebate for the old PS2.0 card! Great guy.

OK, I have the PS3.0 card from Ray. The PS3.0 card came mounted in its plastic carriage that is screw-mounts on the tender chassis through pre-existing holes. The heatsink orients a bit differently between the PS2.0 and PS3.0 – no big deal – I just needed to drill a hole in the tender chassis in a slightly different place. The PS3.0 doesn’t use a Ni-MH battery, so out it went. That was a good thing, too, since I needed the real estate for the replacement LiPO battery that would supply power to the control boards, lights, smoke unit, and the locomotive.

Locomotive Modifications

Here is a diagram of the locomotive wiring harness from the MTH PS3.0 Upgrade Manual with my annotations.

Allegheny_PS-3_Locomotive_Wiring_Harness_Diagram
Figure 6: Locomotive PS3.0 wiring harness with modifications indicated

Since I wouldn’t be sending track power to the tender, I cut the Ground Lead and Pickup Roller Leads wires. I re-purposed them by connecting these harness wires to the Constant Voltage Unit, which is a heat-shrink blob whose input leads were cut from their original chassis connections (see Figure 5 again).

While I was at it, to reduce power consumption, I removed the incandescent cabin and headlight bulbs, and I replaced them with Yeloglo LED’s (see Yeloglo description) whose + input was in series with the Yeloglo’s 470-ohm resistor for 10-16 Volt operation. Yeloglo LEDs have an excellent yellowish output reminiscent of incandescent light.

Tender Modifications

The diagram below shows the tender’s wiring harness with my modifications.

Allegheny_PS-3_Tender_Wiring_Harness_Diagram
Figure 7: Tender PS3.0 wiring harness with modifications indicated

Continuity testing revealed that the locomotive Roller Pickup Leads and the Ground Lead connected to Pin 1 and 3 of the 7-pin connector, respectively.

Note that BOTH locomotive and tender Ground Leads (both are black) that are input to the PS3.0 on pins 3 and 4 of the 7-pin connector, respectively, MUST BE DISCONNECTED FROM THE LOCO/TENDER FRAMES AND CONNECTED to the “B” DCC output of the CONVRTR. This pair of connections was the trick. I initially connected ONLY the Ground Lead coming from the locomotive (pin 3 of the 7-pin connector) to the CONVRTR, and it did NOT work! I don’t know if only connecting pin 4 of the 7-pin connector would work – I didn’t try it.

Similarly, I disconnected the red wire that is input to the PS3.0 on pin 1 of the 7-pin connector (which originally connected to the locomotive Roller Pickup Leads) from the plug bundle that connects the tender to the locomotive, and I connected it to the “A” output of the CONVRTR.

The “harness side” of the two cut wires originally going to the Pickup Roller Leads (red) and Ground Lead (black) on the locomotive, were connected to switched Battery + and Battery – (ground), respectively, to provide power to the locomotive’s Constant Power Unit.

Note: “Switched B+” means battery power coming from the Battery’s + terminal that is turned on or off with a switch (you want to be able to turn off the power!). “Battery – (ground)” means the connection to the Battery’s negative terminal that is usually grounded to the tender chassis by a battery charging plug.

A picture is worth a thousand words, so studying Figures 6 and 7 will give you the story of what wiring cuts and re-connections are needed to convert a Proto-Sound 3.0 steam locomotive to dead-rail.

Other Dead-Rail Conversion Details

Of course, there are other aspects to the dead-rail conversion that are required. These aspects include the addition of battery power and CONVRTR connections and removal of center-rail pick-ups and electrical connections that are part of a typical 3-rail to dead-rail conversion for an O scale steam locomotive. These conversion aspects are discussed in another blog.

Wrap-Up

In summary, if you have a locomotive with the PS3.0 installed, conversion to battery-powered DCC operation and radio control (dead-rail) is straightforward once you know the few wiring cuts and re-connections you need to make. The DCC operations for this particular locomotive can be found in the MTH document “Premier 2-6-6-6 Allegheny Steam Engine .” What you preserve with the PS3.0 is good DCC functionality, the original sound, and coordinated smoke – and that’s a pretty nice combination.