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 metronome configuration with the 555, quite common was found in a 90s Hands On Electronics. The...
We found this circuit in a 1964 Electronic Design. Transistors can be modern general-purpose...
As monostable we have a proximity switch that can be used as a shield, since the capacitance of...