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Reply to "Home-brew TMCC Control of the MTH Signalman Caboose"

Hi Stan - does that part of the operating reefer just trigger a relay, like in the caboose? The TLP222AF SSR is rated for 500mA, so if that part of the circuit draws less than that it should work fine.

In my case, I used a N-FET to directly drive the DC gearmotor.  A photo of the circuit from the linked article:

reefer remote components

As mentioned, in the MTH operating reefer, one side of the DC gearmotor is connected directly to 9V DC.  So the N-FET simple grounds the other motor terminal for a few seconds to start the operating cycles.  My notes show the DC gearmotor draws about 100 mA when active...so 500 mA is good as the long as the SSR is DC-capable.

The Moteino's I/O pins can source or sink 10 mA at 3.3V (more if you parallel outputs), so you can use them to drive whatever actuator you want, including PWM. I used the SSR because it made the output circuit trivial, but if you wanted more drive (or didn't want to pony up the $1 for an SSR) you could use a transistor or triac instead.

Because the Moteino is powered by the 9V from the MTH electronics, I think is safe to assume if driving a DC motor using the MTH electronics, that you do not need the optical isolation provided by the SSR.  Hence I have the RF receiver logic output pin directly driving the N-FET (i.e., no optical isolation).

If I was going to develop this project further, I think I'd design a series of little shield PCBs you could stick onto the Moteino for different applications. E.g.

  • Powered by DC input or added rectifier/regulator circuit for track-powered.
  • Relay, transistor, or triac output.

Being so small (about 1" x 1"), the PCBs would be very cheap.

I'd also design shields for the master node, to read the TMCC commands from a serial line or the Legacy PDI.  Installing the master node is probably the biggest hurdle for someone else to replicate the system, because you need something to read the convert the RS232 to TTL.

Agreed.  The master node is doing a lot more work than the receiver in the caboose!  In my project the trigger is pushing a button on a fob.  But of course that's another device to keep around.  For DCS command control, I separately showed hooking up an output of an MTH AIU to electronically "push" the button on the fob.  So in a TMCC environment I suppose the equivalent would be to have an ASC or SC2 Accessory controller wires to electronically "push" a button on a remote control fob.

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