Simple Clap Switch Circuit using Speaker as MIC

This post shows you how to build a special circuit that turns things on or off with a clap!

It uses a regular speaker as a microphone to pick up the sound of a clap, and then turns a switch on or off based on that sound.

This can be a fun way to control things like lights or toys with just the sound of your hands.

Circuit Working:

Parts List:

This circuit features a simple clap switch design with enhanced sensitivity utilizing a distinctive single coil latching relay as a key component.

While there are various methods for achieving the latching function the inclusion of the latching relay streamlines the circuit and facilitates a relay contact interface for operating a 115 or 230V AC load, such as a light bulb.

The circuit boasts efficient battery life since the load only draws 400uA, with no relay coil current in either the On or Off states.

The ‘clap’ signal is captured through a computer speaker functioning as a microphone amplified by a high voltage gain audio amplifier and identified through a simple yet sensitive transistorized floating level detector.

The details of the high voltage gain amplifier will be covered in a subsequent article.

The unique floating level detector section of the circuit might be groundbreaking as no similar design has been published before.

All components are discrete, allowing for easy simulation.

High Voltage Gain Amplifier:

Given that the computer speakers output is approximately 200uV a substantial voltage gain is necessary.

Q1 and Q2 constitute the amplifier with its output located at the emitter of Q2.

The circuits only DC load is the current flowing through R5 around 400uA.

The voltage gain is roughly 1000 more than sufficient for detector operation.

The sensitivity adjust pot P1 must be calibrated to avoid oscillation as the speaker can pick up relay operation sounds.

To address this separating the relay from the speaker might be desirable.

Battery Operation:

Battery operation is primarily for experimentation and any practical application is recommended to use a wall wart power supply.

A 12V power source should also be suitable.

Floating Noise Detector:

The noise detector is innovative, comprising a single PNP transistor and a few passive components, requiring no adjustments.

The emitter of Q3 is isolated from the amplifier output through an R-C circuit that tracks the DC voltage from Q2.

C4 functions as a bypass capacitor to maintain a stable voltage, while R7 and R8 pre bias the base of Q3 for improved sensitivity.

R8 may be omitted for reduced sensitivity.

Relay Driver:

The relay driver Q4 employs a BS170 MOSFET transistor with an exceptionally high input resistance easily driven by the low power noise detector.

R9 effectively discharges C3 to the Vgs threshold of Q4 2V in approximately 80mS.

Formula:

A speaker is used as a microphone MIC in a clap switch circuit, which senses clapping sounds or other loud noises to activate a switch or other electrical device.

The following are the fundamental formulas that are usually involved, along with the matching operating principles:

Enhancement of the MIC Signal:

To find the amplification factor (A_v) use the operational amplifiers gain formula.

For a setup using an inverting amplifier:

𝐴_𝑣 = −𝑅_𝑓 / 𝑅_i𝑛

where,

• R_f is the feedback resistor and R_in is the input resistor.

Finding the Threshold:

For the comparator circuit, find the threshold voltage (V_th) that corresponds to the desired sound level (clap).

As necessary, make adjustments to the reference voltage input or resistor divider network.

You may build a working clap switch circuit with a speaker acting as a microphone by according to these guidelines and perhaps modifying the circuit design in light of particular needs and component availability.

For best results, resistor values and component types may be adjusted to fine tune sensitivity and noise immunity.

How to Build:

Building the clap switch circuit with a high sensitivity design involves assembling the specified components and connecting them as described in the original content.

Connect the Single Coil Latching Relay:

• Identify the relays coil connections typically labeled as coil+ and coil-.
• Connect the coil+ to a positive voltage source and coil to the circuit ground.

Integrate the Computer Speaker:

• Utilize the computer speaker as a microphone by connecting its output to the input of the high voltage gain audio amplifier Q1, Q2.

Build the High Voltage Gain Audio Amplifier:

• Connect the components Q1, Q2, R5 and P1 as specified in the original content.
• Ensure proper power supply connections for the amplifier.

Implement the Floating Level Detector:

• Assemble the components Q3, R7, R8, C3 and C4 according to the provided information.
• Make sure to connect the output of the high voltage gain amplifier to the input of the floating level detector.

Create the Relay Driver:

• Build the relay driver using Q4, BS170 MOSFET and R9 as outlined in the original content.
• Connect the output of the floating level detector to the input of the relay driver.

Power Supply Connection:

• Depending on your preference, use either a battery or a wall wart power supply.
• Connect the positive terminal of the power supply to the circuits positive terminal and the negative terminal to the circuit ground.

Test and Calibrate:

• Power up the circuit and test its functionality.
• Adjust the sensitivity pot P1 to prevent oscillation and optimize performance.
• Test the clap switch by clapping near the computer speaker to observe the relay activation.

Fine-Tuning:

• Fine tune the circuit as needed making adjustments to component values or layout for better performance.

Note:

Remember to handle electronic components with care double check connections and ensure that the power supply voltage matches the requirements of the components.

If you are not experienced with electronics, consider seeking assistance from someone with more expertise or consulting additional resources for a safer and more successful build.

Conclusion:

In conclusion, a Clap Switch Circuit using a speaker as a microphone is a simple electronic setup that converts a speaker into a sound sensor.

The circuit typically involves amplifying the weak signal from the speaker detecting sharp sounds like claps, and using a switching mechanism to control an external device.

This design allows for hands free operation and can be customized for various applications such as lighting control or alarm activation.

The sensitivity of the circuit and noise filtering considerations are crucial for optimal performance.

References:

Clap Switch

Design of a Clap Activated Switch