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DTMF Decoder Using MT In the early days, our phone system used to be operated by human operator in a telephone exchange room. The caller will pick. Dual-tone multi-frequency signaling (DTMF) is an in-band telecommunication signaling system . Two CMD CMCSI DTMF Receivers. DTMF was originally. Using MT DTMF Decoder With Arduino: DTMF DECODERS Are used to detect DTMF TONES Genrated by mobile phone DTMF this project we .

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This circuit detects the dial tone from a telephone line and decodes the keypad pressed on the tdmf telephone. The name was given because the tone that we heard over the phone is actually make up of two distinct frequency tone, hence the name dual tone.

The DTMF tone is a form of one way communication between the dialer and the telephone exchange. A complete communication consist of the tone generator and the tone decoder. These digital bits can be interface to a computer or microcontroller for further application eg.

In the early days, our phone system used to be operated by human operator in a telephone exchange room. The caller will pick up the phone, giving instruction to the operator to connect their line to the destination over the other end of the telephone. As more and more people find phone technology a useful communication tools, line connection use human operator has become a tedious task.

It uses electronics and computer to assist in the phone line connection. Basically on the caller side, it is a dial tone generator.

8870 DTMF decoder – output latch

When a key is being pressed on the matrix keypad, it generate a unique tone consisting of stmf audible tone frequency. The frequency use in the dial tone system is of audible range suitable for transmission over the telephone cable. On the telephone exchange side, it has a decoder circuit to decode the tone to digital code.


88870 digital output will be read in by a computer, which will then act as a operator to connect the caller’s telephone line to the designated phone line.

The telephone exchange center will generate a high voltage signal to the receiving telephone, so as to ring the telephone bell, to notified the receiving user that there is an incoming call. This project article focus on a simple DTMF dual tone multi-frequency decoder circuit. This circuit can be interface to a computer, allowing caller to computer interaction. It is very interesting, and I will try to dtnf that aspect in near future. For now we do the hardware way.

Very small, roughly about my thumb size.

Troubleshooting CM8870 DTMF Decoder Circuit

Logic 0 ‘1’ press and hold TOE: Logic 1 release from button ‘1’ TOE: 870 1 ‘2’ press and hold TOE: Logic 0 release from button ‘2’ TOE: Logic 0 ‘0’ press and hold TOE: Logic 0 Detection dtf dial tones is reflected on the bit TOE, while the output Q4, Q3, Q2, Q1 indicate the dial tone that is being detected on the telephony system. A complete table of the decoded digital output for individual dial tone is available in the coming section.

Notice that there are key tone for A B C and D.

These are special tone which are normally not found on our telephone. It is a common standard build into the decoder chip. The circuit is relatively simple and straight forward, and all components can be easily found. Schematics and BOM is provided below for your reference.

Troubleshooting CM DTMF Decoder Circuit | All About Circuits

You may purchase MT chips and 3. This LC Meter allows to measure incredibly small inductances making it perfect tool for making all types of RF coils and inductors. The circuit includes an auto ranging as well as reset switch and produces very accurate and stable readings.


The output waveforms can be both amplitude and frequency modulated.

The meter is a perfect addition to any power supply, battery chargers and other electronic projects where voltage and current must be monitored.

It is a very useful bench test equipment for 870 and finding out the frequency of various devices with unknown frequency such as oscillators, radio receivers, transmitters, function generators, crystals, etc. It can be connected to any type of stereo audio source such as iPod, Computer, Laptop, CD Player, Walkman, Television, Satellite Receiver, 870 Deck or other stereo system to transmit stereo sound with excellent clarity throughout your home, office, yard or camp ground.

It also analyzes transistor’s characteristics such as voltage and gain.

It is an irreplaceable tool for troubleshooting and repairing electronic equipment by determining performance and health of electrolytic capacitors. Dtmd amplifier is small enough to fit in Altoids tin box, and thanks to low power consumption may be supplied from a single 9V battery.

It’s small, power efficient, yet customizable through onboard 2 x 7 perfboard that can be used for connecting various sensors and connectors.

Arduino Prototype uses all standard through-hole components for easy construction, two of which are dtmv underneath IC socket. You can control lights, fans, AC system, computer, printer, amplifier, robots, garage door, security systems, motor-driven curtains, motorized window blinds, door locks, sprinklers, motorized projection screens and anything else you can think of.


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