This circuit of a 1964 Electronic Design uses a photodiode from the time. Modern equivalent can be used. The standby current is 1.2 mA.
This sophisticated RPM counter circuit with discrete integrated circuits was obtained in a 1993...
We found this circuit in an old American documentation. The operational amplifier is not common...
This oscillator can be found in other articles on the site. This is from a 4 MHz documentation, remembering...