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

[Michael Schippling]

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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