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

2007-04-03 Thread 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 <[EMAIL PROTECTED]> 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 <[EMAIL PROTECTED]>/* 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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>  >
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>
>
> 
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Re: [Tinyos-help] Voltage of AVcc pin on Tmote Sky-Pin1

2007-04-03 Thread 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 <[EMAIL PROTECTED]>/* 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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 > Tinyos-help mailing list
 > Tinyos-help@Millennium.Berkeley.EDU
 >
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Re: [Tinyos-help] Voltage of AVcc pin on Tmote Sky-Pin1

2007-04-03 Thread manu suryavansh 
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 <[EMAIL PROTECTED]> 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. 
>  
> 
> 
> 
> 
> 
> ___
> Tinyos-help mailing list
> Tinyos-help@Millennium.Berkeley.EDU
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[Fwd: [Tinyos-help] Voltage of AVcc pin on Tmote Sky-Pin1]

2007-04-03 Thread Benjamin Madore 


- Original Message -
Subject: [Tinyos-help] Voltage of AVcc pin on Tmote Sky-Pin1
From:"manu suryavansh" <[EMAIL PROTECTED]>
Date:Tue, March 27, 2007 4:34 pm
To:  "moteiv" <[EMAIL PROTECTED]>


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



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-- 
The difference between the right word and the almost right word is really a
large matter- it's the difference between a lightning bug and the lightning.
-TwainHi,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 youManu SuryavanshUniversity of Florida 

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

2007-04-03 Thread manu suryavansh 
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


 
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