Clap Switch Circuit using Speaker as MIC

In this article with one clap we can make a Clap Switch Circuit using Speaker as MIC.

It can turn something ON or OFF!

We use normal speaker like microphone which hear the clap sound and then turn switch ON or OFF.

Only hand sound controls light or toy.

This is fun and interesting project to try.

Circuit Working:

Parts List:

This circuit uses new idea for one coil latching relay.

It helps make easy clap switch with better sound catching.

Other ways also work but using latching relay make circuit small and simple.

It can turn ON/OFF with big things like 115V or 230V AC load like lightbulb.

Circuit uses very little battery and it uses only 400 microamp.

Relay coil uses no power when ON or OFF.

One computer speaker act like microphone and it catches clap sound.

Then sound goes to amplifier with big voltage boost and after that a small transistor detector catches the signal.

Later we will talk more about this amplifier.

This type of detector are not seen before maybe it is a new idea.

Every part in circuit is special that makes it easy for testing.

High Gain Amplifier:

Speaker give only small signal to about 200 microvolt so we need big boost.

Amplifier uses two parts: Q1 and Q2 and output come from Q2 emitter.

Only 400 microamp goes through R5 and that is the the only DC load.

Voltage gain is around 1000 which is good enough for detector.

Speaker can also hear relay clicking sound.

So we use P1 to set sensitivity if not set it may start looping.

Best to keep speaker and relay far from each other.

Battery Use:

Battery is okay for testing only and for regular use better to use wall power supply.

12V power supply also works good.

Noise Detector (Floating):

Only need of one PNP transistor and few parts it is very simple with no need to change anything.

One R-C circuit look at voltage from Q2 which keeps Q3 emitter separate from amplifier output.

R7 and R8 help base of Q3 feel signal better and C4 keeps voltage steady.

If we want less sensitivity then do not use R8.

Relay Driver:

Noise detector sends signal to Q4, that is BS170 MOSFET.

It needs very small input so it is easy to drive.

R9 take 80 milliseconds to drain C3 and send 2V to Q4 gate which is enough to turn relay ON/OFF

Formula:

When loud sound happens like clap this circuit hear it and turn ON switch or other electric thing.

It uses speaker like microphone (MIC).

Some main formulas help to make this work and here they are with simple explanation:

Making MIC Signal Strong:

To make MIC sound signal louder we must use amplifier.

For that use this formula to find gain (Av):

Av = -Rf / Rin

where:

• Rf is the feedback resistor
• Rin is the input resistor

This formula is for inverting amplifier setup.

Setting the Sound Level Threshold:

We need to tell circuit what sound level is a “clap” that is called threshold voltage (Vth).

Use comparator circuit to set Vth.

Change reference voltage or resistor values to adjust this level.

Follow these steps to build good clap switch.

The speaker works like microphone and catches hand clap sound.

Depending on parts we have or what we need maybe changes design a little.

For best work choose right resistor values and good quality parts.

How to Build:

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

How to Connect Latching Relay (Single Coil):

• Find where to connect relay coil it usually show as coil+ and coil-.
• Connect coil- to ground and connect coil+ to positive power supply.

Connect Computer Speaker as Microphone:

• Use computer speaker as MIC and take output wire from speaker and connect it to input of audio amplifier with transistors Q1 and Q2.

Make the High Voltage Gain Amplifier:

• Connect parts Q1, Q2, R5 and P1 same like in diagram.
• Check power connections of amplifier are correct.

Build Floating Level Detector:

• Now put together parts Q3, R7, R8, C3 and C4 as shown.
• Connect output of high gain amplifier to input of this detector.

Make Relay Driver:

• Use Q4 BS170 MOSFET and R9 to build relay driver.
• Connect output of level detector to input of relay driver.

Power Supply Connection:

• We can use battery or wall power which is up to us.
• Connect power negative (-) to circuit ground.
• Connect power positive (+) to circuits positive rail.

Check and Adjust Circuit:

• Turn ON power and see if circuit works.
• Turn P1 to set how sensitive circuit is.
• Clap near speaker and relay should turn ON or OFF.

Improve Circuit (If Needed):

• If we want better performance then change some part values or design.

Important Notes:

• Be careful with electric parts.
• Check wires and power before turning ON.
• Use right voltage for safety.
• If not sure then ask someone who knows electronics for help.

Conclusion:

This Clap Switch Circuit using Speaker as MIC.

It hears clap sound and turn ON/OFF devices.

Weak sound from speaker gets boosted and relay switch turns something ON like light or alarm.

It is good for hands free control and we can change circuit for many uses.

References:

Clap Switch

Design of a Clap Activated Switch