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transducer to BS2

TobiasTobias Posts: 95
edited 2007-07-07 15:58 in BASIC Stamp
What is the most accurate way to tell my BS2 what my 1-6 volt 0-150psi transducer's output· I am going through a rctime curcuit but I am getting inaccurate values what is your advise? Thank-You Toby

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-07 05:13
    The most accurate way is to use an external analog to digital converter like the ADC0831. Download the Basic Analog and Digital tutorial from the Stamps in Class sections of the Parallax website for information on using this and similar devices.
  • TobiasTobias Posts: 95
    edited 2007-07-07 05:37
    I don't know if you've every heard of a picaxe but that has an ad converter built in, there still appears to be a curve in my values so is this going to happen to the external ad converter for the basic stamp?
  • Mike GreenMike Green Posts: 23,101
    edited 2007-07-07 05:51
    Yes, the PicAxe is another PIC-based competitor for the Stamps that has a built-in ADC. I suspect the curve you're seeing may be an artifact of the sensor so you may see the same curve with an external ADC on a Stamp. By the way, if your sensor has a 1-6V output, you'll need to reduce that for use with an ADC to a 0-5V range. A simple resistor voltage divider should work fine.
  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2007-07-07 05:55
    Tobias,

    "there still appears to be a curve in my values..."

    Is it possible that your sensor does not have a linear response? Some sensors of this nature can have an exponential output in which case you would see a curve. Compound this with using
    the RCTIME function which is also exponential (<- due to the charge/discharge curve on the capacitor) and you can have interesting results.

    Mike is correct however, the most accurate method will be to use an external analog to digital converter. We have a few ADC's to choose from if you decide to go that route.

    www.parallax.com/detail.asp?product_id=ADC0831
    www.parallax.com/detail.asp?product_id=604-00027
    www.parallax.com/detail.asp?product_id=604-00001
    www.parallax.com/detail.asp?product_id=604-00026

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • TobiasTobias Posts: 95
    edited 2007-07-07 14:50
    Quick question, I built ten idenical boards with the same value in components for the rctime curcuit and all the other curcuits and not one board show the same value they can differ up the 10 different values?
  • allanlane5allanlane5 Posts: 3,815
    edited 2007-07-07 15:58
    Yup, every device can need a different linearization curve -- depending on the level of precision you need.
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