Build Your Own 3V Hearing Aid Circuit Diagram

Description

This affordable, general-purpose electronic hearing aid operates on 3V DC (two 1.5V batteries). The circuit can be easily constructed on a veroboard. For simplified assembly and maintenance, an 8-pin DIP IC socket for the TDA2822M is recommended.

TDA2822M

The TDA2822M is a widely utilized integrated circuit, specifically engineered for portable, low-power audio applications. This IC typically features a low quiescent current drain, making it suitable for battery-powered devices. It’s commonly found in applications requiring small form factors and efficient operation. Its availability in an 8-pin mini DIP package contributes to ease of integration.

Circuit Diagram:

Parts:

Circuit Operation:

Within this circuit, transistor Q1 and its associated components constitute the audio signal preamplifier for acoustic signals received by the condenser microphone and transformed into corresponding electrical signals. Resistor R5 and capacitor C3 demultiplex the power supply of the preamplifier stage, ensuring stable operation. Resistor R1 biases the internal circuitry of the low-voltage condenser microphone appropriately. The audio output from the preamplifier stage is fed into the input of the medium-power amplifier circuit through capacitor C2 and the volume control P1.

The medium-power amplifier section is constructed around the TDA2822M integrated circuit (not TDA2822). This IC, designed for small-scale, low-power audio amplification, is readily available in an 8-pin mini DIP package. The IC is wired in a bridge configuration to drive the 32-ohm monophonic earphone. Red LED (D1) serves as an indicator of power status. Resistor R8 limits the current drawn by D1. The output of this circuit provides an audio signal of 10 to 15mW, while the quiescent current drain remains below 1 mA.