Sound Operated Switchs

Description: This sensitive sound-operated switch can be used with a dynamic microphone insert or with an electret (ECM) microphone. If an ECM is used, then R1 (shown dotted) will need to be included, with a suitable value between 2.2k and 10k ohms. The two BC109C transistors form an audio preamplifier, the gain of which is controlled by a 10k potentiometer. The output is further amplified by a BC182B transistor. To prevent instability, the preamplifier is decoupled with a 100µF capacitor and a 1k resistor. The audio voltage at the collector of the BC182B is rectified by two 1N4148 diodes and a 4.7µF capacitor. This DC voltage will...

This circuit is designed as a sensitive sound-activated switch, suitable for various audio applications. The core of the circuit consists of two BC109C transistors configured as a preamplifier. The gain of this preamplifier is adjustable via a 10k potentiometer, allowing for fine-tuning based on the sensitivity required for the microphone being used. The circuit can accommodate both dynamic microphones and electret condenser microphones (ECMs). When using an ECM, it is essential to incorporate a resistor (R1) with a value ranging from 2.2k to 10k ohms to ensure proper operation.

The output of the preamplifier feeds into a BC182B transistor, which serves as a further amplification stage. This transistor enhances the audio signal before it is processed further. The design includes a decoupling network composed of a 100µF capacitor and a 1k resistor, which stabilizes the preamplifier and prevents oscillations that could lead to unwanted noise or instability in the circuit.

The audio signal at the collector of the BC182B is then rectified using two 1N4148 diodes, which convert the AC signal into a DC voltage. This rectified voltage is smoothed by a 4.7µF capacitor, ensuring a stable DC output that can be used to trigger other components in the circuit, such as relays or other switching devices. This design is particularly useful in applications where sound detection is required to activate or deactivate electronic devices, providing a reliable solution for sound-operated control systems.This sensitive sound operated switch can be used with a dynamic microphone insert as above, or be used with an electret (ECM) microphone. If an ECM is used then R1 (shown dotted) will need to be included. A suitable value would be between 2. 2k and 10kohms. The two BC109C transitors form an audio preamp, the gain of which is controlled by the 10k p reset. The output is further amplified by a BC182B transistor. To prevent instability the preamp is decoupled with a 100u capacitor and 1k resistor. The audio voltage at the collector of the BC182B is rectified by the two 1N4148 diodes and 4. 7u capacitor. This dc voltage will