Optical sensor for PC (CB20548E)

This circuit was found in a PC documentation from 1996. It can be used as a shield with modern microcontrollers.

Unusual TTL Oscillator (CB24721E)
This circuit is for transducers (headphones or speakers) of 200 to 300 ohms. The frequency is...
TV Stereo Simulator (CB16591E)
This circuit is from 1987 when there were only analog TVs and stereo sound was still a novelty for this...
Astable Timer 555 (CB9369E)
This circuit was obtained in a Hands-On Electronics from the 90's. The circuit turns on one LED at...