We found this circuit in a 1964 Electronic Design. It divides the frequency of a 20 MHz signal by 2. The circuit uses a transistor from that time. Details of the coils were not given.
This 80's circuit, suggested in Texas Insrtruments documentation, uses a Hall effect sensor. The...
This circuit is from the 80's component manual itself, but can be applied to more modern...
This humidity sensor indicates the different levels of conduction of the sensors through an LED...