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- Aug 14, 2013
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Ah I did not think of non visible LED-light can I check that with my LPM? would the center likely be the +end?? maybe i should check the continuity at the plug when light shines of the clear lens (?photodiodes?)these have OR MAYBE I take a hammer and see whats inside--
Before resorting to the hammer, there is a way to find out the polarity. You need an
incandescent light bulb. Shine it on the device in question and start probing with the meter.
An LED will give a few mV. A photodiode will give hundreds of mV up to a volt. A
phototransistor won't give anything (I don't think, don't quote me on that). Then when you
think you've got it, put 10-25mA through it, + to +, - to - and it should give light if it still works.
If FP is right, it will be 940nm IR, so you will need a way of "seeing" it.