MT8870 DTMF Voice Decoding Module

Rp115.000



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Deskripsi

Descriptions :

This circuit detects the dial tone from a telephone line and decodes the keypad pressed on the remote telephone. The dial tone we heard when we pick up the phone set is call Dual Tone Multi-Frequency, DTMF in short. 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. In this article, we are use the IC MT8870DE, the main component to decode the input dial tone to 5 digital output. These digital bits can be interface to a computer or microcontroller for further application eg. remote control, phone line transfer operation, LEDs, etc…

Specifications :

1. On-board MT8870 frequency decoder chip.
2. On-board voice input interface.
3. On-board five LED light, convenient to check the output state.
4. The basic have lead to chip mainly tube feet.
5. PCB size: 26.5mm x 24.5mm.

DTMF DECODER SCHEMATIC

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.

As technology matures, pulse/dial tone method was inverted for telephony communication. It uses electronics and computer to assist in the phone line connection. Basically on the caller side, it is a dial tone generator. When a key is being pressed on the matrix keypad, it generate a unique tone consisting of two audible tone frequency. For example, if the key ‘1’ is being press on the phone, the tone you hear is actually consist of a 697Hz & 1209Hz sine signal. Pressing key ‘9’ will generate the tone form by 852Hz & 1477Hz. 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. For example, the tone of 941Hz + 1336Hz will be decoded as binary ‘1010’ as the output. This 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. Many communication application can be build for example, a computerize call receiving/diverting phone network system. Remote control to Home/Office electrical appliances using a telephone network.

DTMF is a popular project especially in DSP (digital signal processing) subject. DSP software algorithm can be implement to generate as well as to decode DTMF tone. It is very interesting, and I will try to cover that aspect in near future. For now we do the hardware way.

Output Logic behavior from the DTMF decoder IC.

no button press
TOE: Logic 0
Q4: Logic 0
Q3: Logic 0
Q2: Logic 0
Q1: Logic 0

‘1’ press and hold
TOE: Logic 1
Q4: Logic 0
Q3: Logic 0
Q2: Logic 0
Q1: Logic 1

release from button ‘1’
TOE: Logic 0
Q4: Logic 0
Q3: Logic 0
Q2: Logic 0
Q1: Logic 1

‘2’ press and hold
TOE: Logic 1
Q4: Logic 0
Q3: Logic 0
Q2: Logic 1
Q1: Logic 0

release from button ‘2’
TOE: Logic 0
Q4: Logic 0
Q3: Logic 0
Q2: Logic 1
Q1: Logic 0

‘0’ press and hold
TOE: Logic 1
Q4: Logic 1
Q3: Logic 0
Q2: Logic 1
Q1: Logic 0

Detection of 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.

Key Tone Output Logic
Q4 Q3 Q2 Q1
1 0 0 0 1
2 0 0 1 0
3 0 0 1 1
4 0 1 0 0
5 0 1 0 1
6 0 1 1 0
7 0 1 1 1
8 1 0 0 0
9 1 0 0 1
0 1 0 1 0
* 1 0 1 1
# 1 1 0 0
A 1 1 0 1
B 1 1 1 0
C 1 1 1 1
D 0 0 0 0

These are the decoder output table for the given dial tone detected. 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.

MT8870 DTMF Voice Decoding Module

Informasi Tambahan

Berat 0.001 kg
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