Rod Stewart posted:Just bread boarded the 3 transistor #2 circuit above. It works quite well, though no better than that shown in R5.4 also above, from what I can tell. I had to change the resistor that grounds the base of the 2N3906 PNP transistor from 10K to 2.2K. The green led was not lighting after the yellow went out, so I reasoned that the base voltage was not close enough to ground with the 10K value to make it conduct. Anyway, it seems to work fine now. I also added a couple of diodes in line with the red and yellow leds, to better equalize the currents and reduce their brightness to more like the green. All good.
Rod
That's it, #2. I wasn't sure that placing the PNP above the Green LED would work without more parts value sensitivity, but it looks good. The 2.2K draws more current from the 556 but it's got a lot available. Alternatively I thought about using one fourth of a CMOS 4001 driving an NPN transistor. The CMOS chip can use any of the voltages being suggested. But the above has less parts.
