Audio Controlled LED Circuit using Transistors

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In this project, we will make Audio Controlled LED Circuit using a transistor. In an audio-controlled LED circuit, LEDs turn on and off according to the music. This circuit is simple and efficient, it requires a small amount of audio signal at the input, which comes from the output of the headphone socket of any audio-playing device such as an mp3 player, CD player, computer, cellphone, etc.

We will make this circuit using 15 LEDs and a transistor. This circuit is based on a BD140 transistor, it’s very simple and basic and needs only a few components. LEDs turn on and off according to the pitch and length of the sound or rhythm, this circuit design allows it to pick high-intensity sound like a bass. These LEDs follow the high pitch of sound and beats and turn off and on accordingly.

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Hardware Components

The following components are required to make Audio Controlled LED Circuit

S.no	Components	Value	Qty
1.	Audio input	–	1
2.	Resistor	100K, 75Ω	1, 5
3.	Electrolytic Capacitor	10µF	1
4.	Diode	1N4148	2
5.	PNP Transistor	BD140	1
6.	LED	–	15
7.	Battery	12V	1
8.	Breadboard	–	1
9.	Connecting Wires	–	1

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For a detailed description of pinout, dimension features, and specifications download the datasheet of BD140

Audio Controlled LED Circuit

Working Explanation

The operating voltage of this circuit is 12V DC. We are using 15 LEDs in this circuit and a group of three LEDs is connected with a single current limiting resistor. The transistor that we are using is BD140 and you can connect up to 60 LEDs with it.

The audio input picks up the sound signals and converts them into voltage levels which are further fed into an R-C filter to eliminate the noise from the sound. The PNP transistor is used to amplify the audio signals coming from the filter and they are given to the array of resistors and LEDs. The transistor helps in amplification and glows the LEDs according to the sound pattern.

You can increase the number of LEDs if you want but make sure to connect them in the same manner as they are connected in this circuit diagram. For further increasing the LEDs you can change the transistor as well, like MJ2955 or TIP32 transistor