On 9/27/06, Roy wrote: > Ok have changed my circuit to the attached version. > > Let me know why this would not work :-)) > OK. Say Target is pulling low. U2 is "on". The phototransistor in U2 turns on the diode in U1, which turns on its phototransistor, pulling Target low. This is fine, right? Target was low anyway. But when Target tries to change and go high, it will be pulling directly against the transistor in U1. Ouch! Regards, Mark markrages@gmail -- You think that it is a secret, but it never has been one. - fortune cookie -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist