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MT8870 DTMF Decoder Module

The MT8870 based DTMF (Dual Tone Multi-Frequency) decoder module is commonly used to control robots with a mobile phone, it is also used in different kinds of home automation projects where mobile dial pad input is required. This module works as a tone decoder that uses its 3.5 mm audio connector socket to get the input audio signal. It is popularly used for mobile and fixed telephone voice dialing and recording related functions.


MT8870 DTMF Decoder Module Pinout Description

Pin Name




Binary Bit 1



Binary Bit 2



Binary Bit 3



Binary Bit 4



Delayed String Output

Represents Binary Bit 0


Power Down Input



Inhibit Input

Logic high inhibits the detection of tones representing characters A, B, C and D


DC Supply Input

4.5V - 5.5V (5.0V Nominal)





Features of MT8870 Decoder Module

  1. Power Input: 5V Nominal (4.5V - 5.5V)
  2. Onboard 3.5mm jack input Facility
  3. MT8870 Based Frequency Decoder
  4. 5 Channel Interface
  5. Detects 0-9, A-D, *, #
  6. LED notifier for Output state
  7. 2.54” Pin pitch
  8. Board Dimension: 37 x 25 x 12 mm (l x w x h)


Note: Complete technical details on MT8870 Decoder IC can be found in the MT8870 Datasheet linked at the bottom of this page.


Alternative for MT8870: There are not many alternatives for MT8870, you can try SSI202 and M957 but they are no longer in production.


MT8870 DTMF Decoder Module - Overview

DTMF is commonly found in tone based dial pad devices such as mobile phones or telephones dial pad. When the dial pad is pressed, it produces a combination of two separate sine waves which is a unique frequency signal that can be decoded and produced as a binary output. MT8870 based DTMF module does exactly the same thing. The pressed button can easily be identified by checking the binary output. It can produce binary output by getting tone input from 0-9 number, A - D letters, * and # symbols. The important components on the MT8870 DTMF Module are marked below.

MT8870 DTMF Module

The binary output digits are available on the output pin Q1 to the pin Q4. In this module, there are onboard LEDs that can be very useful to identify the output state signal of the binary pins.


The DTMF module has a 3.5 mm audio input Jack that can be easily connected with a mobile phone by using a 3.5mm audio jack. It is very useful to add dual-tone multi-frequency decoding in any microcontroller based projects.


MT8870 Interfacing diagram

DTMF decoder modules can be interfaced with any kind of microcontroller like PIC, Arduino, etc. It requires 4 digital I/O pins to be interfaced with the 4 binary bit output pins. It also requires a 5 volt supply to the power of the module. In the below diagram, a simple interfacing example is shown where a generic microcontroller unit is shown.

MT8870 Interfacing Diagram



1.   Wired Robot control via mobile phone keypad.

2.   Home Automation

3.   Security Systems


2D Model

The dimensions of the MT8870 DTMF Module is shown below

MT8870 DTMF Module Dimensions

Component Datasheet

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