[SOLVED] DTMF decoder using ic mt8870

[mihir08]

hi , i am making a dtmf decoder but facing lot of problem . i am using the following circuit from Mt8870 data sheet but it is not working . tried at least 10 -20 times .




Today while browsing eda i also got this ckt .




i am not sure if that will work . but will surely try . if any one has a working circuit please post back .


i think resistor between pin 2 and 3 has some problem in ckt1 . i checked o/p from my cellphone on college cro ,its fine but after 0.1uf cap it doesnt show anything . also i am using a cellphone to give i/p i hope no issues with that .
please guide how do i troubleshoot
awaiting for your replies .


cheers .always good to be on eda

 

[tpetar]

1. Check DTMF encoder first does he generate DTMF at all.
2. Check signal cable connection Out/In.
2. Use small ceramic cap for C1 & C2 (100nF).
3. Use thise values for resistors R1=100K R2=100K R3=300K.

 

[mihir08]

fiinallly ............... !!!! used the info abt r1 frm ckt 2in ckt1. i realized that vin maybe less in amplitude and replaced 100k by 4.7k and it works awsum .

c1 and c2 are 0.1 uf ... i missd the decimal in the image

 

[ramza038]

Plz mail me ur working MT8879 schematic. My email is ramza038@googlemail.com

 

[jsudrik]

Plz mail me ur working MT8879 schematic. My email is ramza038@googlemail.com

Folks,

I am trying to use differential input configuration instead of Mihir's single ended input configuration and I am getting pin 15 always high. Is this expected and it goes low on receiving valid input? I am not sure what I could be doing wrong. Circuit is properly connected.

 

[vignesh ssvv]

if u can post a full video for connecting mobile phone with dtmf decoder....it will be much helpfull....

 

[vishaletm]

Hello i am facing similar problem. And above circuit doesn't works.

 

[vignesh ssvv]

the circuit works fine. I think the problem is with the way you connected your headset with the decoder. The best way to connect your headset is 'remove the plastic cover over your headset's speaker and solder the two nodes in that speaker with the decoder ic ' this worked fine for me

 

[vishaletm]

I've got the circuit working. I don't know what was the problem, I redesigned the PCB and got it working.

Designed for gain=10
View attachment dtmf.BMP

 

[mihir08]

il soon repost a tutorial on http://www.tronicsnmore.blogspot.com

 

[harshsingh1000]

sir please help ........i m making a dtmf project according the applicatin circuit given in data sheet but its not working......plzz its urgent.....

 

[ravi9340]

this ckt is not working for me. o/p of decoder ic is always low... plz help