[TriEmbed] Why Did This Stop Working?

[Grawburg]

My train/conveyor project developed a glitch when I redid the protoboard I was using.  The key to the project was an pair of IR LED emitter/detectors (Sparkfun SEN-00241) that until the rework operated just fine when 4.5 inches apart. Both units were inside of 1/2" tubes so that room lighting did not affect them.   Circuit is attached. (I'm using 3.3 VDC)

Now, here's the one change -- and it's actually due to an original mistake.  The schematic shows a 10k resistor going to the collector of the detector. That's what I thought I had used on the original board (the one that worked) but discovered I actually had a 100k. My new board does have the 10k and what is happening is that instead being able to have the emitter/detector work at 4.5" they only work at about 2". Meaning that voltage goes to Vout which is a pin on my MCP23008 port expander when the devices are much beyond 2 inches apart.


Thanks,
Brian Grawburg







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