Rf encoder decoder problem

Discussion in 'The Projects Forum' started by abdom20, Dec 21, 2010.

  1. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    hi guys
    i have problem with my project ....
    i am doing Heart Rate Monitoring System My project have two circuits ...

    1st circuit is to get the heart rate using LED and LDR by placing the finger for 30 second .The signal that we get from the LDR is passed to a microcontroller which is AT89C2051 .Which is programmed to calculate the heart rate and temperature . the temperature is obtained from a IC which is DS1621… this all obtained data should be showed in a LCD (all this is working perfectly for me )

    second circuit should show the same data as the 1st circuit

    To send the data to the second circuit I use a decoder and encoder and a RF module
    The data should be sent from the microcontroller to the decoder to the RF module to the encoder then to the microcontroller (AT89C2051)

    The problem of the project is that iam not getting the data at the second circuit LCD

    I checked all the connection and I did test to the RF module and the encoder and decoder in othe circuit using LED method and it worked fine (means all the componet are ok I think ) the problem is iam not getting data out (no change in voltage) of the encoder to the microcontroller even I tried to connect the encoder and decoder directly but no response

    i measure the voltage of the ports at the microcontroller to checked if there is data out

    At the microcontroller

    Pin 3 : the voltage at 0.27 V when the data is sending the voltage rise 4.14 V then it goes back to 0.27 V

    Pin 11 : the voltage at 0.13 V when the data is sending the voltage rise 4.40 V then it goes back to 0.13 V

    Pin 12: voltage at 0.23 V when the data is sending the voltage rise 4.36 V then it goes back to 0.23 V

    Pin 13: the voltage at 0.21 V when the data is sending the voltage rise 4.36 V then it goes back to 0.21 V

    the votage at the encoder HT12E

    Pin 17 the voltage changing between 1.34V to 1.57V which is the output of the encoder

    AT THE SECOND CIRCUIT

    At the decoder HT12D

    Pin 10 : the voltage is 4.48 V no change when the data is sending as well
    Pin 11: the voltage is 4.48 V no change when the data is sending as well
    Pin 12 : the voltage is 0.10 V no change when the data is sending as well
    Pin 13 : the voltage is 0.10 V no change when the data is sending as well
    Pin 14 the voltage changing between 1.20V to 1.32V which is the output of the encoder

    i think the output from the decoder HT12D is no right so how i overcome this problem ? i appreciate helping me guys
     
    Last edited: Dec 21, 2010
  2. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    Any ideas anyone
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    The output swing from the output of the decoder at pin 14 is much too small at only 1.20V to 1.32V. It must be at least from 1.0V to 3.5V or 0V to 5V. So there is probably something wrong with your radio system.
     
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  4. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    I tried to connect without the rf sys by connecting the pin 17 IN HT12E TO to pin 14 HT12D directly but still having the same problem at the decoder ...
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    The output of the encoder is only 1.6mA which is plenty to drive the "no input current" of the Cmos decoder IC. Its output will swing the entire supply voltage from 0V for a "low" to +5V for a "high".
     
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  6. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    so what do you advice me to do to this circuit ?
     
  7. Audioguru

    New Member

    Dec 20, 2007
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    Use an oscilloscope to see if the output swing of the encoder is correct.
     
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  8. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    sir i already did use an oscilloscope at pin 17 at the encoder and the result was good .. the signal come out when the data sending as low and high .. there is changing but the changing is low as i say the volatage change between 1.34V to 1.57V
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    The output of the encoder driving the Cmos no-current input of the decoder is supposed to be 0V for a low and +5V for a high. Maybe you tested the encoder when its output was overloaded by a high input current requirement of your transmitter.
     
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  10. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    so sir what should i do exactly ? how to overcome this high input current ?
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    Please don't call me a SIR. A SIR is a Knight in your country. I am not a Knight and I am not in your country. Instead call me "Dude" or "Hey You".

    You forgot to post the schematic of your transmitter so we can't see how much input current it needs which might overload the output of the encoder IC.
     
  12. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    "Sir" is also a show of respect for an elder and wiser person, to whom you wish to show good manners and give honor to.

    In ENGLAND they are Knights, elsewhere it's just good manners.

    And that is the whole of it, sir!


    :)
     
  13. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    sorry for that i didn't mean any disrespect for you ..... i attach the circuit again
     
  14. Audioguru

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    Dec 20, 2007
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    Before, I said, "The output swing from the output of the decoder at pin 14 is much too small at only 1.20V to 1.32V. It must be at least from 1.0V to 3.5V or 0V to 5V. So there is probably something wrong with your radio system."

    But you have not posted the schematic of your transmitter so we cannot see if it overloads the output of the encoder.
    You also didn't post the schematic of the receiver so we cannot see if it overloads the output of the decoder and if it has enough gain.
     
  15. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    sorry but i posted the schematics of the both circuit i have for the transmitter circuit and the receiver... i dont know which schematics you mean .
     
  16. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    this is the datasheet for the transmitter
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    The data pin input for the transmitter is shown on its datasheet to be driven from a powerful (25mA) output pin of a microcontroller which you do not have. Instead you are driving the transmitter with a very low power encoder IC that probably cannot drive it (only 1.6mA).

    With an oscilloscope, measure the output swing of the encoder. It should be at least from +0.5V to +4.5V. If there is enough output swing then post the datasheet for the receiver.
     
  18. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    i got the oscilloscope output for the transmitter and the receiver .. the output voltage for both transmitter and receiver are swinging from 0-5v
    i couldnt see this one on the multimeter because the changing is so fast
     
  19. Audioguru

    New Member

    Dec 20, 2007
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    Good!
    The decoder does not work properly because there is no data, just a square-wave.
    Maybe the micro-controller sends only a carrier without any data modulating it.
     
  20. abdom20

    Thread Starter New Member

    Aug 12, 2010
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    u mean there is no data sent from the transmitter or there is no data received? what is the problem ? because i have changed the decoder but still same response.
     
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