Welcome to this very simple page on how to see if your DTMF decoder is Receiving the DTMF tones by flashing a LED.
Now if you would like to see my unit flashing when I send the tones from my Cell phone then visit my You Tube page here.
Now if you have come to this page first then go back to the start of this project click here.
I set this page up as a number of people have asked about this for there own DTMF devises all you need is one LED and one resister.
Now look at the 8870 DTMF chip on your DTMF decoder board you will see it has 18 pins on it you need to solder a 1K ohm resister or similar to pin 15 be careful not to get solder on the pins next to pin 15.
Now with the second end of the resister solder this to the LED's Longest lead the anode + see photo below of the LED.
Now Solder the second lead of the LED to the Ground Return or Negative pin on the decoder board,
How this very simple LED switches on is when you press the keys on your cell phone or what ever you are using to send the DTMF tones, The 8870 Chip decodes the tones and on pin 15 gives five volts output this gives a very good indication your unit is receiving the DTMF tones ok.