DAC0832 and LM324

Discussion in 'Embedded Systems and Microcontrollers' started by zoozd, Apr 3, 2013.

  1. zoozd

    Thread Starter New Member

    Apr 3, 2013
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    Hello,

    I am using DAC0832 (National Instruments) to convert from digital to analog in order to fade in and out two LEDs in parallel.

    All the active low inputs XFER, WR2, CS, are connected to ground, and ILE is connected to +5V logic input. Vcc and Vref are also +5V input from the microcontroller (HCS12DT).

    The data is sent through port A of the microcontroller.

    Iout1 is inputted to the non-inverting input of LM324, and the inverting input is set to GND. R feedback is connected to the output of LM324 and the output is supposedly to be connected to the LEDs. Vcc+ of the LM324 is 7V and Vcc- is GND.

    Iout2 is grounded. AGND and GND are GND.

    If the +5V power was off, and the microcontroller wasn't even connected, I would get 5.9V out of the output of LM324. When it is connected and power is on, guess what I get? 5.9V. If I latch digital input of zero I get 5.9V, if I latch 0xFF, I get 5.9 V. (Values may slightly change +-0.02V).

    I'm pretty sure that the op-amp is working because I tried it over other devices and I got a range of readings from 0 up to something around 6 Volts.

    What is going on?
     
  2. Markd77

    Senior Member

    Sep 7, 2009
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  3. MrChips

    Moderator

    Oct 2, 2009
    12,435
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    Look over the DAC0830/0832 data sheet.
    Iout1 goes to the inverting input.
    Iout2 goes to the non-inverting input.
    The output is inverted from the VREF input.
     
  4. zoozd

    Thread Starter New Member

    Apr 3, 2013
    7
    0
    Iout2 goes to ground, and so does the inverting input in my configuration. I tried also connecting Iout1 to the inverting input and grounding the non-inverting one. Same results.

    Yes i'm trying to use it as a buffer.
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    The op amp is not a buffer. It is a current to voltage converter.
    You need to use a bipolar power supply. A positive VREF will produce a negative output.

    A simpler DAC to use is a AD558.
     
  6. zoozd

    Thread Starter New Member

    Apr 3, 2013
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    I'm sorry, you are right, it is a current to voltage converted that boosts up my current.

    I can't use a bipolar power supply as I can't have negative voltages. That is why I used the only single supply op-amp that I could find (which is a quad one).

    Maybe I'll try to find that DAC.
     
  7. zoozd

    Thread Starter New Member

    Apr 3, 2013
    7
    0
    Thank you all, I was able to use a single supply op amp with DAC0832 in a configuration that outputs voltage. This configuration is in the datasheet of the DAC.
     
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