The purpose of this circuit is to cut off the high voltage when the bias voltage fails. The circuit is from a 1975 documentation and can be adapted for other purposes.
This circuit activates an old conventional cassette recorder when the telephone line is answered and...
In the figure we have two possible configurations for multivibrators with relay. The idea comes...
The LED is optically coupled to the LDR1 sensor to provide negative feedback to the circuit and...