Update: I have been experimenting with the trim pot idea suggested by Stan. With R3/R4 values of 100K, a trim pot of 100K seems to work well. I also reduced the C2/C3 values from 22 uF to 10 uF. All seems to work. Flash rate is about 1 Hz; or 2 seconds per complete cycle. That looks about right to my eye.
Interestingly the flash rate seems unaffected by supply voltage difference, at least over a range of 6-12 vdc. The LED brightness is affected somewhat by trim pot adjustment, but not noticeably so. It is more affected by changes in supply voltage of course. Overall it seems like a good little flasher circuit and I have ordered some test pcb's from OSH Park.
As an aside; has anyone got any ideas on how I might be able to use this basic circuit to alternately flash a couple of large 12 volt LED's, say up to 1 amp load? I have this vague idea that I might be able to use the low power alternating S8050 outputs to drive two larger NPN power transistors, say TIP120's or similar. These are rated at up to 5 amps collector current and 65 watts TDH. But I have no idea is this is doable. Appreciate any thoughts.
Thanks, Rod
