DTMF Decoder 2

Posted on Feb 5, 2014

This device and all information contained on this website is for educational purposes only. This device must be used in conjunction with any and all local, provincial and federal laws. It is up to the end user to comply with all legal guidelines, thus we are not and will not be held responsible for any misuse of this product or any damages that it

DTMF Decoder 2
Click here to download the full size of the above Circuit.

may cause. The DTMF decoder 2 is a useful tool used for decoding DTMF (Dual Tone Multi frequency) generated by telephones. The decoded digits are viewed on a 16x2 LCD screen. The DTMF decoder can be directly connected to a Serial port to view the digits in HyperTerminal on a computer. The decoder stores the last 234 received digits in EEPROM. The contents of EEPROM can be viewed on the LCD screen via two scroll buttons. Total power consumption is 12mA. The DTMF decoder has two inputs. A RJ11 jack for connecting to the phone line and a 1/8" audio jack for connecting to a scanner, tape recorder or other audio output device. A PCB layout is provided if one wishes to construct their own PCB. Simply print the file at 1:1 onto an overhead transparency. (Get the correct sheet for your type of printer) I used a kit by MG Chemicals ( E-Sonic Search for 416-K) to produce my PCB. The provided PCB layout`s smallest traces are 15 thou wide. Drill the holes for the headers at 40 thou. Drill the holes for the 20K POT, the buttons, and the audio jack at 35 thou. Drill the rest of the holes at 30 thou. Drill bits can be found a most hobby stores. Review the schematic and parts placement diagram before beginning assembly for proper orientation of ICs and capacitors. Begin by installing the 7 jumper wires. Next solder in all the resistors and capacitors. Then solder in the buttons, the phone and audio jack, the 20K POT and the crystal....

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