This circuit was found in a Popular Electronics of the 1990s. The sensor is a rotating mechanical system with a propeller-driven magnet to count pulses with a reedswitch.
We found this 3-transistor receiver in the July 1970 issue of Radio Electronics. The transistors may be...
This circuit was found in a 2001 documentation. It is a test of zener diodes that uses a voltmeter or...
This is the receiver from the previous alarm system. The circuit is from Radio Electronics, April...