[Tinyos-help] Voltage of AVcc pin on Tmote Sky-Pin1

[Robert Szewczyk]

Voltage reference is a completely different concept than the AVcc.
For the precision of measurements it is the voltage reference
stability that matters.  For information about the stability of the
voltage reference and for the information regarding how to measure the
voltage reference please consult the msp430f1611 datasheet.

Best regards,

Rob

Robert Szewczyk
Moteiv Corporation

On 4/3/07, Michael Schippling <schip at santafe.edu> wrote:
> Unfortunately I don't know anything about the telos devices
> so I can't be much more help there. If it's a fixed regulated
> ref and your sensor is a voltage-divider and runs off the un-reg
> batteries then you'll have difficulties.
>
> As to lowering the ref to get better range at 10mv, I have one
> word: noise. It would be better to amplify the signal with an
> op-amp (the LM324 has a nice down-to-0-rail swing feature) or
> perhaps a simple transistor circuit.
>
> MS
>
> manu suryavansh wrote:
> > Hi,
> > Thanks Michael.
> > I am using the 1.5V reference, I want to know how much does the
> > reference voltage varies. I am planning to use a voltage regulator if it
> > varies much, because Tmote allows to use external reference. As the
> > sensor output is between 0-10mV I am getting very low resolution so
> > either I have to lower the reference or amplify my signal. Usually
> > sensor outputs are low voltage so what is generally done and how a
> > constant supply is maintained?
> > Any suggestions?
> > Thank you
> > Manu Suryavansh
> > UFL
> >
> > */Michael Schippling <schip at santafe.edu>/* wrote:
> >
> >     If the telos is like the mica's the AVcc pin is pretty much the battery
> >     supply, so 2.9v is reasonable. Is there a spec someplace that says it
> >     should be 2.5v?
> >
> >     If the above is true it's actually a feature...yes, a ratio-metric
> >     sensor
> >     is a voltage divider, and the output will change with the supply
> >     voltage.
> >     But (on the mica's at least) the ADC reference voltage is tied to the
> >     battery and droops by the same amount, so they remain (mostly)
> >     calibrated
> >     to each other.
> >
> >     tricky design...do you think it was intentional?
> >     MS
> >
> >     manu suryavansh wrote:
> >      > Hi,
> >      > I measured the voltage of the AVcc pin on tmote sky using a
> >     multimeter
> >      > and it shows to be 2.9 volts. Is it not supposed to be 2.5 volts?- I
> >      > want to use that pin to give supply to my sensor but if that voltage
> >      > keeps varying then output will not be correct because the sensor is
> >      > ratiometric and its output depends on the power supply. Is this the
> >      > correct way to do this?
> >      > Any suggestions will be helpful.
> >      > Thank you
> >      > Manu Suryavansh
> >      > University of Florida
> >      >
> >      > Food fight?
> >      >
> >      > Enjoy some healthy debate
> >      > in the Yahoo! Answers Food & Drink Q&A.
> >      >
> >      >
> >      >
> >      >
> >      >
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