Circuit Operation Principle The deaf hearing aid circuit consists of a microphone BM, a resistor Rl, R2, a capacitor Cl-C4, a potentiometer RP, an audio power amplifier integrated circuit lC, a power switch S, a battery GB and an earphone BE, as shown in Figure 9-78. Show.
The BM converts the picked-up sound signal into a weak electrical signal, and then adds it from the 7th pin of the IC via Cl and RP, and the audio power is amplified by the IC circuit; the sound is restored through the earphone.
Changing the resistance of the RP can change the volume of the headphones.
Component selection
Both Rl and R2 use 1/8W metal film resistors.
The RP uses a small synthetic carbon film potentiometer with a switch (power switch S).
Cl uses monolithic capacitors; both C2 and C3 use ultra-small aluminum electrolytic capacitors with a withstand voltage of lOV.
The IC uses TDA2822 or D2822 type audio power amplifier integrated circuit.
BM uses ultra-small high-sensitivity electret microphones.
The BE uses 8Ω stereo headphones (parallel).
GB uses two 7-cell batteries.
The BM converts the picked-up sound signal into a weak electrical signal, and then adds it from the 7th pin of the IC via Cl and RP, and the audio power is amplified by the IC circuit; the sound is restored through the earphone.
Changing the resistance of the RP can change the volume of the headphones.
Component selection
Both Rl and R2 use 1/8W metal film resistors.
The RP uses a small synthetic carbon film potentiometer with a switch (power switch S).
Cl uses monolithic capacitors; both C2 and C3 use ultra-small aluminum electrolytic capacitors with a withstand voltage of lOV.
The IC uses TDA2822 or D2822 type audio power amplifier integrated circuit.
BM uses ultra-small high-sensitivity electret microphones.
The BE uses 8Ω stereo headphones (parallel).
GB uses two 7-cell batteries.
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