Build a Low-Power IR Audio Amplifier Circuit Diagram

Description

This cost-effective project enables the reproduction of audio from a television without generating any disturbance for surrounding individuals. It avoids the use of any direct wiring connection between the television and the loudspeaker. Instead, it utilizes invisible infrared light to transmit audio signals from the television to the loudspeakers. A range of up to 6 meters is achievable without a lens, and this range can be extended further by incorporating lenses and reflectors along with infrared sensors, which comprise both transmitters and receivers.

An audio output transformer (T1) is employed (in reverse) to couple the audio output from the television to the infrared transmitter. Two transistors, Q1 and Q2, are used to amplify the audio signals received from the television through the audio transformer. The output windings, characterized by a lower gauge or thicker wiring, are utilized for connections to the television side, while the high-impedance windings are connected to the infrared transmitter. This infrared transmitter can be powered via a 9-volt mains adapter or a 9-volt battery. A red light-emitting diode (D1) within the transmitter circuit functions as a Zener diode (0.65V) alongside a supply-on indicator. 

Transmitter's operation:

The infrared transmitter utilizes a two-stage transistor amplifier to drive two series-connected infrared light-emitting diodes (D2). The amplifier is designed to efficiently deliver the amplified audio signal to the infrared LEDs. An audio output transformer (T1) is coupled to the audio output from the television to the infrared transmitter. Transistors Q1 and Q2 provide amplification of the audio signals received from the television through the audio transformer. Low-impedance output windings (constructed with a lower gauge or thicker wiring) are used for connections to the television side, while high-impedance windings are connected to the infrared transmitter. This infrared transmitter can be powered from a 9-volt mains adapter or a 9-volt battery. 

Transmitter diagram:

Receiver's operation:

The infrared receiver incorporates a widely utilized operational amplifier (IC1), designated as µA741, along with an audio-frequency amplifier integrated circuit (IC2), designated as LM386, alongside a phototransistor (Q3) and several discrete components. The sound originating from the television is transmitted through infrared light-emitting diodes, received by the phototransistor Q3, and subsequently fed into pin 2 of the operational amplifier IC1 (IC1). The gain of the amplifier can be adjusted using a potentiometer (P2). The output of the operational amplifier IC1 is fed to the LM386 (IC2) via a capacitor (C7) and a potentiometer (P3). The reproduced sound is heard through the receiver’s loudspeaker. A potentiometer (P3) is employed to control the volume of the loudspeaker SPKR (8-ohm, 1W). 

Receiver diagram:

Parts: