The expansion rate of this circuit is determined by R. The circuit can use any operational amplifier and the power supply must be symmetrical. Resistor R must be less than 10k.
With the configuration shown in the figure, we have the relay being activated when the microphone picks...
This TTL generator that can function as a control shield or external clock for microcontrollers was found in...
The OP07 operational amplifier is not common today, as the circuit is from an old European manual....