Decoder Device 2 for Dual Tone Multi Frequency

Decoding the telephone-generated DTMF is the purpose of building the DTMF decoder 2 which can be connected directly to a serial port and use a HyperTerminal on a PC to view the digits.

A 16×2 LCD screen is used to view the decoded digits and the contents of EEPROM through the 2 scroll buttons. The last 234 received digits in EEPROM are stored by the decoder as the device consumes 12mA of total power. There are two inputs that are employed by the DTMF decoder which include a 1/8” audio jack for connecting to a tape recorder, scanner, and other audio output device and an RJ11 jack for connecting to the phone line.

In the second revision, the changes made include removing the useless microphone circuit while the C language is used to write the program. The power consumption of the device was improved to 12mA from the 21.7mA. The ‘*’ and ‘#’ characters will be properly displayed while the line number from 1-19 is displayed when scrolling. The contact de-bounce button will be filtered from the software and most importantly, direct to PC connection is possible without an interface.

Rest of the project