The diode would be a good idea... I forgot about that.
57.6K would probably work with the proper selection of resistors, but you could totem pole the opto's to make them pull up and down. -Chuck Harris Bob Camp wrote:
Hi The only other thing I have seen done on opto isolated RS-232 is to add a protection diode on the "transmit" opto output transistor. There's a spec that says you have to be able to apply +/- 25 volts to any pin weather the device is powered up or not. If you want high(er) speed you can put a pair of transistors on the output of the opto to boost the drive current. Not needed at 9600 baud, probably useful if you are trying to go > 100K baud. Bob
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