How to make DTMF Decoder: Electronics Project

Circuit diagram of DTMF decoder

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Components

1) Breadboard.

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

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2) 9V battery:

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3) four small LED:

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

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connecting wires and cutter:

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Resistors: 100K, 100K, 330K.

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

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Cellphone connector (If possible use NOKIA):

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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18) Connect your mobile to the audio jack.

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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.

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Watch YouTube video for this project.

https://www.youtube.com/watch?v=OF3SfGyvgbg

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13 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

  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 .

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