A bipolar transistor version of the astable multivibrator with a yellow Pirhana LED required absurdly large capacitors for a reasonable blink rate and, seeing as how I need a demo circuit for Show-n-Tells, it seemed a good candidate for a faster blink. I replaced a 100 µF cap with the 22 µF electrolytic cap from the other side, installed a 2 µF cap (which, judging from the lack of polarity indicators, may be a film cap) from the Squidwrench junk heap parts bin in its place, and hitched up the DSO150 because I brought it along:
Worked the first time and caught it in mid-blink! [grin]
The DSO150’s triggering remains a mystery, as it seems difficult to get a stable trace from a perfectly reasonable waveform. The scope didn’t trigger well on the astable’s original seconds-long pulses, perhaps due to a DC blocking cap in the triggering circuitry (whatever it may look like), but this waveform should be dead simple.
Having gained a visceral understanding of why MOSFET astables produce better battery life, this bipolar transistor design is just a milestone along the way.
The Smell of Molten Projects in the Morning 