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Simple Clap Switch Circuit using Speaker as MIC

With a single clap we can create a special circuit in this article that turns an object from ON to OFF!

It uses a standard speaker as a microphone to pick up claps and use that information to turn a switch ON or OFF.

Hand sounds alone are used to control lights or toys which is an interesting and fun project.

Circuit Working:

Parts List:

CategoryDescriptionQuantity
Resistors
1M1
10M1
330k2
10k2
100k3
Potentiometer 2k1
Capacitors
Ceramic 0.01μF2
Ceramic 0.47μF2
Semiconductors
Transistor BC5471
Transistor BC5572
MOSFET BS1701
Diode 1N41481
Relay 12V1
Speaker 8Ω used as MIC1

This circuit uses an innovative single coil latching relay as an essential component to create a simple clap switch design with increased sensitivity.

Although there are other ways to perform the latching function using a latching relay lowers the circuit and makes it easier to operate a relay contact interface for a 115 or 230V AC load, such a lightbulb.

Because the circuit has an excellent battery life the load only consumes 400uA and there is no relay coil current in either the On or Off states.

A computer speaker that also functions as a microphone records the clap signal which is then boosted by a high voltage gain audio amplifier before being picked up by a simple yet sensitive transistorized floating level detector.

In a later post the high voltage gain amplifiers specifications will be discussed.

Since no previous design of this kind has been published the circuits new floating level detector component could be innovative.

The unique nature of every component makes simulation simple.

An amplifier with a high voltage gain:

Since the computer speakers output is only about 200 uV a significant voltage boost is required.

The amplifier is composed of Q1 and Q2 and its output is situated at Q2s emitter.

About 400 uA of current is passing through R5 which is the circuits single DC load.

The voltage gain is around 1000 which is more than enough to operate the detector.

The speaker can detect relay operation noises thus it is necessary to set the sensitivity by adjusting pot P1 to prevent oscillation.

Separating the relay from the speaker could be a good way to deal with issue.

How a Battery Works:

Battery operation should only be used for testing for any actual use a wall wart power source is advised.

Additionally a 12V power supply seems to work well.

Detector of Floating Noise:

With just one PNP transistor and a few active parts the noise detector is unique and does not require any modifications.

An R-C circuit that monitors the DC voltage from Q2 separates the emitter of Q3 from the amplifier output.

R7 and R8 pre-bias the base of Q3 for increased sensitivity while C4 acts as a bypass capacitor to keep the voltage steady.

For lower sensitivity R8 can be left out.

Driver for Relays:

The low power noise detector can readily drive the BS170 MOSFET transistor used in the relay driver Q4 which has an extremely high input resistance.

In around 80 mS R9 successfully discharges C3 to the Vgs threshold of Q4 2V.

Formula:

When a loud sound like clapping is detected a clap switch circuit uses a speaker as a microphone (MIC) to turn on a switch or other electrical device.

The primary formulas usually involved are as follows along with the related functioning values:

Improving the MIC Signal:

Use the operational amplifiers gain formula for calculating the amplification factor (Av).

For an inverting amplifier setup check the below formula:

𝐴𝑣 = −𝑅𝑓 / 𝑅i𝑛

where,

The Threshold Selection Process:

Calculate the comparator circuits threshold voltage (Vth) to meet the necessary clap circuit sound level.

As necessary adjust the reference voltage input or resistor divider network.

Following these guideline one can create a functional clap switch circuit with a speaker acting as a microphone.

Depending on particular needs and component availability the circuit design might require to be modified.

For best results resistor levels and component types are easily adjusted to fine tune the sensitivity and sound boosting.

How to Build:

To build a Simple Clap Switch Circuit using Speaker as MIC following are the steps for connections and assembling:

Connect the Latching Relay for the Single Coil:

Connect the speaker on a computer:

Create the High Voltage Gain Audio Amplifier:

Put the Floating Level Detector into Practice:

Build the Relay Driver:

Connection to the Power Supply:

Examine and adjust:

Adapting:

Take note:

Conclusion:

Using a speaker as a microphone is a simple electrical circuit that transforms a speaker into a sound sensor.

Usually the circuit uses a switching mechanism to operate an external device and enhances the speakers weak output when it detects unexpected sounds such as claps.

This design enables hands free operation and it can be adjusted for a number of uses including alarm activation and lighting control.

For best results the circuits sensitivity and noise filtering are essential factors.

References:

Clap Switch

Design of a Clap Activated Switch

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