Introduction

The Simple and Cheap Clap Switch Circuit is a practical and fun DIY electronics project that allows you to control appliances or lights with the sound of a hand clap. Using just a few basic components like a microphone, transistor, and relay, this circuit is easy to assemble and ideal for beginners exploring sound-activated control systems. It’s an affordable way to understand the fundamentals of audio signal detection and switching, making it perfect for school projects or hobbyist experiments. With this simple and cheap clap switch circuit, you can add a touch of automation to your home without spending much.

For Full Project:

https://electronicsworkshops.com/2025/03/26/simple-and-cheap-clap-switch-circuit/

Working Principle

The clap switch operates by detecting the sound of a clap and using it to toggle a relay, which can control an external device (like a light or fan). Here’s how it works step-by-step:

Sound Detection:

A condenser microphone (MIC) picks up the sound waves produced by a clap. This sound is converted into a small analog voltage signal.

Signal Conditioning:

The signal is passed through a biasing and filtering stage (using resistors R2, R3 and capacitor C2) to clean up and amplify the signal to a usable level.

Microcontroller Processing:

The filtered signal is fed into the ATtiny85 microcontroller (U2) at a digital input pin. The microcontroller is programmed to detect a spike or pulse that matches the characteristics of a clap.

Output Trigger:

Upon detecting a valid clap signal, the microcontroller sends a high output signal (TRIGGER) to activate transistor Q1 (2N3904).

Relay Activation:

The transistor switches on and allows current to flow to the relay coil (RLY1). This energizes the relay, closing or opening its contacts to control an external AC load.

Protection and Indication:

Diode D1 (1N4007) protects the transistor from back EMF when the relay coil is turned off.

LED1 indicates power is supplied to the system.

Schematic Diagram

This circuit is a clap switch system that uses an ATtiny85 microcontroller to detect sound and control a relay. A condenser microphone (MIC1) captures the sound (such as a clap), which is then filtered and amplified by resistors (R2, R3) and capacitor (C2), producing a clean analog signal at the SOUND_INPUT pin. This input is fed into the ATtiny85 (U2), which processes the signal and, upon detecting a valid sound pattern, sends a high signal on its output pin labeled TRIGGER. This output drives an NPN transistor (Q1, 2N3904), allowing current to flow through and energize a 5V relay (RLY1). The relay can then switch an external AC load. A flyback diode (D1) protects the transistor from voltage spikes. Additionally, an LED (LED1) with resistor (R4) acts as a power indicator, and the whole system is powered by a HLK-PM01 module converting AC to 5V DC.

Schematic Diagram Clap Switch

PCB Files

Project Files

Conclusion

The simple and cheap clap switch circuit offers an easy and affordable solution for controlling electronic appliances using sound (clap) as a trigger. Utilizing basic components like a microphone, transistors, resistors, and a relay, the circuit detects a clap sound and activates or deactivates the connected load. This project is ideal for beginners to understand basic sound detection and switching principles, and it can be used in home automation or DIY electronic applications. Its low cost and simplicity make it an excellent entry-level project for learning electronics and sound-based control system.

For Full Project:

https://electronicsworkshops.com/2025/03/26/simple-and-cheap-clap-switch-circuit/