This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
This circuit with the ICL8068 was taken from an article in the February 1981 Radio Electronics magazine....
The National Semiconductor operational amplifier, now owned by the Texas Instruments group, is no...
The Motorola MOC501O optocoupler has a complete amplifier inside the sensor, enabling the...