Audio Controlled Mains Switch Circuit

This circuit will disconnect the line supply to audio or video equipment if there has been no input signal for approximately 2 seconds. Switch SI provides manual operation, while switch S2 functions as a reset mechanism. This circuit allows time for changing a tape or compact disc. Additionally, around 50 mV of audio signal is required for operation.

The described circuit serves as an automatic power management solution for audio and video equipment, enhancing energy efficiency and user convenience. The primary function is to monitor the presence of an audio or video signal, and if the signal falls below a threshold (approximately 50 mV), the circuit will interrupt the power supply after a delay of about 2 seconds. This feature is particularly useful in scenarios where equipment is idle, preventing unnecessary power consumption.

The circuit includes two key switches: SI and S2. Switch SI is designed for manual operation, allowing users to override the automatic shut-off feature when needed. For instance, if a user is aware that they will be changing a tape or compact disc, they can manually keep the circuit engaged. Switch S2 serves as a reset mechanism, enabling the user to restore power to the equipment after it has been turned off due to inactivity.

The design likely incorporates a timing circuit, such as a capacitor-resistor (RC) network, to establish the 2-second delay. When the audio signal is present, the voltage across the capacitor remains above the threshold, keeping the circuit active. Once the signal drops below the required 50 mV, the capacitor begins to discharge, and if it drops below a certain level within the 2-second window, a relay or transistor may be triggered to cut off the power supply.

This circuit can be implemented using standard electronic components such as resistors, capacitors, transistors, and relays. The selection of components should ensure that the circuit operates reliably within the specified voltage and current ratings of the audio or video equipment it is designed to protect. Overall, this circuit design exemplifies a practical approach to reducing energy waste in consumer electronics while providing essential user controls for manual operation and reset functionality. This circuit will switch off the line supply to audio or video equipment if there has been no input signal for about 2 seconds. SI provides manual operation and S2 acts as a reset. This circuit allows for time to change a tape or compact disc. About 50 mV of audio signal is necessary.