Here is a very interesting project of a sound to light LED circuit that can be built easily by using only few general components. The circuit will flash four LEDs at sound detected by the electret microphone and can be used for many purposes for example it will blink the LEDs on music. You can also add 5 to 10
more LEDs of 25mA in the circuit with their current limiting resistors.

The circuit is divided into three stages, first stage is an audio preamplifier built around transistor Q1, second stage is an audio amplifier built with transistor Q2 and the third stage is built using transistor Q3 which is working as a switch.

The electret microphone detects the audio signals and changes them in to electrical signal, these signals are amplified by the transistor Q1 and then further amplified by the transistor Q2. The amplified signal at the collector of the transistor Q2 goes in the base of the Q3 through the 270 ohms resistor making it switch ON and activate the LEDs. The sensitivity of the circuit can be adjusted with 20K variable resistor.

You can operate the circuit from 4.5 volt to 12 volt DC. But it is important to use the current limiting resistor for LEDs according to the operating voltage for example if you are using 4.5 volts to operate the circuit then use 100 Ohms current limiting resistor, on 6 volt use 220 ohms resistor.

You can also use 2N3904 transistors in the place of 2N4401 if you cannot find them. 


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