Locomotive Motion Detection Circuit (revisited)

Looks like you have another good idea going here and have made it work on a really small board as well.

Very nice.  Now you can get back to the real world with a solution to remote-control of rolling stock.

Out of curiousity, why 0.1uF and before the 330?  I'm not familiar with TMCC engine electronics, but for modern PWM motor drive electronics running at, say, 20 kHz that's an impedance of 80 ohms so I'm thinking that cap is not long for this world.

Stan, much of the TMCC stuff has a 1uf 50V capacitor across the motor for spike suppression, especially AC motors.  I figured a little protection there was not a bad thing for the motors that don't include it.  It's probably not necessary, but it's a belt-n-suspenders kind of thing.  Interesting point about the PS/2 motor drive, I didn't consider that.  I'll have to put one of these on a PS/2 locomotive and see what happens.  I could also just leave it off, I doubt the opto-coupler will mind the PWM.

I found that the little relays came in a heavy-duty version, so these have 5A contacts.  However, I only got 11, and it seems these are suddenly popular and everyone is out of not only the 5A version, but the 2A version as well.

I still don't know what will become of this in the long term.  It's a handy capability, but it's fairly expensive to tool up to get any quantity made, and I'm not sure there would be that much interest.  I figure I'll at least have some for my own use.  Hand building these is somewhat time consuming, so unless I could justify a larger quantity, I'll only have a limited number.

I'm still thinking of a more all-encompassing diesel board that will have serial data capability and do all of this and more.  Obviously, that's a larger project, but it would be cool.

I ordered the parts to test the EMI filter for the MP3 module with the RF receiver, that will be an interesting experiment.  If that goes well, I'll probably crank one of those out.  I also have a slightly different MP3 module coming that is the same form-factor but it has a 64MB FLASH on-board for the audio files.  It has a slightly different pinout, so I may look into a jumper option to use either one on an RF audio module. 

I did order half a dozen boards for the MiniCommander MP3 player design, that one has worked well plugged together on the bench, so I figured it was ready for some fiberglass.

So many projects...

We're good.  I was just curious since I figured if it was for hi-freq suppression it would (already) be on the motor, if for low-freq LED current limiting if would already be done by the motor drive bridge to protect the transistors, if for smoothing you already have the cap across the FET gate, etc. 

Yes, onward to the next project!

The cap is from my days of overdoing EMI protection in aerospace.  Too bad I never dealt with class-D amplifiers, I'd have known what to expect.  Truthfully, I don't ever remember any sound generation at all in all my years, just a few beepers and a rather loud OEM horn for altitude warnings.  I wonder what the systems that have the voice output use, never checked.  I suspect the high EMI is probably why I never encountered any class-D amplifiers in my avionics career.

I'll let you know if the filter has the right effect on the sound outputs.  I'm planning on connecting it right to the board pins to minimize the exposed wiring.  Hopefully, cutting that emission down will help with the RF range while audio is playing.