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ADC question

JavalinJavalin Posts: 892
edited 2005-07-26 16:49 in General Discussion
hello chaps,

Can you use an ADC chip i.e. the ADC0831/2 (http://www.national.com/pf/AD/ADC0831.html)

to monitor a 12V battery as part of rover power monitor system?

Are there any issues with ground loops, possibilty to blow up my stamp?

Any other/better ways of doing it?

Cheers

james

Comments

  • KenMKenM Posts: 657
    edited 2005-07-25 15:01
    I did not read the spec sheet of the ADC you are considering, but there should not be any major issues.

    Also, there are other ways of doing it.

    What stamp do you have?

    If you are concerned only with knowing when the battery voltage drope below a certain level, there a alternatives to using an ADC with less parts.

    The higher end stamp, BS2px has a comparitor function, it will compare the voltage on one pin verses another pin.

    Another quick and dirty method is to feed a voltage divider from your battery.

    Feed that output of the divider to a stamp input pin.

    The voltage divider resistors would be chosen so that the low battery voltage level is 1.4 volts. Then you can sense a logic 0 or logic 1 to know if you are above or below your "low voltage" trip point.

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    Ken
  • JavalinJavalin Posts: 892
    edited 2005-07-25 15:42
    Hi KenM,

    Thanks for the response. I'm using a Javalin Stamp.

    As I probably will want to measure several power lines, I think i'll go with the ADC route.

    There are some IC's arround that seem to do this and output via the 1-wire bus. However these seem difficult to get hold of!! And there in SMT formats for board mounting..... And difficult to use!

    Cheers

    james
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-25 17:08
    James,

    ·· Bear in mind that a resistor divider will be needed even if you do use the ADC, since it's input can only handle 5V max.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • JavalinJavalin Posts: 892
    edited 2005-07-25 18:36
    Hi Chris,

    Doesn't the ADC reference the input voltage against its supply (ref) voltage? i.e. if you supply 12V and measure 6V you'll get half.

    ???

    James
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2005-07-26 03:42
    James,

    ·· I suppose ideally that would be the case.· But in your case you're trying to measure a 12V signal.· The ADC0831 is rated at only 5VDC.· The VRef cannot be larger than the Supply Voltage.· Therefore you will need to divide down your input voltage to within acceptable range of the ADC chip you're using.

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    Chris Savage
    Parallax Tech Support
    csavage@parallax.com
  • JavalinJavalin Posts: 892
    edited 2005-07-26 16:49
    Hi Chris,

    oh. Ok thanks for the help!

    James
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