Analog Hearing Aid

Analog hearing aids are dependable, well-established devices that enhance sound in a smooth and continuous manner. Unlike digital hearing aids, they amplify all incoming sounds uniformly, producing natural and uninterrupted audio that is comfortable for many users. In this project, you will learn how to build a simple analog hearing aid using basic electronic components and a rechargeable battery. The tutorial explains each step clearly from the fundamentals, making it easy for beginners to follow and successfully create their own analog hearing aid.

Resistors

1. R1 = 5.1 kΩ
2. R2 = 120 kΩ
3. R3 = 1.5 kΩ
4. R4 = 1.5 kΩ
5. R5 = 100 Ω
6. R6 = 10 kΩ
7. R7 = 680 Ω
8. R8 = 120 kΩ

Capacitors

1. C1 = 100 µF
2. C2 = 0.1 µF
3. C3 = 4.7 µF
4. C4 = 47 µF

Transistors

1. Q1 = KTC9014
2. Q2 = S9012-A
3. Q3 = KTC9014

Others

1. 3.5 mm Audio jack
2. 5 V Power supply
3. 4-Pin Switch

The microphone continuously listens to the surrounding environment.

When a person speaks or any sound is produced, sound waves travel through air and reach the microphone diaphragm.

Purpose:

To capture external sounds that the user cannot hear clearly.

The microphone converts the incoming sound waves into a very small electrical audio signal.

This signal represents the same pattern as the sound but at a very low voltage and current level.

Purpose:

To change sound energy into an electrical form that can be processed by the circuit.

A resistor supplies a DC bias voltage to the microphone.

This bias is essential for condenser/electret microphones to operate correctly.

Without biasing:

1. The microphone will not produce a usable signal
2. Sound pickup will fail

Purpose:

To allow the microphone to function properly and generate the audio signal.

The electrical signal from the microphone is extremely weak.

It is fed into the amplifier stage, where transistors amplify the signal to a higher level.

This stage increases:

1. Signal voltage
2. Signal strength

Purpose:

To make the sound signal strong enough for further processing and listening.

Capacitors in the circuit remove:

1. Power-supply noise
2. Unwanted high-frequency disturbances

They also stabilize the signal and block DC components between stages.

Purpose:

To ensure clear audio output without distortion or interference.

The amplified and filtered audio signal is delivered to the output stage.

This stage provides enough current to drive the earphone properly.

Purpose:

To prepare the signal for conversion back into sound.

The earphone converts the amplified electrical signal back into sound waves.

The user hears a louder and clearer version of the original sound.

Purpose:

To assist people with hearing loss by improving sound audibility.

A HW-167 lithium-ion charging module is integrated with a rechargeable battery to power the circuit.

Functions of the module:

1. Charges the battery safely
2. Provides stable DC supply
3. Enables portable operation

Purpose:

To eliminate frequent battery replacement and ensure reliable, continuous power.

All components are soldered onto a PCB and placed inside a small casing. The microphone, volume knob, charging port, and earphone jack are positioned for easy access.