Sensors

Interfacing MT8870 DTMF Decoder Module with Arduino

Written by Mehran Maleki

MT8870 DTMF Decoder Module Features

DTMF stands for Dual-tone-multi-frequency. This module is for sending signals using the voice-frequency band over telephone lines to switching centers. This module has two important applications: First, to specify the desired number to telecommunication through switching centers; second, it is capable of transmitting commands to these centers and other telecommunication devices.

Technical specifications:

Input voltage: 5V
5mm input jack
LED to indicate the binary outputs status
Recognize numbers 0-9, letters A-D and symbols *, #

MT8870 DTMF Decoder Module Pinout

This module has 6 pins:

VCC: Module power supply
GND: Ground
Q[1-4]: Binary Output
EST: Early Steering (Output)
INH: Inhibit (Input)
TOE: Three State Output Enable (Input)

You can see the pinout of this module here.

Different modes in each pin represent different data. The following table shows different modes:

Required Materials

Hardware Components

Arduino UNO R3	×	1
MT8870 DTMF Decoder Module	×	1
Male to Female Jumper wire	×	1

Software Apps

Arduino IDE

Note

You need an AUX cable to interface this module.

Interfacing MT8870 DTMF Decoder Module with Arduino

Step 1: Circuit

The following circuit shows how you should connect MT8870 module to Arduino and to the mobile phone using the AUX cable. Connect wires accordingly.

Step 2: Code

Upload the following code to your Arduino.

   /*
MT8870-DTMF-Receiver-Module
Made on 09 Feb, 2021
Home

*/

void setup() {
  Serial.begin(9600);
  pinMode(3, INPUT);
  pinMode(4, INPUT);
  pinMode(5, INPUT);
  pinMode(6, INPUT);
  pinMode(7, INPUT);
}

void loop() {
  uint8_t number;
  bool signal;
  signal = digitalRead(7);
  if (signal == HIGH)     /*When DTMF tone is detected, STQ will read HIGH for the duration of the tone*/
  {
    delay(100);
    number = ( 0x00 | (digitalRead(3) << 0) | (digitalRead(4) << 1) | (digitalRead(5) << 2) | (digitalRead(6) << 3) );
    switch (number)
    {
      case 0x01:
        Serial.println("Pin Pressed: 1");
        break;
      case 0x02:
        Serial.println("Pin Pressed: 2");
        break;
      case 0x03:
        Serial.println("Pin Pressed: 3");
        break;
      case 0x04:
        Serial.println("Pin Pressed: 4");
        break;
      case 0x05:
        Serial.println("Pin Pressed: 5");
        break;
      case 0x06:
        Serial.println("Pin Pressed: 6");
        break;
      case 7:
        Serial.println("Pin Pressed: 7");
        break;
      case 0x08:
        Serial.println("Pin Pressed: 8");
        break;
      case 0x09:
        Serial.println("Pin Pressed: 9");
        break;
      case 0x0A:
        Serial.println("Pin Pressed: 0");
        break;
      case 0x0B:
        Serial.println("Pin Pressed: *");
        break;
      case 0x0C:
        Serial.println("Pin Pressed: #");
        break;
    }
  }
}

In this program, you can evaluate the performance of this module using the mobile keyboard. By touching each number 0 to 9 and also the # and * symbols, you can see them in the Serial Monitor.

The output is as follows:

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