stan2004 posted:rtr12 posted:...Also tried a 3906 for the PNP. I don't really think this matters much though? I think it's the shortage of voltage output on pins 3 & 9 of the 556 exactly as you suspected.Right. Well, if you're still determined to get circuit 2 working, try the following simple change:
Ditch the 2N3906 and use a 4th 2N3904. The objective is to turn OFF the Green 2N3904 when either Red or Yellow is high. In the circuit on the right, the "new" 2N3904 turns "on" when either Red or Yellow is high. When this 2N3904 turn on, its collector voltage (which drives the Green 2N3904) drops to 0.2V (or less). This 0.2V (or less) is insufficient to turn on the Green 2N3904 and hence it turns off. The relevant datasheet info is the so-called "Collector Saturation Region" which we can get into if you really have nothing better to do with your time but it does get a bit nerdy
- I figure you ought to be able to prototype this with actual hardware in a couple minutes which would be more expedient!
Well I couldn't stand the suspense so I tried this out after supper. Works like a charm Stan. And now the green led is either on at full current, or completely off. No dim flickering when red or yellow is on, or anything foolish. 
So thanks to your help Stan we can now call this variation a win!
Rod
