A Low Cost Hearing Aid

Small and portable unit, Useful for old men and old women

This low-cost, general-purpose electronic hearing aid works off 3V
DC (2×1.5V battery). The circuit can be easily assembled on a veroboard.
For easy assembling and maintenance, use an 8-pin DIP IC socket for TDA2822M.

A Low Cost hearing Aid Schematic

A Low Cost hearing Aid Schematic

Parts:

P1 = 10K
R1 = 2.2K
R2 = 330K
R3 = 680R
R4 = 33R
R5 = 100R
R6 = 4.7R
R7 = 4.7R
R8 = 220R
C1 = 0.01uF-10V
C2 = 100nF-63V
C3 = 47uF-10V
C4 = 10uF-10V
C5 = 0.01uF-10V
C6 = 100uF-10V
C7 = 100nF-63V
C8 = 100nF-63V
D1 = Red LED
Q1 = BC547
IC1 = TDA2822M
EP1 = Mono Earphone 32R
SW1 = On-Off Switch

Circuit Operation:

In this circuit, transistor Q1 and associated components form the
audio signal preamplifier for the acoustic signals picked up by the
condenser microphone and converted into corresponding electrical
signals. Resistor R5 and capacitor C3 decouple the power supply of the
preamplifier stage. Resistor R1 biases the internal circuit of the
low-voltage condenser microphone for proper working. The audio output
from the preamplifier stage is fed to the input of the medium-power
amplifier circuit via capacitor C2 and volume control P1.

The medium-power amplifier section is wired around popular audio
amplifier IC TDA2822M (not TDA2822). This IC, specially designed for
portable low-power applications, is readily available in 8-pin mini DIP package. Here the IC is wired in bridge configuration to drive the 32-ohm general-purpose monophonic earphone. Red LED
(D1) indicates the power status. Resistor R8 limits the operating
current of D1. The audio output of this circuit is 10 to 15mW and the
quiescent current drain is below 1 mA.

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