Re: Optocoulped Parallel port

> You don't use the pullup resistor to power the optocoupler. You use
> either the PC
> power supply or an external +5V power supply, through a resistor,
> through the
> LED or optocoupler, and finally to the port output, which will light the
> LED when
> the output is at logic ZERO, or grounded. More current is available
> that way.
> This all applies to output from the PC to external devices.

I would agree, however if you are trying to plug into the parallel
port and the parallel port only, and not have an external power
supply, then you have to use the port as a current source rather than
sink. Which is marginal, but tends to work.

Chris


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Christopher C. Stratton, stratton@...
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