Problem with ADC0808CCN

Discussion in 'Homework Help' started by arivalagan13, Feb 21, 2010.

  1. arivalagan13

    Thread Starter Member

    Apr 30, 2009
    29
    0
    Hi group..
    I hope everyone is doing well..
    I got a problem with ADC circuit..
    Before my problem kindly have a look at the circuit I used to test the ADC with attachments..
    I'm using ADC0808CCN,which is a 8-channel ADC..
    I need to use 4(out of 8) channels for my application..

    Before doing that I decided to test one channel by the manner shown in the circuit diagram that I attached..

    But the conversion is not taking place...

    I'm getting strange responses...which I can't even explain
    I used 640kHz clock(also tried with 550kHz)..

    I'm getting the same response with and without the clock..

    Kindly help me to sort out this problem..



    Thanks & Regards,
    Arivu
     
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  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The ALE pin requires only a pulse and not a continuous 5V signal. Use a pushbutton to pulse it once. Also, you need resistors in series with each diode to limit the current.
     
  3. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    The converter is intended to communicate with a microprocessor, not drive LED's directly. You need to place a 300 ohm resistor in series with each LED to keep high currents from destroying the internal circuitry.
     
  4. arivalagan13

    Thread Starter Member

    Apr 30, 2009
    29
    0
    I tried the circuit with pulse(instead 0f +Vcc) to ALE...also with resistors in series with LEDs...but still I'm getting the same response...


    Also,suggest me(with IC numbers) some popular 4-channel ADC with 8- to 12-bit resolution...and a single channel ADC with the same resolution..


    Regards & Thanks,
    Arivu
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    What response are you getting?
     
  6. arivalagan13

    Thread Starter Member

    Apr 30, 2009
    29
    0
    when I connect the circuit all the LEDs are glowing(but across some LEDs I'm getting about 3.2V and 2.16V across some LEDs)..

    Also I'm getting the same response(as I said above) with or without clock signal)..





    Arivu
     
  7. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The voltage across the leds shouldn't be exactly the same.

    How are you pulsing the ALE pin?
     
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