DTMF circuit with LM8705

Discussion in 'The Projects Forum' started by eng.altamimi, Nov 6, 2011.

  1. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    I have these project but is not working the DTMF (MT8870) i dont know why?
     
  2. bertus

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    Apr 5, 2008
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  3. SgtWookie

    Expert

    Jul 17, 2007
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    We won't be able to help you unless you give us a lot more information.

    Like, the schematic to your circuit, what it is and is not doing, and if there is anything different between your circuit and the schematic.

    It would help a lot if you could also post a photograph of how you built your circuit.
     
  4. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    [​IMG]


    l connect circuit by mobile headset but not working.

    The pawer suply by transformer 220V to 22V AC by these cerucit



    [​IMG]
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    1st question:

    Are you supplying 22VAC to the LM7805? I don't hope so. The AC needs to be rectified, smoothed and then you pass the obtained DC to the 7805. Should be similar to this:
    [​IMG]

    It would be interesting to know if 22VAC is really the maximum you can get out of the transformer. Under no load condition the DC would be very near to the maximum input voltage of the 7805. You also waste a good amount of power in the regulator.

    2nd question: How did you hook up your mobile headset to your circuit?
     
  6. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    22V AC connect to bridge then to LM8705

    I cute the spekar and connect to DTMF input or I use mic connected to DTMF input
     
  7. gerty

    AAC Fanatic!

    Aug 30, 2007
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    Just so we're talking about the same thing, you've posted "LM8705" twice, do you mean LM7805 ?
     
  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    What do you measure at Vdd and VRef , pin 18 and pin 4 of the DTMF decoder?

    Can you post a picture of what you have built?

    What exactly does the circuit do? Nothing? Or not what you expected?

    Do you have an oscilloscope to measure the input voltage level?
     
  9. JingleJoe

    Member

    Jul 23, 2011
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    Oh no, this is "one of those threads".
    Maybe the poster has some sort of linguistic impairment, but I get the feeling they may be beyond help. ... Or beyond my ability to understand them in order to help.
    I give you chaps credit for trying. Carry on the good work :)
     
  10. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    Sorry the IC is not same number the IC numbrr i used is MT8870

    Is it defrant than CM8870?
     
  11. bertus

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    Apr 5, 2008
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    Hello,

    The CM8870 and MT8870 seem to be compatable.

    I have attached BOTH the datasheets so you can compare them.

    Bertus
     
  12. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    this is my circuits is it correct th +5V and -5V same i connected to the circuits or I have to but Ground to the circuits ?
     
  13. praondevou

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    Jul 9, 2011
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    It looks correct, except for the fact that -5V shouldn't be called "-5V" but "Gnd" or "zero".

    Check if you have 5V from pin 18 to pin 9.

    If you have an oscilloscope, check the signal at GS and OSC2, pin 3 and 8 and post the results here.

    What is pin 6 connected to? It should be left open or tied to Gnd.
     
  14. SgtWookie

    Expert

    Jul 17, 2007
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    The outputs have VERY low current source/sink capability. You really need to use transistors or MOSFETs in order to drive your LEDs. The LEDs will be quite dim unless you use driver transistors.

    We do not know where you are, so we don't know what kind of parts you can get. You should put your Country and state or province in your profile. Click on the "User CP" link below the thread title, then click on the "Edit Your Details" link on the left, and then fill the information in under "Location" - then click the "Save changes" button near the bottom.

    For the transistor driver, you will need ~2K resistors from the IC outputs A-D to the bases of general purpose NPN transistors.
    The emitters of the transistors get connected to ground.
    The collectors of the transistors get connected to the cathodes of the LEDs
    The anodes of the LEDs are connected to the 220 Ohm resistors
    The other side of the resistors is connected to +5v.
     
    Last edited: Nov 11, 2011
  15. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    How to find GND from the circuits LM7805
     
  16. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    [​IMG]

    If i use these power supply to my circuit and how to git the ground ( Zero voltage ) from that

    [​IMG]



    thanks for every body
     
  17. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Pin 2 of the 7805 is your ground. You have it connected correctly to your circuit. That's why I wrote it shouldn't be denominated "-5V". Because it isn't.

    Did you check the comments from our previous posts?
     
  18. SgtWookie

    Expert

    Jul 17, 2007
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    In your circuit, "ground" is the 0v reference point. You have to declare some point in your circuit to be 0v/GND, or else it becomes difficult to report measurements.

    If you changed all of your "-5V" notations to "GND", or simply omitted (remove) them where there is a GND symbol, then you would be less confused.
     
  19. eng.altamimi

    Thread Starter New Member

    Nov 1, 2011
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    thanks SgtWookie

    I have this circuit is it working or not?
    [​IMG]



    can i get zero, - 5V and + 5V like this, is it correct point ?
    [​IMG]
     
    Last edited: Nov 13, 2011
  20. SgtWookie

    Expert

    Jul 17, 2007
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    No, that is not what I meant at all.

    This is what I meant for you to do:

    [​IMG]
     
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