Circuit Lake

Electronic Project and Circuit Collection

Low Cost Hearing Aid, TDA2822M

05/28/2013 Category: Analog, Audio, Miscellaneous

This Low Cost Hearing Aid project is built based on TDA2822M IC. This general-purpose electronic hearing aid needs 3V DC (2×1.5V battery) to works. Use an 8-pin DIP IC socket for TDA2822M for easy assembling and maintenance.

DIY Electronics hearing AidSimple & Low cost hearing Aid Schematic

Part List:

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.