DTMF decoder circuit is the circuit that has been utilized as a part of the last circuit to discover the number according to the double recurrence signal sent from the phone trade. It comprises of a MT8870 IC which is a DTMF decoder, a 18-pin IC that changes over simple DTMF sign to 4-bit parallel yield. This IC changes over simple DTMF signal from the phone into the comparing 4-bit computerized information in its pin 11 (LSB), 12, 13 and 14 (MSB) respectively.[4] Along with this information, 13 another data StD is nourished to the interfere with pin of the microcontroller. Pin 11, 12, 13 and 14 are twofold coded bits and sent to ports of the microcontroller. At the point when the StD pin is high then just the microcontroller takes the information from the DTMF decoder.

So also, the DTMF decoder unit has been utilized in our last circuit to produce a relating DTMF mix to the client's number if any security slip (fire in the house or interruption) has happened in the house. This is a unit that changes over the twofold coded signals into simple DTMF signals. The UM91215A IC is a 16-pin chip that takes the twofold flags from the microcontroller and conveys DTMF tones comparing to the number to be dialed.

The seven yield bits from the microcontroller are given to seven pins numbered 10 to 16 of the DTMF generator IC.[5] The IC then yields a DTMF tone which is the mix of the two frequencies (upper and lower band).