On Thursday 08 October 2009, cogoman wrote: >LEDs usually have between 1.5 and 2.2 volts at 10mA depending on the color. >Silicon rectifier diodes are the ones that have .6 volts across them at > 10mA. > >| That's because of the sink arrangement. When the EMC2 output is High, >| both sides of the opto-coupler LED are high, so there no current will go >| through the LED. Generally you need around .6 Volts across the LED and >| between 10 to 20 milliamps for normal operation. When the EMC output is >| Low, the minus side of the LED is zero volts (sinking to ground), the >| LED + side is around .6 Volts and the + side of the 270 Ohm current >| limit resistor is 5 Volts. > Agreed, that .6 volts is 100% doofy. Should be, as you state, 1.6 to 2.2 volts at the + terminal of the opto's led. Are they hooked up backwards, and a protective diode is limiting the drop to that one silicon junction drop?
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