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 circuit is a variation of the previous one, containing a modulation input. The components are the same....
This simple power supply is regulated by two zener diodes which, for a current of up to 200 mA,...
We found this circuit in a 1966 General Electric SCR manual. The circuit can be implemented with...