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Reply to "Arduino-based throttle control"

Jon1443 posted:

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So my question is, what's the easiest way to go about using the PWM function of the board to control the variable voltage? 

No doubt someone in the Arduino community has worked this out, but if using the triac method as described in the link from the Professor you need to synchronize the "PWM function" to the 60 Hz line frequency.  If by throttle you also mean to support Whistle/Bell, the arguably easiest method is to fire the positive and negative polarities at different times - again synchronized to the 60 Hz zero-crossings.

The CW-80 schematics have been posted many times on OGR so that would show you the hardware side of the triac method driven by a microcontroller (though obviously not an Arduino microcontroller).  But if you're going to do the homework to design an Arduino-controlled throttle circuit, consider how MTH uses 4 FETs (10-cent transistors) instead of a triac in their TIU for the variable channels.  That is, the 4-FET configuration has more flexibility in when/how you turn the voltage on and off in each 60 Hz cycle.  It would be much software than the triac method and you won't find any published schematics of the TIU variable channel - but hardware concept is generic.  Just depends on whether someone else in the Arduino community has already done the homework and posted the how to.  Again, it comes down to expediency vs. building a better mousetrap.  That is, the 4-FET (or its cousins) would be the basis for something akin to the Z-4000 with a smooth sine output rather than chopped/ugly voltage signal from a triac controller.

I get laughed off the stage whenever I show this but I suggest it is food for thought.  If you already have an MTH Z-controller (which is a triac-based throttle with whistle/bell), how about an Arduino driving two 99-cent servos.  As you know there are servo functions in the Arduino library that use PWM outputs making the software trivial.  Here are two videos demonstrating the concept.  There's a bit more info on this hack in the O gauge archive here.

Throttle control:

Bell/whistle control:

99-cent eBay servo (free shipping from Asia):

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