Quote:
Originally Posted by nuttle
A couple of other possibilities:
-- Use an analog input, instead of a digital one (via the analog breakout board, I mention this mainly in case someone comes along, reads this, and wants something easy and quick)
-- Use an opto-isolator (this not only level shifts, but avoids potential problems with ground loops -- you probably don't need to worry about this, but it is very good to be aware of and on the lookout for this type of problem)
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An opto-isolator is a splendid idea that will almost always work. Why did someone not already bring it up?!?! Kudos to you

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Using an analog signal would be getting a little off from what we want here. For something like the raspberry pi or propeller would be hard to interface with a DAC/ADC couple. On the RPi, I don't know if you'd even have enough GPIO!