This code key uses a PLL and an oscillator that generates two frequencies that must be recognized for the relay to be activated. The circuit is from an 80's Popular Electronics.
High voltage electrolytic capacitors can be recovered by applying high voltage to their terminals. This...
Using common components, this circuit found in a 2003 publication, controls the level of a water...
We found this circuit in a 90's European schematic. The circuit can be implemented with almost any...