"Outside the box" solution or absolute stupidity?

[MichaelL65]

OK, unusual situation here. I have a H0-CTRIO in a DL-06 frame. The encoder is open collector, which requires a +V on the common (M) for the CTRIO. However, we are also using a reset signal, which comes from a sourcing device, which would require a GND on the common. Obviously not a ideal situation.

To make this work I had originally made a circuit to convert the open collector signals to sourcing, but we are having a lot of trouble with getting that to work properly (different CTRIO cards will measure different voltages off of the same circuit, sometimes even below the 9V threshold). It was not a good solution.

Here is the hair-brained solution I've came up with (but not wanting to risk frying my module, I thought I would run it by you guys first): If I made the common (M) +12V, that would be able to drive the open collectors of the encoder (A,B) just fine. The reset coming to input D is sourcing at +24V, so it still has a 12V potential to M (The panel is powered with 24VDC, but a handful of components require +12V so there is a regulator to provide that). In theory that should work, but I've been doing this long enough to know theory and reality don't always agree...

So, does this idea risk anything to the CTRIO module itself (would it fry it, cause it to melt down, end civilization as we know it), or is it in fact designed to work this way? Ideas? Comments? Dire warnings?

[BobO]

I ran this by the CTRIO hardware designer and he said it should work peachy. All disclaimers apply and your mileage may vary. 

[Tim]

This is unusual but should work just fine.  The Reset signal return current will actually flow from our common M terminal toward the +12V power supply, but since it's likely a small amount relative to the total draw from +12V, there should be no issue with it's regulation.

Each CTRIO input has it's own full wave diode bridge allowing anything >9V away from the M to generate a guaranteed ON condition.  You've got a MacGyver type solution here using just the signals already available.  Well done.

[MichaelL65]

Great! I might earn my keep yet!

Sorry it took so long to get back here to check your timely answers, but I'm working on 5 major projects simultaneously (oh the joys of a small company ) and had to put this one aside for a bit. The coworker who took over my part of that project just used pull-up resistors like we had before, but I'm still going to try this to see if it works because it will make it a heck of a lot simpler for future versions (and this project needs all the simplifications it can get! ).

If it works as well as I think it should, it would be worth doing a refit on the existing systems.