Since I'm working on Tmote Sky (12 bit sampling resolution) I had a look on the relative datasheet at page 23.
It says that Vcc= (sampledData/4096)*Vref*(2R/R) and sampling is done in the middle of 2 equal resistors between the Vcc and ground.
So, from what I could understand Vref (a stable voltage level taken from somewhere) is equals to 1,5V in this case.
So, the sampled value has an accuracy of 1,5/4096=366microvolts...However, when measuring the Vcc this error is doubled since the sampled voltage is relative to just an half of Vcc. Thus, the error rises to 732microvolts, right? This, if Vref ,Vcc are stable and there's no error with sampling.
As the battery get consumed, the Vcc decreases, but Vref should stay stable, isn'tit?
Software components tries to keep Vref constant..Is that you were saying? Then there's some sampling instability
due to some strange effect such as recovery of charges or stuff like that I imagine..that should be the greater source of error I think, since for sampling resolution I would have an error of just 1mV..
Have I misunderstood something...?
--- Gio 1/5/08, Michael Schippling <[EMAIL PROTECTED]> ha scritto:
Da: Michael Schippling <[EMAIL PROTECTED]>
Oggetto: Re: [Tinyos-help] Voltage measurament accuracy
A: "Flavio Pompermaier" <[EMAIL PROTECTED]>
Cc: "[email protected]" <[email protected]>
Data: Giovedì 1 maggio 2008, 01:06
I think the user guides for the various Motes have some information
about the battery voltage measurement. However the Battery components
seem to vary across platforms and TOS versions. I haven't payed much
attention
to them so I can't help with that more. Try searching
this list for battery measurement info.
One rather arcane thing you should know is that, on the mica's
at least, the "battery" measurement made by ADC7 is actually from
a fixed voltage reference chip and the reference value (the max
value you can convert) is the actual battery voltage. So the value
you get RISES as the battery ref drops. I believe the Battery software
components adjust for this, which makes them very hard to understand.
If you're confused about the conversion resolution I gave below
let me know where you got lost and I'll try to make it clearer.
I just guessed at the accuracy based on the fact that the bottom
couple of bits from the onboard converters are usually not very stable.
MS
Flavio Pompermaier wrote:
> thank for the reply. However is there any documentation about this
calculation? I have not well understood the
part regarding the noise and the
conversion to millivolts..
>
> Michael Schippling ha scritto:
>> The ADCs used are either 10 or 12 bits, depending on the controller.
>> That's either 3/1024 volts for the micas or 3/4096 volts for the
tmotes.
>> I think some of the Battery components convert the value to
milli-volts,
>> but there's some noise involved so the actual accuracy is likely
~10 mV.
>> MS
>> Flavio Pompermaier wrote:
>>> Hi to all,
>>> is there anyone that knows the accuracy of batteries voltage
measurement?
>>> Is it in the order of millivolts or microvolts? Or what?
>>>
>>> Best regards,
>>> Flavio
>>>
>>>
>>>
------------------------------------------------------------------------
>>> Tante idee per la salvaguardia del pianeta
su
>>> Yahoo! for good
>>>
<http://us.rd.yahoo.com/mailuk/taglines/isp/control/*http://us.rd.yahoo.com/evt=52436/*http://it.promotions.yahoo.com/forgood/environment.html>.
>>>
>>>
>>>
>>>
------------------------------------------------------------------------
>>>
>>> _______________________________________________
>>> Tinyos-help mailing list
>>> [email protected]
>>>
https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
>> --
>> Platform: WinXP/Cygwin
>> TinyOS version: 1.x, Boomerang
>> Programmer: MIB510
>> Device(s): Mica2, MicaZ, Tmote
>> Sensor board: homebrew
>
>
>
> Tante idee per la salvaguardia del nostro Pianeta su Yahoo! For Good
>
http://it.promotions.yahoo.com/forgood/environment.html
--
Platform: WinXP/Cygwin
TinyOS version: 1.x, Boomerang
Programmer: MIB510
Device(s): Mica2, MicaZ, Tmote
Sensor board: homebrew |
Inviato da Yahoo! Mail.
La casella di posta intelligente.
_______________________________________________
Tinyos-help mailing list
[email protected]
https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
