Problems with DTMF decoder . Help please!

Discussion in 'The Projects Forum' started by Kata, Jun 26, 2009.

  1. Kata

    Thread Starter New Member

    Jun 26, 2009
    hello !
    i have a problem with a school project . i have to send dtmf tones from my PC to MT8870 and display the dialed number.
    As BCD-7 seg dcd i used HCF 4511BE and an CC digit and a LM7805 for a 5V supply.
    Now, the thing is .. i was a litle confused on how to conect my decoder to the computer so i used an audio jack and inserted into the audio output of my comp.
    I tried to send "2" but nothing...the display showed 8 as it was when i just tested the circuit by conecting it only to the supply
    After a few hour i decided to try again and when i pluged in the circuit at 5V, the display showed 2 ..o_0.. only this time it was not conected to my computer .. just to the supply.
    So i thought ..ok.. the circit memorised the last signal that was sent .. but now i tried "3" and nothing it just displays "2"...

    i attached a pic. with the circuit . i apologise for the bad drawing. cand someone PLEASE just check it out and tell me if i did something wrong or if .. a pin is bad-coneccted.
    Thank u