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.
This didactic circuit was found in a 2001 documentation. It presents the result of programming in binary...
This VFO circuit generates signals from 2 Hz to 50 Hz. We found it in Popular Electronics from...
This circuit can be used as a buzzer from 3 different locations, allowing you to identify where it went...