Circuit diagram of DTMF decoder
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.
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)
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Watch YouTube video for this project.
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