Deaf hearing aid three

This example introduces a deaf hearing aid made by MC34119 type communication low-power audio amplifier integrated circuit. It has the advantages of high output gain, low noise, good sound quality and stable performance. It is suitable for patients with mild to moderate deafness.
Circuit Operation Principle The deaf hearing aid circuit consists of a sound amplifying circuit, a power amplifying circuit and a power indicating circuit, as shown in Figure 9-79.

The pickup amplification circuit is composed of a microphone BM, a transistor V, resistors R1-R4, and capacitors C1, C2.
The power amplifying circuit is composed of a volume potentiometer RP, a capacitor C3-C6, a resistor R5-R7, a power amplifier integrated circuit IC, a socket XS, a plug XP, and a headphone BE.
The power indicating circuit is composed of a current limiting resistor and a light emitting diode VL.
After the power switch S is turned on, the VL lights up, and the sound pickup amplifying circuit and the power amplifying circuit are energized. When there is sound from the outside, the BM converts the sound signal into a weak electrical signal, which is driven by the V buffer, the RP volume, and the IC power to drive the BE to make a sound.
When the battery CB is fully charged, the VL normally emits light; when the GB power is insufficient, the light emitted by the VL becomes weak, prompting the user to replace the new battery in time.
The volume should be adjusted according to the adaptability of the deaf patients. After the volume is adjusted, there is no need to adjust it.
Component selection
R1-R8 selects 1/4W or 1/8W metal film resistors.
RP uses a small synthetic carbon film potentiometer.
Cl, C2 and C5 are all selected ultra-small aluminum electrolytic capacitors with a withstand voltage of lOV; C3 uses high-frequency ceramic capacitors; C4 and C6 are both monolithic capacitors.
VL uses φ3mm green LED.
V selects S9013 or 3DG9013 type silicon NPN transistor, and its current amplification factor is required to be greater than or equal to 100.
lC selects MC34119 type audio power amplifier integrated circuit.
BM selects CM-l8W type electret microphone.
BE selects 8-1OOΩ headphones.