This simple circuit to monitor the frequency of the power grid uses an analog indicator. The adjustment trimpot can be 4k7 and the indicator is 100 mA full scale.
Found in a 1960s RCA manual, this circuit uses components from the era. For the indicated circuit R1 is...
This circuit is from a 1990 publication but can still be assembled today with some component...
This circuit aims to use the output of a microcontroller with low current to drive a load of a...