These are the decoder output table for the given dial tone detected. A complete table of the decoded digital output for individual dial tone is available in the coming section. Output Logic behavior from the DTMF decoder IC.ĭetection 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. It is very interesting, and I will try to cover that aspect in near future.
#Mt8870 decode in codevisionavr software
DSP software algorithm can be implement to generate as well as to decode DTMF tone. Remote control to Home/Office electrical appliances using a telephone network.ĭTMF is a popular project especially in DSP (digital signal processing) subject. Many communication application can be build for example, a computerize call receiving/diverting phone network system. This circuit can be interface to a computer, allowing caller to computer interaction. This project article focus on a simple DTMF (dual tone multi-frequency) decoder circuit. 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 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. For example, the tone of 941hz + 1336hz will be decoded as binary '1010' as the output. On the telephone exchange side, it has a decoder circuit to decode the tone to digital code. The frequency use in the dial tone system is of audible range suitable for transmission over the telephone cable. Pressing key '9' will generate the tone form by 852hz & 1477hz. 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. When a key is being pressed on the matrix keypad, it generate a unique tone consisting of two audible tone frequency. Basically on the caller side, it is a dial tone generator. It uses electronics and computer to assist in the phone line connection. As more and more people find phone technology a useful communication tools, line connection use human operator has become a tedious task.Īs technology matures, pulse/dial tone method was inverted for telephony communication. 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.
In the early days, our phone system used to be operated by human operator in a telephone exchange room.