How to make DTMF Decoder: Electronics Project

Circuit diagram of DTMF decoder



1) Breadboard.


2) IC 7805 and IC MT8870 (DTMF IC):


2) 9V battery:


3) four small LED:


Capacitors: 1) 0.1uF 2) 22pF 3) 22oF 4) 10uF


connecting wires and cutter:


Resistors: 100K, 100K, 330K.


Crystal Oscillator (KDS 3.5795)  i.e. 3.57MHz


Cellphone connector (If possible use NOKIA):


1) Step 1:  Insert the DTMF IC (MT8870) in the breadboard.


2) Step 2: Ground pin no 5, 6 and 9.


3) Step 3: Now connect the four LED’s to pin no 11, 12, 13, 14 with respect to ground.


4) Step 4: Connect two 22pF capacitors to pin no 7 and 8 with respect to ground (Don’t worry it has no polarity)


5) Step 5: Connect a crystal oscillator to pin no 7 and 8.


6) Step 6: Short pin no 1 and 4.


7) Step 7: Insert IC 7805 anywhere on the breadboard.


8) Step 8: 330K resistor between pin no 16 and 17.

18 19

9) Step 9: Connect 0.1uF capacitor to pin 17 with respect to 5V.


10) Step 10: Connect pin 10 and 18 to 5V


11) Step 11: 100K resistor between pin 2 and 3.


12) Step 12: Connect one pin of 100K resistor to pin 2 and leave other for next step.


13) Step 13: Connect negative end of 10uF (50V) capacitor to another end of 100K resistor and leave +ve terminal for next step.


14) Step 14: Connect a mobile headphone jack (+ve) to the positive terminal of capacitor and other terminal grounded.


15) Step 15: Make proper grounding by connecting wire.


16) Step 16: Connect the 9V battery to 7805 IC. Middle terminal to ground.


17) Step 17: 5V output given by 7805IC is connected to uppermost row.


18) Connect your mobile to the audio jack.


19) Press any key on Keypad you will see corresponding BINARY number of that digit. Please make sure that your keypad tones are ON ( To make keypad tones ON go to Settings>Tones>Keypad tones>ON)

30Thank you.

You can contact me on facebook:

Like our facebook page: for future updates.

Watch YouTube video for this project.

You may also like:

If you like this article, please share it with your friends and like or facebook page for future updates. Subscribe to our newsletter to get notifications about our updates via email. If you have any queries, feel free to ask in the comments section below. Have a nice day!

20 thoughts on “How to make DTMF Decoder: Electronics Project”

  1. while seeing this,i selected this as my mini project for the 6th semester,

    but when all the connections are done succesfully,the 4 led’s are ON but they do not change with keypad keys

    please help me ,its urgent..

  2. good project.

    Can I to change the 100K resistor to improve sensitivity? what do you recommend to do it?

    best regards

    1. Connect the circuit as same given then use any phone and make a call and try both mobile keypad during call…. it will definitely work…

  3. Everything is working bt when i call from another phone and dial number on that phone no response .. Bt it works only with the connected phone… What should i do?

  4. my project is complete as shown as above circuit diagram but it is not working , i give him 5.5 v dc , so please give me suggestion , in my circuit connected crystal oscillator is 11.0592MHZ .

  5. How to get a mobile connector? Can I use headphones as mobile connector..Though l gave connections as per the circuit diagram, I couldn’t get output…can we use any type of phone i.e touchscreen or button type

Leave a Reply