Found in European documentation from the 1980s, this circuit was originally designed for computer applications of the time. However, the basic idea can be adapted for use with microcontrollers.
This circuit monitors the voltage of a 12 V battery. The indicated levels let you know if the...
This circuit turns on an old cassette recorder when the telephone rings, thus enabling the...
This circuit is from an old Popular Electronics, but it can be easily implemented nowadays, even...