Above is the basic diagram of the system. The T5000 transmits DCC over the air. The AirRx picks up that signal and passes it out the ‘D’ output pin on the receiver. This is the logic level DCC signal. To use this to drive a standard decoder, it needs to be ‘boosted’ up to a higher voltage. In G scale, this is typically 14.8v which corresponds to a 4 cell Lipo pack. The booster is actually a motor driver which follows the DCC logic signal but at the battery voltage. The Cytron booster will provide up to 10A of power, more than enough to drive any large scale decoder on the market.
While the above diagram shows the basic components, you will want to connect the power wires to a DPDT switch between the recharge jack and the battery. Flipping the switch one way connects the battery to the recharge jack and shuts off power to all of the components. Switching it the other way powers up all of the components and turns on the locomotive. See below.
Configuring the AirRx
Basically, the AirRx works ‘out of the box’ if you are just using the DCC output. The signal from the T5000 is passed unchanged out to the ‘D’ output pin. If you wish to use the servo or digital outputs, you will need to configure the Receiver. The Receiver is also technically a ‘multi-function decoder’ on it’s own. It listens to the signal it is passing out to the ‘D’ pin and looks for commands to it’s own internal DCC address. If it matches, it performs various functions depending on how it’s configured. You can configure the device using the ops mode function of the T5000. The following map shows all of the CV addresses and values:
/* * Decode message packets here and do servos and config variables * * CV 201 - Radio Channel 0-15 * CV 202 - DCC Address lo * CV 203 - DCC Address hi * CV 204 - Servo Mode 0=Steam, 1=couplers, 2=ESC * CV 205 - Servo0 LowLimit Lo * CV 206 - Servo0 LowLimit Hi * CV 207 - Servo0 HighLimit Lo * CV 208 - Servo0 HighLimit Hi * CV 209 - Servo0 Reverse * CV 210 - Servo1 LowLimit Lo * CV 211 - Servo1 LowLimit Hi * CV 212 - Servo1 HighLimit Lo * CV 213 - Servo1 HighLimit Hi * CV 214 - Servo1 Reverse * CV 215 - Function Code for Coupler 0 * CV 216 - Function Code for Coupler 1 * CV 217 - Function Code for Output x * CV 218 - Function Code for Output y * CV 219 - On/Off Code for Output x * CV 220 - On/Off Code for Output y * CV 230 - Reset to factory defaults */
When you program the above CVs, note that the two byte ones such as the DCC address and the Servo limits need some translation. Take the value you wish to program, say 500 for a low limit on one of the servos. Use something like the windows calculator in ‘programmer mode’ to convert 500 to hex. This will give you 01F4. Take the bottom two digits (F4) and put that into the calculator to find the decimal value. It should give you 244. That will be the low byte. Now take the top digit(s) and convert those. In this case it’s just a 1, so that converts to a 1 in decimal. That is now the high byte. All of the two digit CVs do not actually write the value into the EEPROM until the second digits are written so always program the low byte first and then the high one.
Note that its possible to get the receiver into a state that it won’t respond if you forget the address or the Airwire channel it is assigned to it. If you do forget, you can ground pin two of the processor when you power it up, this will initialize the EEPROM to defaults (same as sending a value to CV230).
Using an Electronic Speed Control
If you don’t need all the extras that a DCC decoder provides and just want a control for forward and backward, you can use an Electronic Speed Control to directly drive the motor in your locomotive or critter. I have had good success with the Pololu 18v7 They also have a newer model for the same price which delivers 15amps Pololu 18v15 Other ESCs can be used, some smaller ones can be had in the $10 range. HOWEVER- the AirRx requires a BEC (battery elimination circuit) that provides 3.3v, NOT 5v. The Pololu controllers can set to either, some others are fixed.
Note that you can also connect two relays to the output of the AirRx. You can assign these outputs to functions on your T5000. For example, the lights or trigger a sound. A good source for relay modules that can be driven with the AirRx is again, Pololu. Their dual 12v relay modules are inexpensive and available as assembled modules or as a simple kit. Pololu Relay Module