Advance Electronics

DTMF Dual Tone Multi Frequency, MT8870DE DTMF Decoder

DTMF Description:


DTMF “Dual Tone Multi-Frequency”– In this tutorial, you will learn how to use the MT8870DE DTMF Decoder IC with any cell phone and control different electrical loads from anywhere around the world, by simply pressing keys on your cell phone. While using the MT8870DE DTMF Decoder there is no need to write a message. This can be used just like the Wireless Radio Transmitters and Receivers. You can use this to control a robot, an airplane, electrical loads, etc, in real-time.

A project based on the DTMF “Dual Tone Multi-Frequency” that I am about to share with you guys is one of my first top 20 projects; I created when I just started learning Electronics. In this project, you will learn how to control different types of electrical loads “DC or AC” using the famous MT8870DE DTMF Tone Decoder IC.  In this project no programming is needed, all you need is the MT8870DE DTMF Tone Decoder IC.

Before, I am going to explain the DTMF technology, complete circuit diagram, and other details; first, I would like to tell you how this project works. One cell phone is connected with the MT8870DE DTMF Tone Decoder IC through an audio jack. You will do some settings in the phone which is connected with the MT8870DE IC, that is, the cell phone should be able to automatically attend the call, you can activate this easily, and this is available in the cell phone settings.

Now, all you need is to make a call using any cell phone. The receiver cell phone will automatically attend the call, now you can press numbers on the cell phone keypad and you will be able to control the 12V relays connected with the MT8870DE DTMF Tone Decoder IC.

I will go through all the details covering,

  • About the DTMF Technology
  • Commonly asked questions
  • MT8870 DTMF decoder IC specs
  • MT8870 DTMF based PCB board, DIY.
  • How to use it directly to control electrical loads
  • How to use it with Arduino

Without any further delay, let’s get started!!!

The components and tools used in this project can be purchased from Amazon, the components Purchase links are given below:

MT8870DE DTMF Decoder

MT8870DE DTMF Decoder Ready Made module

One-Channel Relay Module:

Other Tools and Components:

Super Starter kit for Beginners

Digital Oscilloscopes

Variable Supply

Digital Multimeter

Soldering iron kits

PCB small portable drill machines

*Please Note: These are affiliate links. I may make a commission if you buy the components through these links. I would appreciate your support in this way!

About the DTMF “Dual Tone Multi-Frequency” Technology:

Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed in the Bell System in the United States and became known under the trademark Touch-Tone for use in push-button telephones supplied to telephone customers, starting in 1963. DTMF is standardized as ITU-T Recommendation Q.23. It is also known in the UK as MF4.

The Touch-Tone system using a telephone keypad gradually replaced the use of the rotary dial and has become the industry standard for landline and mobile service. Other multi-frequency systems are used for internal signaling within the telephone network.

DTMF Telephone Keypad:


The DTMF telephone keypad is laid out as a matrix of push buttons in which each row represents the low-frequency component and each column represents the high-frequency component of the DTMF signal. The commonly used keypad has four rows and three columns, but a fourth column is present for some applications. Pressing a key sends a combination of the row and column frequencies.


For example, the 1 key produces a superimposition of a 697 Hz low tone and a 1209 Hz high tone. Initial pushbutton designs employed levers, enabling each button to activate one row and one column contact. The tones are decoded by the switching center to determine the keys pressed by the user.

Ever noticed? How does the telephone operator know which button is pressed on your cell phone? The telecommunication network knows all this just because of the keys frequencies.

Some of the most commonly asked questions and their answers

What is DTMF used for?

Dual-tone multi-frequency (DTMF) is a method used to dial telephone numbers or to issue commands to switching systems. DTMF is widely used for telecommunication signaling between telephone handsets and switching centers over analog telephone lines in voice-frequency bands.

What is mean by DTMF?

dual-tone multi-frequency

DTMF (dual-tone multi-frequency) is the signal to the phone company that you generate when you press an ordinary telephone’s touch keys. In the United States and perhaps elsewhere, it’s known as the “Touchtone” phone (formerly a registered trademark of AT&T). DTMF has generally replaced loop disconnect (“pulse”) dialling.

How Does DTMF work?

DTMF keypad is placed out on a 4 cross 4 matrices, in which each row represents low frequency, each column represents high frequency, with DTMF, each key passed on a phone generates two tones of the specific frequencies one tone is generated from high-frequency tones and low-frequency tone.

What’s DTMF on a cell phone?

Dual-tone multi-frequency (DTMF) tones are used by automated dial-in systems such as voicemail or where prompts are used to navigate. (located in the upper right). Tap Call Settings. Tap DTMF tones.

What is DTMF write down the application of DTMF?

The applications of DTMF keypads almost include in mobile phones and landlines. Therefore this keypad is used for recognizing the dialed number by the caller in the telephone exchange rooms. The DTMF decoder like MT8870DE differentiates the tones of DTMF & generates the binary series equal to a key pushed in a keypad of DTMF.

Do cell phones use DTMF?

DTMF is the global standard for audible tones that represent the digits on a phone keypad. Mobile phone networks use digital signals instead of DTMF for direct dialing, but DTMF is still used over mobile phones to navigate automated systems such as phone menus, and for secondary dialings, such as using a calling card.

What does DTMF mean on a cell phone?

Dual-tone multi-frequency

DTMF decodes and encodes DTMF (Dual-tone multi-frequency) tones trough the phones speaker and microphone.

Why does DTMF use two tones?

DTMF ( Dual Tone Multiple Frequency ) is used to send to signals for button presses on telephones. The data is typically sent over voice channels and so in order to distinguish from a human voice, when you hit a button the phone generates two tones of different frequencies – one lower frequency and one high frequency.

What are DTMF tones in Jio phone?

DTMF (dual-tone multi-frequency) is the signal to the phone company that you generate when you press an ordinary telephone’s touch keys. In the United States and perhaps elsewhere, it’s known as Touchtone” phone (formerly a registered trademark of AT&T).

Are cell phones touch-tone phones?

Touchtone. The international standard for telephone signaling utilizes dual-tone multi-frequency (DTMF) signaling, more commonly known as touchtone dialing. It replaced the older and slower pulse dial system. The push-button format is also used for all cell phones, but with out-of-band signaling of the dialed number.

What is the difference between tone and pulse dialing?

Almost all telephone networks in today’s world use tone dialing. It is the method of pressing buttons, and those buttons make a sound. Pulse dialing is the system used on old rotary phones. While traditional landline phone networks widely support the format, many VoIP phone systems no longer support the format.

MT8870DE Dual Tone Multi-Frequency Decoder IC:


The MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the bandsplit filter and digital decoder functions. The filter section uses switched capacitor techniques for high and low group filters; the decoder uses digital counting techniques to detect and decode all 16 DTMF tone-pairs into a 4-bit code.

MT8870D Features

  • Complete DTMF Receiver
  • Low power consumption
  • Internal gain setting amplifier
  • Adjustable guard time
  • Central office quality
  • Power-down mode
  • Inhibit mode
  • Backward compatible with MT8870C/MT8870C-1

MT8077DE Applications

  • Receiver system for British Telecom (BT) or CEPT Spec (MT8870D-1)
  • Paging systems
  • Repeater systems/mobile radio
  • Credit card systems
  • Remote control
  • Personal computers
  • Telephone answering machine

MT8870DE Pinout:


MT8870DE Pin Description:

IN+: Non-Inverting Op-Amp  (Input).

IN-: Inverting Op-Amp   (Input).

GS: Gain Select. Gives access to the output of front end differential amplifier for the connection of feedback resistor.

VRef: Reference Voltage (Output).

INH: Inhibit (Input).  Logic high inhibits the detection of tones representing characters A, B, C and D. This pin input is internally pulled down.

PWDN: Power Down (Input).  Active high. Powers down the device and inhibits the oscillator. This pin input is internally pulled down.

OSC1: Clock  (Input).

OSC2: Clock  (Output) . A 3.579545 MHz crystal connected between pins OSC1 and OSC2 completes the internal oscillator circuit.

VSS: Ground (Input). 0 V typical.

TOE: Three State Output Enable (Input). Logic high enables the outputs Q1-Q4. This pin is pulled up internally.

Q1-Q4: Three State Data (Output). When enabled by TOE, provide  the code corresponding to the last valid tone-pair received .When TOE is logic low, the data outputs are high impedance.


StD: Delayed Steering (Output).Presents a logic high when a received tone-pair has been registered and the output latch updated; returns to logic low when the voltage on St/GT falls below VTSt.

ESt: Early Steering (Output). Presents a logic high once the digital algorithm has detected a valid tone pair (signal condition). Any momentary loss of signal condition will cause ESt to return to a logic low.

For more details download MT8870DE datasheet:

MT8870DE DTMF Decoder for controlling electrical loads:


Download PCB of the electrical loads control system using MT8870DE:

In the above image, it is hard to see the details of the components, but you can see everything in the PCB board layout. This circuit board can be used to control electrical loads 220Vac or DC loads. This is totally up to you for what purpose you want to use this project.

Apart from this, the MT8870DE DTMF Tone Decoder IC can also be used with Arduino or any other controller boards. The MT8870DE Decoder IC can be used to give commands to the Arduino to control different electric circuits, motors, etc.

MT8870DE DTMF Decoder with Arduino:


Download PCB layout, MT8870DE with Arduino:

The relays can be connected with the Arduino. You can also replace relays with Optocouplers or Pull-up resistors.

I have used these circuits in different projects e.g. for controlling robots, controlling electrical loads, in different Arduino based projects. You can easily modify the PCB designs. I recommend you should build this circuit by yourself.

If you find this hard to built, you can purchase the readymade MT8870 DTMF Voice Decoder Decoding Module Telephone Voice Module for Arduino.


MT8870 DTMF Decoder Arduino circuit Diagram:


MT8870 Tone decode IC interfacing with Arduino is very simple; you only need a few wires. The power supply pins of the MT8870 DTMF module are connected with the Arduino’s 5V and Ground. The output pins of the MT8870 DTMF module are connected with the Arduino’s I/O pins which can be clearly seen in the circuit diagram above.

MT8870 Arduino Code / Programming:

If you have any questions regarding this article, let me know in a comment.

Photo Credits:

Engr Fahad

My name is Shahzada Fahad and I am an Electrical Engineer. I have been doing Job in UAE as a site engineer in an Electrical Construction Company. Currently, I am running my own YouTube channel "Electronic Clinic", and managing this Website. My Hobbies are * Watching Movies * Music * Martial Arts * Photography * Travelling * Make Sketches and so on...

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One Comment

  1. Hello my friend, any body can call the receiving number then touch any button to control my robot ?. Are there any idea ? to protect the operation by a passcode ?
    Thanks in adv.

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