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Sigma Delta with the Prop — Parallax Forums

Sigma Delta with the Prop

James LongJames Long Posts: 1,181
edited 2008-02-28 19:02 in Propeller 1
I'm going to ask.....and if this is not in the correct forum, please move it.


How does the Propeller do analog to digital conversion using sigma delta?

I know nothing about sigma delta ADC's so.....the method alludes me.

I'm asking, because I need to sense a threshold of voltage, and would like to not use an ADC if possible. I just don't want to add another chip to the board.

Any help would be greatly appreciated,

James L

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James L

Partner/Designer
Lil Brother LLC (SMT Assembly Services)

Comments

  • RaymanRayman Posts: 14,162
    edited 2008-02-28 18:26
    I've got some info here:

    http://www.rayslogic.com/propeller/Programming/ADC.htm
  • James LongJames Long Posts: 1,181
    edited 2008-02-28 18:41
    Rayman (Chip or anyone else)

    Couldn't I just build a voltage divider and use the input threashold of the Propeller for a detector?

    This would be much simpler than the Sig Delt ADC....althought I like the idea of the Sig Delt.

    How accurate is the threshold level of the propeller pins?

    James L

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    James L

    Partner/Designer
    Lil Brother LLC (SMT Assembly Services)
  • Graham StablerGraham Stabler Posts: 2,507
    edited 2008-02-28 18:52
    Yes you could and if it isn't a good enough threshold add a comparitor
  • cgraceycgracey Posts: 14,133
    edited 2008-02-28 18:57
    The threshold level is VDD/2 by design, but this level varies with·manufacturing process, operating voltage, and temperature. I would estimate that the level could·vary from VDD/2 by +/-25%. As long as temperature and voltage are steady (whereas process variation is set at manufacturing time), the threshold level will be constant, with perhaps several millivolts of hysteresis.

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    Chip Gracey
    Parallax, Inc.
  • James LongJames Long Posts: 1,181
    edited 2008-02-28 19:02
    Maybe I'll stick with the Sigma Delta for now.

    I haven't ever played with one....so there is going to be a revision I'm sure.

    I think it has better chance of success, plus I already have the program (in the counters application) so implementation will be pretty easy.

    I'll have to figure out what I need to get the voltage to the correct level, but Rayman's website can help there a lot.

    James L

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    James L

    Partner/Designer
    Lil Brother LLC (SMT Assembly Services)
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