At 08:49 PM 7/16/2009, Jinx wrote: >Picked up my H11D1 optos for Figure 3 at > >http://www.rory.co.nz/projects/lighting/beat_strobe.html > >and been trying, unsuccessfully so far, to get a flash out of it > >The problem appears to be that the SCR gate rises to only 200mV >when the opto is activated. Looking on the scope there don't seem >to be any gate pulses higher than 200mV and no activity at all on the >cathode. Voltage on the cold side of the 2k2 (opto collector) also >drops to near-zero It sure sounds like something is funky with the opto. Try removing the opto from the circuit, then measure the voltage across the SCR. It should be somewhere between 50 - 100 Vdc. If so, momentarily short the leads that used to connect to the opto output - the strobe should flash. If that does happen, look for problems with the opto. Transistor wired backwards? Too much leakage? If all else fails, do consider trying a MOC3011 instead of the opto you are currently using. Like I had mentioned earlier, I've built MANY strobes using the MOC3011 as the trigger element (it replaces the SCR). All still working to this day. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist