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    [Circuit][DTMF] Celphone DTMF decoder

    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:ckt.jpg


    Dilip

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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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.
    Learning is a continuous process.....

    Dhaval Mehta


    3 members found this post helpful.

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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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 ?



    •   Alt17th May 2011, 06:27

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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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.
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    Quote Originally Posted by mehtadhaval View Post
    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.
    any one earpiece would do ?



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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.
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    Quote Originally Posted by mehtadhaval View Post
    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.
    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



    •   Alt17th May 2011, 13:00

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    Re: [Circuit][DTMF] Celphone DTMF decoder

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

    headphone from creative i broke open
    Do you have a 3.5mm jack in your phone ?
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    Quote Originally Posted by mehtadhaval View Post
    copper is the ground and you can use anyone of the remaining wire......



    Do you have a 3.5mm jack in your phone ?

    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



    •   Alt17th May 2011, 14:16

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    Re: [Circuit][DTMF] Celphone DTMF decoder

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


    dec.gif

    Apply the headphone o/p to the "DTMF i/p" of the ckt.....
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    Quote Originally Posted by mehtadhaval View Post
    if your ckt is not working, then try this circuit :


    dec.gif

    Apply the headphone o/p to the "DTMF i/p" of the ckt.....
    wat should i do wid the 5th and 6th pin
    also what is the value of the capacitance ?



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    Re: [Circuit][DTMF] Celphone DTMF decoder

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

    also what is the value of the capacitance ?
    which capacitance are you talking about ??? the circuit contains only 2 capacitors and both are of 0.1 uF. And take R = 47k.
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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 ----------

    Quote Originally Posted by mehtadhaval View Post
    if your ckt is not working, then try this circuit :


    dec.gif

    Apply the headphone o/p to the "DTMF i/p" of the ckt.....
    not working



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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.
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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


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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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,
    Learning is a continuous process.....

    Dhaval Mehta



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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
    There are lot of fake ic's found in the market, especially dtmf decoder. Try a different chip from different dealer/shop.


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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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 ?



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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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.
    Learning is a continuous process.....

    Dhaval Mehta


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    Re: [Circuit][DTMF] Celphone DTMF decoder

    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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