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[SOLVED] DTMF decoder using ic mt8870

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mihir08

mihir08

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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 .
dtmf.JPG



Today while browsing eda i also got this ckt .
New Bitmap Image (4).JPG



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
 

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.
 
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 .dtmf.JPG

c1 and c2 are 0.1 uf ... i missd the decimal in the image
 
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ramza038 said:
Plz mail me ur working MT8879 schematic. My email is ramza038@googlemail.com
Click to expand...

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.
 

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

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

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

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