Audio activated delay switch is a circuit that can activate a relay switch for a specific time period. For example, when we are listening to an FM radio station there’s a sudden increase in volume when any advertisement or song plays. But with the help of this circuit that sudden increment of volume can be muted for 15 seconds and if the volume is still high this circuit will mute it for another 15 seconds. Today we are going to build an Audio Activated Delay Switch Using Transistors.
This circuit is easy to construct, we are only using transistors, relay, and a few other discrete components. This project is very useful for audio-related purposes.
Hardware Components
The following components are required to make Audio Activated Switch Circuit
| S.no | Components | Value | Qty |
|---|---|---|---|
| 1. | Transistor | 2N3906, 2N3904 | 1, 1 |
| 2. | Audio input | – | 1 |
| 3. | Resistor | 1K Var, 2.2K, 470K, 47K | 1, 1, 1, 1 |
| 4. | SPDT Relay | 12V | 1 |
| 5. | Diode | 1N4148 | 1 |
| 6. | Electrolytic Capacitor | 10µF, 100µF | 1, 1 |
| 7. | Diode | 1N4007 | 1 |
| 8. | Battery | 12V | 1 |
2N3904 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3904
2N3906 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of 2N3906
Audio Activated Switch Circuit
Construction
Remember the following things while constructing this circuit,
- Connect the Audio In points with the internal wires connected with the female jack by opening the back cover of your radio.
- Do not connect it with the outside of the female headphone jack through a male headphone jack because it will always disconnect the speaker
- This circuit is powered by a 12V battery, it can also be operated with low voltage like 5-6V, but you will have to use the relay of the same voltage.
Working Explanation
After getting finished with construction and all the connections let’s see how this circuit works.
Turn your radio on and start increasing the volume, stop at the point where you want the radio to mute. Now with the help of the variable resistor adjust the resistance until the relay activates then connect the relay outputs between one speaker wire, by doing this whenever the volume will reach the above-specified level relay will activate and it disconnects the speaker. The ON time of the relay depends on the value of the capacitor used, you can increase the value of the 100µF capacitor to increase the ON time of the relay.
Applications and Uses
- Automatic audio recording
- Audio activated relay switch
- Automatic muting of any audio equipment
