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 long-time circuit uses a field effect transistor, which may be the BF245, and depends on a...
The figure shows how to implement the AND function with a Norton LM3900 operational amplifier. The number of...
This circuit is from an old documentation, but it can be elaborated with ease, since the...