Clap Swtich

Topics: Transistor, Switch, Electronics Pages: 5 (1004 words) Published: October 17, 2011

I would like to thank my supervisor Mr. Duminda Wijesinghe, my partner Miss. Menasha Tilekeratne, families of the group members and Auston Management for giving their fullest support and guidance to make this project a success. If it had not been for them this would not have been possible.

So I thank you from the bottom of my heart.


The aim of this project is to help disabled people who need constant care and protection due to their disability. This project helps them avoid accidents and inconveniences caused when handling electrical equipments.

This project helps them to operate switches on their ‘own’, for example turn on/off lights. The switch is controlled very simply. The switch turns ON at the sound of the first clap, and turns OFF at the second clap. The claps should be loud enough.

An electret microphone receives the sound of a clap, or a shout or any sound for example dropping of a box. It generates an electrical signal corresponding to the received sound. The successive transistor phase helps to amplify this signal. The system’s memory is constructed by two transistors that are cross coupled as a bistable multivibrator. One transistor would be turned ON while the other would be turned OFF, and each would continue to enforce the state of the other. The circuit will retain its state until it is disturbed by another sound. Thus, this circuit shows the simplest possible binary memory.

The system was virtually run by multisim software. This circuit can be useful to almost anybody and also protects them from electric shocks.

Table of Contents


2.0Solution Design
2.1Input Transducer
2.4Changing State


4.0Further Work


Appendix A



Electret Microphone

Bistable Multivibrator – Transistor
Has 2 states; ON / OFF
LEDs are either


Fig. 1.1

2.0System Design

The system has 5 main stages; they are input, amplifier, memory, changing state and output. Fig. 2.11

2.1Inputs Transducer

The electret microphone is a very sensitive device which is also called as a ‘condenser microphone’. There is a stretched electret film inside it which vibrates in coherence with any sound falling on it. These vibrations induce an electric charge on the close by perforated plate. The field effect transistor converts these into corresponding changes in current.

Fig. 2.2
A transistor stage amplifies the signal from the microphone.


A bistable multivibrator arrangement is constructed by two transistors that are cross coupled. This arrangement makes the circuit to remember. One of transistors is OFF while the other is ON. The circuit has two states and thus shows a simple binary memory. One state enforces the other. The current state of the circuit would not change unless disturbed by another external noise.

Fig. 2.3

2.4Changing State

The system changes the state, which is the LEDs turn ON and OFF so long as the switch of the circuit is closed. Below figure shows the diagram of a switch.

Fig. 2.4

A bunch of LEDs are used to produce a fair amount of light. Their brightness can be increased by reducing the amount of the series resistors connected to them to 220 ohms provided you keep within the ratings of the LEDs.

Fig. 2.5 Fig. 2.6

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