Automated Hearing Aids Project

As a part of our ICCD project, we had designed automated hearing aids. I hope that many of you had designed an amplifier and you all have a basic idea that hearing aids are nothing but an amplifier. If you are looking to make a project of an amplifier which is very easy to make and you would easily make it with the help of a few transistors or op-amp or any other ic's. But what if we make automated hearing aids by using hardware without using any software part. So this project is fully hardware-based. Below there is a block diagram of this project I will explain to you each and every block step by step.

Block Diagram:-

Circuit Diagram:-

Components Required:-
1) Mic (Electret Condenser mic)
2) 2 BJT transistors (bc547)
3) Op-Amp (Ic 741)
4) Controller or timer circuit (Ic NE555)
5) Capacitors and Resistors (Values are provided in the circuit diagram)
6) Two 5v cells

Working:-
1) Mic:-

As we all know the mic is a transducer because it converts sound energy into electrical energy. The mic that we are using is an electret condenser microphone. It is not that much sensitive, it's sensitivity is around 6mv/Pa to 18mv/Pa. So we had designed an amplifier by considering the output of the mic as 10mv. As you can see that the output of the mic is going to the pre-amplifier and buffer amplifier. So we will go with pre-amplifier, comparator, timer circuit(NE555) and then we will see buffer amplifier and at the end amplifier.

2) Pre-Amplifier:-

It is just a normal ce amplifier(transistor bc547) that will amplify a few mv of signal to volts. I had designed it in such a way that if the output of the mic is greater than or equal to 10mv(pk-pk) then the output voltage of the pre-amplifier would be around 3v(pk-pk). If you want to see how I designed it then visit this post designing of ce amplifier. Now you would be thinking that why we want this pre-amplifier stage?. Your this doubt would be cleared in the next stage that is Comparator.

3) Comparator:-

For those who are new to the comparator, I had explained the concept of the comparator in the video given below. So for now just remember that comparator just compares the 2 inputs i.e. voltage coming from pre-amplifier and variable resistor. Now, the variable resistor is used to get proper sensitivity.

NOTE :- Here +Vcc = 5v & -Vcc = -5v
If the voltage of the pre-amplifier(Vp) is greater than the voltage of variable resistor(Vr) i.e. [Vp > Vr] then the output of the comparator would be -Vcc in our case it is -5v
Similarly, if the voltage of the pre-amplifier(Vp) is less than the voltage of variable resistor(Vr) i.e. [Vp< Vr] then the output of the comparator would be +Vcc in our case it is +5v.
Since for comparing we need both the inputs in volts so that's why we are using pre-amplifier so that it will convert millivolts of the signal into volts.

4) Timer Circuit or Controller:-

The output of the comparator is given to pin number 2 of NE555 ic. Ic555 is the heart of this project. We are using NE555 for this project because our output is dependent on time and we are using it in a monostable state. So I will just explain in short what is NE555 controller.I hope everyone knows about not gate which produces an inverted output to that of input. If we give logic'0' at the input of not gate we get logic'1' at the output. The NE555 Ic works very much similar to not gate but here we have that privilege to set the time for which the output would be high.
When NE555 gets -5v at its pin number 2 then at the output i.e. at pin number 3 of NE555 we get +5v for 1sec which means I had selected the values of resistor and capacitors such that we will get +5v at pin number 3 for 1 sec even if the input signal is of few microvolts. The formula for calculating the time period is t = 1.1*R*C.
Before going to the next block just remember that if the interval between two negative waves is less than at the output we will get a steady-state positive pulse i.e. pure dc as shown below.

5) Amplifier:-

Right now just to save time we had kept the values of the amplifier  same as that of the pre-amplifier. But as we know the task of the amplifier is to amplify the input signal. We had used Bjt transistor to make this amplifier which is amplifying 10mv of the signal you can use fets and Op-Amps as well. Ic555 is the heart of this project then this amplifier is the brain of the project. The output of Ic555 acts as a supply voltage for this amplifier i.e. (Vcc=+5v). If the output of Ic555 is logic'1' then only the amplifier will amplify the input signal else it won't.

6) Buffer Amplifier:-

To avoid maximum loss of the input signal we are using a buffer amplifier. Let's say the output of mic is 10mv so ideally at the input of amplifier we should get 10mv but practically we won't get that 10mv might be we will get 7mv which means we are loosing 3mv of the signal. But when we connect buffer amplifier we might get 8.5mv of a signal at the input of the amplifier although we are losing 1.5mv signal from that 10mv of signal but if you compared above where you were not using buffer amplifier there you were losing 3mv. So the buffer amplifier provides power to that particular part.

Pcb Designing:-
Click on the link given below to get the Gerber File of this project

VIDEO:-
Please do watch the video because I had explained the simulation of this project in this video. I hope you will understand it.
Part 1:-

Part 2:-

The project is done and edited by
Swarit Mahalsekar:- 18105A0005
Sanika Thakur:- 18105A0013

For any query or any further improvement regarding this project, you can CONTACT US.
or you can also comment below.