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2007-06-12 by magzky02
The internal ADC of my mega16 is 10 bit. But i want a more accurate one. about 16 bit or better. Anyone can suggest a 16 bit ADC with either SPI or i2c interface. seem some from TI but i want to consideer suggestion first before deciding. the IC should run at 3.3V. regards mago
2007-06-13 by Ralph Hilton
On Wed, 13 Jun 2007 01:50:30 -0000 you wrote: > >The internal ADC of my mega16 is 10 bit. But i want a more accurate >one. about 16 bit or better. Anyone can suggest a 16 bit ADC with >either SPI or i2c interface. seem some from TI but i want to consider >suggestion first before deciding. the IC should run at 3.3V. > >regards >mago Its a bit of a general question. www.ti.com www.analog.com www.linear.com all have parametric search facilities on their websites. I use the LTC2440 24 bit ADC quite a bit. It is easy to set up and has an SPI interface. It is 4.5 volt + but there are slower chips in the LTC24XX range that work on 2.7 volts + . -- Ralph Hilton http://www.ralphhilton.org C-Meter: http://www.cmeter.org FZAOINT http://www.fzaoint.net
2007-06-13 by Roy E. Burrage
Do you really need accuracy or do you actually need resolution? With 16 bits, your least significant bit will be just over 15 microvolts for a 1 volt full scale input. This would equate to 45 microvolts at 2.5 volts FS. At the very least, way down in the mud for most applications. If you use the 10 bit A/D converter of the AVR, which is very linear from my experience, you can get more accurate results with higher resolution by using an averaging filter. There's a good app note for using a moving average filter at the Atmel web site. Don't allow yourself to confuse accuracy with resolution. Unless you're absolutely anal retentive about such things as circuit layout, thermal isolation and compensation, and even solder junction equalization you can bite your own tushi by insisting upon 16 bit accuracy when it isn't necessary. If your LSB is that far down in the mud a gust of cool air from an air conditioner turning on can throw your measurements off. REB magzky02 wrote:
>The internal ADC of my mega16 is 10 bit. But i want a more accurate >one. about 16 bit or better. Anyone can suggest a 16 bit ADC with >either SPI or i2c interface. seem some from TI but i want to consideer >suggestion first before deciding. the IC should run at 3.3V. > >regards >mago > > > >
2007-06-14 by mago Umandam
Yes, what i need ti accuray. Well, i opted higher resolution since the voltage im measuring is of high range 0-80 V. i assume higher resolution will give better accuracy.
regards,
mago
"Roy E. Burrage" <RBurrage@bellsouth.net> wrote:
Do you really need accuracy or do you actually need resolution?
With 16 bits, your least significant bit will be just over 15 microvolts
for a 1 volt full scale input. This would equate to 45 microvolts at
2.5 volts FS. At the very least, way down in the mud for most applications.
If you use the 10 bit A/D converter of the AVR, which is very linear
from my experience, you can get more accurate results with higher
resolution by using an averaging filter. There's a good app note for
using a moving average filter at the Atmel web site.
Don't allow yourself to confuse accuracy with resolution. Unless you're
absolutely anal retentive about such things as circuit layout, thermal
isolation and compensation, and even solder junction equalization you
can bite your own tushi by insisting upon 16 bit accuracy when it isn't
necessary. If your LSB is that far down in the mud a gust of cool air
from an air conditioner turning on can throw your measurements off.
REB
magzky02 wrote:
>The internal ADC of my mega16 is 10 bit. But i want a more accurate
>one. about 16 bit or better. Anyone can suggest a 16 bit ADC with
>either SPI or i2c interface. seem some from TI but i want to consideer
>suggestion first before deciding. the IC should run at 3.3V.
>
>regards
>mago
>
>
>
>
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[Non-text portions of this message have been removed]2007-06-14 by Robert Adsett
At 06:04 PM 6/13/2007 -0700, mago Umandam wrote: >Yes, what i need ti accuray. Well, i opted higher resolution since the >voltage im measuring is of high range 0-80 V. i assume higher resolution >will give better accuracy. Bad assumption. To get higher accuracy you need a lot more than higher resolution. To get 16 bit accuracy you need to get your noise, sensor accuracy, reference voltage and probably power supply stability to better than 1 part in 65536. This is a non trivial exercise. If you can define what you actually need a little better perhaps an easier approach can be suggested. For instance do you really need to cover the full 0-80 or perhaps a subrange? would a log scale work? Robert http://www.aeolusdevelopment.com/ From the Divided by a Common Language File (Edited to protect the guilty) ME - "I'd like to get Price and delivery for connector Part # XXXXX" Dist./Rep - "$X.XX Lead time 37 days" ME - "Anything we can do about lead time? 37 days seems a bit high." Dist./Rep - "that is the lead time given because our stock is live.... we currently have stock."
2007-06-14 by Jim Wagner
doubly bad... Your accuracvy in this situatioh will be dominated by the voltage divider. You will have to pay a lot of money to get 0.1% resistors which is about what you would need to get the accuracy contribution of the divider equal to the accuracy of a 10 bit ADC with perfect reference mid-scale. With a normal "good" reference, the full accuracy gets worse. How much "accuracy" do you need? 1% - 0.1% - 0.001%? And at what sample rate and bandwidth? What are the processing and output requirments? Jim On Wed, 13 Jun 2007 21:20:27 -0400 Robert Adsett <subscriptions@aeolusdevelopment.com> wrote: > At 06:04 PM 6/13/2007 -0700, mago Umandam wrote: > >Yes, what i need ti accuray. Well, i opted higher > resolution since the > >voltage im measuring is of high range 0-80 V. i assume > higher resolution > >will give better accuracy. > > Bad assumption. To get higher accuracy you need a lot > more than higher > resolution. To get 16 bit accuracy you need to get your > noise, sensor > accuracy, reference voltage and probably power supply > stability to better > than 1 part in 65536. This is a non trivial exercise. > > If you can define what you actually need a little better > perhaps an easier > approach can be suggested. For instance do you really > need to cover the > full 0-80 or perhaps a subrange? would a log scale work? > > Robert > > http://www.aeolusdevelopment.com/ > > From the Divided by a Common Language File (Edited to > protect the guilty) > ME - "I'd like to get Price and delivery for connector > Part # XXXXX" > Dist./Rep - "$X.XX Lead time 37 days" > ME - "Anything we can do about lead time? 37 days seems > a bit high." > Dist./Rep - "that is the lead time given because our > stock is live.... we > currently have stock." > --------------------------------------------------------------- The Think Different Store http://www.thinkdifferentstore.com/ For All Your Mac Gear ---------------------------------------------------------------
2007-06-15 by mago Umandam
I am using two ADC's here (current and voltage monitoring). one ADC to measure voltage from 0-70. and another for current from 0-500 mA. For current monitoring, I used a current sense resistor and a precision op amp plus ADC. For the voltage monitoring, i used a voltage divider plus ADC. Sample rate is not critical. i dont mind reading it very slow. I just want to come up with acurate reading specially for the current.
regards
mago
Jim Wagner <jim_d_wagner@applelinks.net> wrote:
doubly bad...
Your accuracvy in this situatioh will be dominated by the
voltage divider. You will have to pay a lot of money to get
0.1% resistors which is about what you would need to get
the accuracy contribution of the divider equal to the
accuracy of a 10 bit ADC with perfect reference mid-scale.
With a normal "good" reference, the full accuracy gets
worse.
How much "accuracy" do you need? 1% - 0.1% - 0.001%?
And at what sample rate and bandwidth? What are the
processing and output requirments?
Jim
On Wed, 13 Jun 2007 21:20:27 -0400
Robert Adsett <subscriptions@aeolusdevelopment.com> wrote:
> At 06:04 PM 6/13/2007 -0700, mago Umandam wrote:
> >Yes, what i need ti accuray. Well, i opted higher
> resolution since the
> >voltage im measuring is of high range 0-80 V. i assume
> higher resolution
> >will give better accuracy.
>
> Bad assumption. To get higher accuracy you need a lot
> more than higher
> resolution. To get 16 bit accuracy you need to get your
> noise, sensor
> accuracy, reference voltage and probably power supply
> stability to better
> than 1 part in 65536. This is a non trivial exercise.
>
> If you can define what you actually need a little better
> perhaps an easier
> approach can be suggested. For instance do you really
> need to cover the
> full 0-80 or perhaps a subrange? would a log scale work?
>
> Robert
>
> http://www.aeolusdevelopment.com/
>
> From the Divided by a Common Language File (Edited to
> protect the guilty)
> ME - "I'd like to get Price and delivery for connector
> Part # XXXXX"
> Dist./Rep - "$X.XX Lead time 37 days"
> ME - "Anything we can do about lead time? 37 days seems
> a bit high."
> Dist./Rep - "that is the lead time given because our
> stock is live.... we
> currently have stock."
>
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