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MT8870 DTMF Decoder

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dramrattan

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Hi,

I implemented this circuit and it works fine but now that i have to demonstrate it soon i don't know why each part was choosen as the values seen in the circuit.

From reading the MT8870 DTMF decoder datasheet i know its the differential input configuration used and that gain setting can be used...Why does it need a gain and how dto calculate these values shown?
 

shahtejasm

New Member
Hi,

I implemented this circuit and it works fine but now that i have to demonstrate it soon i don't know why each part was choosen as the values seen in the circuit.

From reading the MT8870 DTMF decoder datasheet i know its the differential input configuration used and that gain setting can be used...Why does it need a gain and how dto calculate these values shown?
i have also completed.
but i want to know how i get indication of dialled no person receives calls or not on micrcontroller??

please reply....
 

dramrattan

New Member
Looking back at your question carefully...you kinda confuse me at what you exactly want...do you want to know how to get the number beind dialled?
 

shahtejasm

New Member
DTMF Decoder

hi,

I want to get time duration of call.
so i need some indication whether dialled no person pick the receiver or not??
 

dramrattan

New Member
hi

Sorry for responding so late...Here is the code...Should tell you how to get the duration of calls but its an estimate...I created functions to count secs, mins, and hour. To get the actual exact duration you would need to determine when the person lifted the receiver on the other end. In some networks, this is detected by a polarity reversal of TIP and RING...You could use my timing if you require just an estimate and not the exact timing.

Ragards.
 

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