Introduction: OP AMP BASED HEARING AID
In this instructable i am going to show you how you can build a simple hearing aid with an op amp. The device can amplify the sound up to 5 times.
The making of the hearing aid is also very simple and would not take more than an hour.
The output of the device is a little cracky due to the crude op amp used but for the cost it is made (that is less than 1$) the device is very appreciable.
Step 1: MATERIALS YOU WILL NEED
The materials you will require are very easy to source and inexpensive .
The materials are
1.An op amp (any would work but i am using the 741)
2. Audio jack
3. 0.1uf caps x2
4. ~4.7k ohms resistor x3
5.~1k ohm resistor x1
6. 2.2 mega ohm or higher value resistor (i used 10 megs)
7. Earphones (any would work)
8. Purf board (about 20x15 holes)
9. An electret mic (best is from a phone )
The tools you would be requiring are
1. Soldering iron
3.Wire cutters and strippers (you can always use a pair of scissor)
Step 2: THE MAKING AND THE SCHEMATICS
The schematics in the picture above may seem very complex to beginners but is actually very simple , if you are not able to read the schematics I recommend you to go to this site reading schematics which will help you read it.
Also I will give you an overview so you can go on with me. You may be ready with your breadboard and some wires and the materials and then
1.place the 741 ic in the center socket with the notch pointing away from you
2.the first pin is not connected
3.connect the positive end of the electrit mic to vcc (positive end is the one that is not connected to the body of the mic, you can find this out by testing with a multimeter or just see the traces that follow to the body. ofcourse the other one is negetive.)
4. the other end of the mic connects to the 4k7 resistor
5.the 4k7 's other end is grounded.
6. the point at where the mic and resistor meet is connected to the 1k resistor
7.the1k resistor is then connected to a 0.1uf cap
8. the 0.1uf is connected to pin 2 of the 741
9. the pin 2 of the 741 also connects to the pin 6 through a 1m ohm or higher value resistor
10. a voltage divider of 2 4k7 resistor is connected to the pin 3 of the ic
11. pin 4 is grounded
12. pin 5 is not connected
13.pin 6 earlier connected to the 1m ohm resistor is connected to the headphone through the 0.1 uf capacitor
14. pin 7 is connected to vcc
15. pin 8 is not connected
After doing this ,plug in your headphones and give power to the circuit.
Step 3: SOME TIPS AND TRICKS
Before going on to the working, I would like to tell you that since this is a sound related project i can't guarantee that the project will work for all of you. But don't get discouraged it is very easy to make it work. Here are some tips and tricks that will help you troubleshoot and get it right -
1. NOT SURE IF YOUR DEVICE IS WORKING-try speaking into the mic if you don't hear any sound then try blowing on it .We will learn later why blowing has better results.
2.THE SOUND OUT OF THE EARPHONES IS TOO NOISY - try increasing the value of the capacitor between the output and the earphones.
3. WHICH MIC SHOULD I GET?-the best mic would be out of a mobile phone but you can always buy a mic from an electronics store. Also remember not to peel off the filter even if it is tempting as it affects the sound quality tremendously.
4.IMPROVE SOUND QUALITY-this works with some mics, you can attach a capacitor between the leads of the mic this way the sound will become more boxy that is the time delay between the pulses of the sound will increase. In simple words the sound becomes more square wavy
5. INVERT THE VOLTAGE DIVIDER- if the sound on your device is faint then connect the positive end to the mic and the ground to the 4k7 resistor. Or else if the sound is loud enough then no need. But keep in mind this will reduce the sound quality.
APART FROM THIS ANY QUERIES CAN BE POSTED IN THE COMMENTS.
Step 4: THE WORKING
The working is simple it is
-firstly, the mic consists of two plates situated very close to each other. when a sound is produced then the disturbances in air cause the distance between the plates to change which produces a very minute voltage of about 0.002 volts.
-then this voltage is amplified by the op amp to about 2 or so volts which goes to the headphones.
-to learn about op amps go to op amps
-the basis is very simple and can be understood easily. If any doubts please ask me in the comments.
Step 5: TESTING
Plug in power and audio and you should hear sound in the earphones.
if any queries please post in the comments and I will reply to them
Also just to tell you the sound from the hearing aid will be a little cracky but for the cost with which it is made it is very efficient. This device was made by spending only one dollar. so please appreciate it rather than saying negative in the comments