Sound follows us in every moment of our life.
Wherever we go sound travels with us.
Sometimes we need a small electronic circuit that can sense sound and give output.
A sound sensor is useful in many projects like clap switch, voice controlled light, sound activated alarm, toys and automation systems.
This article explains a Sound Sensor Circuit using IC LM393, microphone, transistor BC547, electret microphone, LED and with few resistors
Circuit Working:
Parts List:
| Component Type | Value | Quantity |
|---|---|---|
| Resistors | 10k 1/4 watt | 4 |
| 47k 1/4 watt | 1 | |
| 330Ω 1/4 watt | 1 | |
| Potentiometer 50k | 1 | |
| Capacitor | Ceramic 1nF | 1 |
| Semiconductors | IC Comparator LM393 | 1 |
| Transistor NPN BC547 | 1 | |
| Electret Microphone | 1 | |
| LED Red | 1 |
The circuit starts with a small condenser microphone.
It converts sound into small electrical signals.
These signals are very weak.
So they are passed through capacitor C1.
This capacitor blocks DC and passes only AC sound signal.
Then signal goes to transistor Q1 BC547.
Transistor works as amplifier.
Resistors R2, VR1 and R3 give biasing to transistor.
Amplified signal is then given to comparator IC LM393.
The comparator compares two voltages.
+Input pin 3 gets signal from transistor.
-Input pin 2 gets a reference voltage from divider R4 and R5.
If sound signal is higher than reference then comparator output goes low.
Because LM393 is open collector type then LED1 will glow through resistor R6 whenever sound is detected.
Formulas with Calculations:
Voltage divider at -input pin is with simple formula:
Vref = Vcc * (R5 / (R4 + R5))
where,
- Vcc is 5V
- R4 is 10k and
- R5 is 10k
Vref = 5 * (10k / (10k + 10k)) = 2.5V
So comparator will switch when amplified sound signal crosses 2.5V
Gain of transistor stage approx = Rc / Re
Here,
- Rc = R3 = 10k
- Re is internal emitter resistance around 25mV/Ie.
With small current gain amplification is enough to drive a comparator.
How to Build:
To build a Sound Sensor Circuit using IC LM393 following are the connections steps:
- Gather all parts same as in circuit diagram.
- Electret Microphone one pin goes to ground and other pin go to R1 and C1.
- R1 is 10k pull up resistor and it connects to Vcc.
- C1 is 1nF capacitor and it passes audio signal to base of Q1.
- Q1 is BC547 transistor its emitter go to ground, collector go to R3 and base go to VR1 and ground.
- R2 is 47k and it connect between Vcc and base for bias.
- R4 and R5 are both 10k and they make voltage divider and they go between Vcc and ground. Middle point go to pin 2 of IC1.
- Pin 3 of LM393 connect to collector of transistor.
- Pin 4 of LM393 go to ground and pin 8 go to Vcc.
- Pin 1 of LM393 is output and this output drive LED1 through R6 330 ohm.
Conclusion:
This Sound Sensor Circuit using IC LM393 is simple and with low cost.
It uses only few parts and run on 5V supply.
Microphone catch sound.
Transistor make signal big.
Comparator check signal with reference and LED glow when sound is there.
VR1 change sensitivity of sensor.
This circuit is used in clap switch, sound alarm, toys and small automation.