Archive for October 14th, 2014

Astable Multivibrator: Round 2

Another pass at the old Squidwrench soldering project, in light of some upcoming events, seemed in order:

Astable Multivibrator - as-built - simulation

Astable Multivibrator – as-built – simulation

The 10 µF caps scale the output to visible blinkiness. Their polarity may seem backwards, but the red trace in the simulation shows that the net voltage is positive in that direction for nearly the entire cycle. They see only two forward biased junctions in the other direction, so they shouldn’t blow up.

I built it with resistors from the SqWr junk box parts cabinet that were close to the nominal values.

Connecting the transistor base / cap charging resistors to the power supply, rather than the LEDs, gets rid of the tiny current when the LEDs should be off.

The cap-and-pulse-generator dingus on the bottom kickstarts the simulation; it doesn’t have any physical significance.

Memo to Self: Build one with a pair of ET227 transistors and some 100 W tungsten bulbs…