Ive been pulling my hair out about this one, Figured Id give the GRM crowd a chance to sort it out instead of a proper electronics message board (you guys like bacon way more).
Ive got this project which requires a midi input to a microcontroller (in this case an arduino cause I am impatient and too stupid for a real micro) that part isn't too important.
What is important is that I am having trouble getting the midi in to work properly, here is the circuit, I am just using the input part in my test rig:
The opto in question is here: http://www.sparkfun.com/commerce/product_info.php?products_id=314
The only resistors I could find in the bin were 280 ohm, which should work. My problem is this: Midi signals get through to the darlington, but it isnt pulling the signal all the way down, only a volt or so. I am measuring between ground and "to UART RxD", the signal is clean and the lines on the scope are nice and flat, MIDI spec is well within the frequency limits of the opto... What the crap!? I feel like such an idiot, this is an easy circuit.
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