I think you have more than one problem. #1) You are not seeing the proper voltages for triggering the SCR. Your opto may be to blame. #2) You are not triggering the flash even when you dump current through the transformer. If you are still interested, I can suggest methods for testing each of these. Gus -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist