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This is a low-cost electronic hearing aid circuit diagram that works off
3V DC or 2x1.5V battery.

Parts List :
R1(Resistor) ------------------ 2.2 K
R2 -------------------------------- 330 K
R3 -------------------------------- 680 ohm
R4 -------------------------------- 33 ohm
R5 -------------------------------- 100 ohm
R6 -------------------------------- 4.7 ohm
R7 -------------------------------- 4.7 ohm
R8 -------------------------------- 220 ohm
C1(Capacitor) ---------------- 0.01 microF
C2 -------------------------------- 100 nF
C3 -------------------------------- 47 microF , 10V
C4 -------------------------------- 10 microF , 10V
C5 -------------------------------- 0.01 microF
C6 -------------------------------- 100 microF , 10V
C7 -------------------------------- 0.1 microF
C8 -------------------------------- 0.1 microF
T1 (Transistor) --------------- C1740 or BC547
IC --------------------------------- TDA 2822M
LED ------------------------------ Genarel red LED
Mic -------------------------------
Earphone ------------------------- 32 ohm

Circuit Designed by : T.K. HAREENDRAN
Source: www.efymag.com

Total Circuit details [Download]