This article explains how to construct a special circuit that is used to switch the objects ON or OFF with a simple sound of clap!
It detects the sound of a clap using a standard speaker as a microphone and then it uses that sound to turn a switch ON or OFF.
This is a fun method to use the sound of the hands to control object like toys or lights.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistors | ||
| 1M | 1 | |
| 10M | 1 | |
| 330k | 2 | |
| 10k | 2 | |
| 100k | 3 | |
| Potentiometer 2k | 1 | |
| Capacitors | ||
| Ceramic 0.01μF | 2 | |
| Ceramic 0.47μF | 2 | |
| Semiconductors | ||
| Transistor BC547 | 1 | |
| Transistor BC557 | 2 | |
| MOSFET BS170 | 1 | |
| Diode 1N4148 | 1 | |
| Relay 12V | 1 | |
| Speaker 8Ω used as MIC | 1 |
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,
- Rf is the feedback resistor
- Rin is the input resistor.
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:
- Find the coil connections on the relays which are usually marked coil+ and coil-.
- Connect the coil to the circuit ground and the coil+ to a source of positive voltage.
Connect the Computer Speaker:
- Connect the output of the computer speaker to the input of the high voltage gain audio amplifiers Q1 and Q2 to use it as a microphone.
Construct the Audio Amplifier with High Voltage Gain:
- The original text specifies how to connect Q1, Q2, R5 and P1.
- Check that the amplifiers power supply connections are correct.
Put the Floating Level Detector into Practice:
- Using the given information assemble the parts Q3, R7, R8, C3, and C4.
- Ensure that the input of the floating level detector is connected to the output of the high voltage gain amplifier.
Build the Relay Driver:
- As described in the earlier text construct the relay driver using Q4, BS170 MOSFET and R9.
- Connect the floating level detectors output to the relay drivers input.
Connection to the Power Supply:
- Use a wall wart power supply or a battery depending on the preferences.
- Connect the power supplies negative terminal to the circuit ground and its positive terminal to the circuits positive terminal.
Examine and adjust:
- Turn the circuit ON and check that it is working well.
- For the best results and to avoid oscillation adjust the sensitivity pot P1.
- To test the clap switch clap close to the computer speaker and watch as the relay activates.
Adjusting:
- Adjust the circuits configuration or component values as necessary to improve performance.
Note:
One should remember to handle electrical components with care, double check connections and ensure that the power supply voltage is right for the components requirements.
If somebody is unfamiliar with electronics consider using alternative resources or seeking assistance from a more experienced person for a safer and more efficient construction.
Conclusion:
Using a speaker as a microphone is a simple electrical circuit 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.