[SOLVED] [Circuit][DTMF] Celphone DTMF decoder

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dilip.dmn

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Hi guys,
I have been trying to generate a DTMF decoder over the mobile phone.I am not interested in Landline because my motive is to generate a circuit for home automation and mobile robot.So i need to have a system to decode the DTMF generated by the mobile phone recieving end.:?:


I am attaching the DTMF decoding circuit that I was able to google out in the internet.

I am basically a Dummy and want to start with the electronic projects.So Please guide me over the cause.

Circuit:


Dilip
 

The circuit looks okay....
If you have a hands-free of the mobile phone, then cut the wire near earpiece. This way you will get 2 wires. One of them is common and the other is earpiece output. Now, connect the common wire to the ground of the circuit and remove the Mic from the circuit and connect the earpiece wire to the 100k resistor on the pin 2 of MT8870, and check the circuit by pressing the keys on the mobile phone.
 
u mean to say that i can remove that LM358 part of the circuit ?
The way you have guided me relies on opening the phone right,and getting the wires from the ear piece.
It solves a major part of the circuit but is there any other solution to this part without breaking open the phone ?
 

If you're using mobile phone, you can remove the LM358 part.
Also, I am not asking you to break the phone open. You just have to cut the "Hands-free" (earphone) that comes with the mobile, not the phone itself.
 

mehtadhaval said:
If you're using mobile phone, you can remove the LM358 part.
Also, I am not asking you to break the phone open. You just have to cut the "Hands-free" (earphone) that comes with the mobile, not the phone itself.
Click to expand...

any one earpiece would do ?
 

Yes, any earpiece would do.
And, before cutting the earpiece, make sure that when you press a button on the mobile phone, you can listen a tone in the earphone.
 

mehtadhaval said:
Yes, any earpiece would do.
And, before cutting the earpiece, make sure that when you press a button on the mobile phone, you can listen a tone in the earphone.
Click to expand...

ya i got hold of a working earphone...i cut the wire
the new problem is it has three leads and all three gving me an output voltage :-(
copper,blue,pink are the colours...

headphone from creative i broke open
 

copper is the ground and you can use anyone of the remaining wire......

headphone from creative i broke open
Click to expand...

Do you have a 3.5mm jack in your phone ?
 

mehtadhaval said:
copper is the ground and you can use anyone of the remaining wire......



Do you have a 3.5mm jack in your phone ?
Click to expand...


ya i do have 3.5mm jack

---------- Post added at 18:46 ---------- Previous post was at 18:45 ----------

but the circuit i did in the bread borad is not working i am not gting the led lit
 

if your ckt is not working, then try this circuit :




Apply the headphone o/p to the "DTMF i/p" of the ckt.....
 

wat should i do wid the 5th and 6th pin
Click to expand...
they have internal pull-downs, so just leave them unconnected.

also what is the value of the capacitance ?
Click to expand...

which capacitance are you talking about ??? the circuit contains only 2 capacitors and both are of 0.1 uF. And take R = 47k.
 

is there anyway that i can test the working of this chip...i dnt know why i am not gting any LED lit

---------- Post added at 13:37 ---------- Previous post was at 13:01 ----------
mehtadhaval said:
if your ckt is not working, then try this circuit :


View attachment 56367

Apply the headphone o/p to the "DTMF i/p" of the ckt.....
Click to expand...

not working :-(
 

check all the voltages on the circuit.
Also, make sure that you can hear the tones in the headphone before connecting the wires to the circuit.
And if that doesn't work, try calling the phone (the one connected to the ckt through headphone) and press the buttons from the other phone. And, if that doesn't work, then try building the circuit on general purpose PCB.
 

i dont knw if i am dnd andything wrong but i am not gting the led lit

is there anyway yo check if the chip is working ?mayb tats wat tat has gone wrong :-(

dont use sms or short hand typing skills in this forum... type the complete words by spending few more seconds. this is the last warning and further posts and thread of yours will be deleted without informing you if continued
Click to expand...
 
Last edited by a moderator:

This circuit itself checks the IC. If everything else is correct and this circuit is not working, then the IC may not be working. But, still I think that this is not because of the IC, you're missing something somewhere,
 

i dont knw if i am dnd andything wrong but i am not gting the led lit

is there anyway yo check if the chip is working ?mayb tats wat tat has gone wrong
Click to expand...

There are lot of fake ic's found in the market, especially dtmf decoder. Try a different chip from different dealer/shop.
 
sorry for the forum moderaters.was just too used to short messaging hence.



i dont know wat i am doing wrong.
3.5mm jack output is not at allshowig any variations,when idle and connected to signal dtmf or a music input.
what will be the real output under working condition ?
 

are you observing the o/p on the volt meter ???
Mostly the o/p is only 1 VPP max, so it is hard to observe the o/p on the voltmeter.
One other thing , did you remove the enamel on the copper wires of headphone ? In most of the headphones, the copper wires are insulated with enamel. So this can also cause the problem.
 
i have completed the circuit..succesfully

have attached the circuit that worked for me


Thank You


Now going in for designing a PCB myself.
 

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  • DTMF Decoder.pdf
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