Sensitive Sound Activated LED with 2n4401 Transistors

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A very sensitive sound-activated LED circuit activates LEDs by even detecting distant sounds. This circuit here converts sound energy from the environment even with low tune to electrical energy. The circuit includes a combination of transistors, diodes, resistors, capacitors, LEDs, and an Electret microphone.

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Hardware Components

The following components are required to make Sound Activated LED Circuit

S.no	Component	Value	Qty
1.	Transistor	2N4401	3
2.	Diode	1N4148	2
3.	LED	–	9
4.	Battery	9V to 12V	1
5.	Variable resistor	100KΩ	1
6.	Resistor	68Ω, 1.2KΩ, 10KΩ , 220KΩ, 620KΩ	3, 1, 2, 1, 1
7.	Ceramic Capacitor	0.1nF, 100nF	1
8.	Electrolytic capacitor	100nF, 1µF	1
9.	Electret Mic	–	1

2n4401 Pinout

For a detailed description of pinout, dimension features, and specifications download the datasheet of 2n4401

Sound Activated LED Circuit

Working Explanation

The electret microphone in the circuit catches sound signals and converts them into electrical signals. The electrical signal is passed to the pre-amplification phase done by transistor Q1. Furthermore, transistor Q2 amplifies the signal and sends it to diodes D1 and D2. The signal passes through the capacitor 10µF to perform filtration and then to the diodes. Both the diodes rectify the electrical signal. Thus, the DC signal then achieved goes to the base of transistor Q3 to activate it. LED lights up as soon as transistor Q3 activates.

Adjustment of sensitivity of the circuit is done by 100KΩ variable resistors. The operating voltage of the circuit is 12V but 9V is also a possibility. For this case, one LED from each of the parallel connections, as shown above, must be removed. Also, the 68Ω resistor is to be replaced with 180Ω. Furthermore, the circuit can include 3-6 more LEDs of 25mA. Moreover, the addition of BD135 can include up to 40 LEDs of 25mA in the circuit.