From: <chr...@gm...> - 2010-12-03 22:07:53
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Hey all. I'm a humble grad student doing some device engineering; we're considering the Gumstix platform. It's really impressive how many accessories and features are available for this system, to say nothing of the community that's sprung up around it. My system needs to detect a voltage from a biomed sensor about once a second, record it to a file, present a UI to a single user that's physically present, and be fairly insensitive to mechanical shock. All of these are standard problems with standard solutions available for the Googling - except for the sensor. It takes 6VDC and outputs a voltage to the tune of 5 uV/V/mmHg, eg for a supply voltage of 6V and a pressure of 100mmHg, it should output about 3mV, plus some offset. Obviously, the standard ADC as shipped is too coarse for this application, which gives rise to the following questions: 1) How practical is it to modify the ADC's reference voltages? Googling reveals that they're apparently pinned to ground and V_acc; can I change V_acc without disturbing other functionality on the board? How hard is it to disconnect these two pins from the factory circuitry and supply my own voltages, perhaps from onboard DACs? 2) What's the ADC's behavior in edge cases? As in, if I set the reference voltages 1mV apart, will it give me uV sensitivity with 10 bits of resolution? Any ideas, discussion, useful abuse etc are appreciated. Thanks, Chris -- View this message in context: http://old.nabble.com/ADC-usability-in-highly-precise-applications--tp30366574p30366574.html Sent from the Gumstix mailing list archive at Nabble.com. |
From: <de...@gm...> - 2010-12-03 22:24:15
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Why not put an amplifier on the Analog signal and scale its output? Your question seems to be missing a few parameters ( unless I miss read it). 1) what is the signal type differential or single ended? 2) is the voltage range correlating from 0 to max pressure? 3) what are your repeatability and accuracy requirements? Depending on the answer to this will tell us if you need 10, 12, 14, 16 or 24 bit ADC. My guess is that 12 or 16 bit will be sufficient. The next question is whether the operating temperature varies enough to require temperature compensation on the sensor and circuitry (again depends on your requirements). Hope this helps Nate On Dec 3, 2010, at 17:07, "chr...@gm..." <chr...@gm...> wrote: > > Hey all. > > I'm a humble grad student doing some device engineering; we're considering > the Gumstix platform. It's really impressive how many accessories and > features are available for this system, to say nothing of the community > that's sprung up around it. > > My system needs to detect a voltage from a biomed sensor about once a > second, record it to a file, present a UI to a single user that's physically > present, and be fairly insensitive to mechanical shock. All of these are > standard problems with standard solutions available for the Googling - > except for the sensor. > > It takes 6VDC and outputs a voltage to the tune of 5 uV/V/mmHg, eg for a > supply voltage of 6V and a pressure of 100mmHg, it should output about 3mV, > plus some offset. Obviously, the standard ADC as shipped is too coarse for > this application, which gives rise to the following questions: > > 1) How practical is it to modify the ADC's reference voltages? Googling > reveals that they're apparently pinned to ground and V_acc; can I change > V_acc without disturbing other functionality on the board? How hard is it to > disconnect these two pins from the factory circuitry and supply my own > voltages, perhaps from onboard DACs? > 2) What's the ADC's behavior in edge cases? As in, if I set the reference > voltages 1mV apart, will it give me uV sensitivity with 10 bits of > resolution? > > Any ideas, discussion, useful abuse etc are appreciated. > > Thanks, > Chris > -- > View this message in context: http://old.nabble.com/ADC-usability-in-highly-precise-applications--tp30366574p30366574.html > Sent from the Gumstix mailing list archive at Nabble.com. > > > ------------------------------------------------------------------------------ > Oracle to DB2 Conversion Guide: New IBM DB2 features make compatibility easy. > Learn about native support for PL/SQL, new data types, scalar functions, > improved concurrency, built-in packages, OCI, SQL*Plus, data movement tools, > best practices and more - all designed to run applications on both DB2 and > Oracle platforms. http://p.sf.net/sfu/oracle-sfdev2dev > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users |
From: <chr...@gm...> - 2010-12-04 21:13:14
|
Hey, thanks for the prompt reply! Part of my problem is my unfamiliarity with the Gumstix platform, so I'm not sure how to scale my signal. Do the gumstix ADCs read from 0 to 5V? From 0 to 1.8? How hard would it be to change their reference voltages? Sent from my BlackBerry device from Cincinnati Bell Wireless -----Original Message----- From: "de...@gm..." <de...@gm...> Date: Fri, 3 Dec 2010 17:23:04 To: General mailing list for gumstix users.<gum...@li...> Reply-To: "General mailing list for gumstix users." <gum...@li...> Subject: Re: [Gumstix-users] ADC usability in highly precise applications? Why not put an amplifier on the Analog signal and scale its output? Your question seems to be missing a few parameters ( unless I miss read it). 1) what is the signal type differential or single ended? 2) is the voltage range correlating from 0 to max pressure? 3) what are your repeatability and accuracy requirements? Depending on the answer to this will tell us if you need 10, 12, 14, 16 or 24 bit ADC. My guess is that 12 or 16 bit will be sufficient. The next question is whether the operating temperature varies enough to require temperature compensation on the sensor and circuitry (again depends on your requirements). Hope this helps Nate On Dec 3, 2010, at 17:07, "chr...@gm..." <chr...@gm...> wrote: > > Hey all. > > I'm a humble grad student doing some device engineering; we're considering > the Gumstix platform. It's really impressive how many accessories and > features are available for this system, to say nothing of the community > that's sprung up around it. > > My system needs to detect a voltage from a biomed sensor about once a > second, record it to a file, present a UI to a single user that's physically > present, and be fairly insensitive to mechanical shock. All of these are > standard problems with standard solutions available for the Googling - > except for the sensor. > > It takes 6VDC and outputs a voltage to the tune of 5 uV/V/mmHg, eg for a > supply voltage of 6V and a pressure of 100mmHg, it should output about 3mV, > plus some offset. Obviously, the standard ADC as shipped is too coarse for > this application, which gives rise to the following questions: > > 1) How practical is it to modify the ADC's reference voltages? Googling > reveals that they're apparently pinned to ground and V_acc; can I change > V_acc without disturbing other functionality on the board? How hard is it to > disconnect these two pins from the factory circuitry and supply my own > voltages, perhaps from onboard DACs? > 2) What's the ADC's behavior in edge cases? As in, if I set the reference > voltages 1mV apart, will it give me uV sensitivity with 10 bits of > resolution? > > Any ideas, discussion, useful abuse etc are appreciated. > > Thanks, > Chris > -- > View this message in context: http://old.nabble.com/ADC-usability-in-highly-precise-applications--tp30366574p30366574.html > Sent from the Gumstix mailing list archive at Nabble.com. > > > ------------------------------------------------------------------------------ > Oracle to DB2 Conversion Guide: New IBM DB2 features make compatibility easy. > Learn about native support for PL/SQL, new data types, scalar functions, > improved concurrency, built-in packages, OCI, SQL*Plus, data movement tools, > best practices and more - all designed to run applications on both DB2 and > Oracle platforms. http://p.sf.net/sfu/oracle-sfdev2dev > _______________________________________________ > gumstix-users mailing list > gum...@li... > https://lists.sourceforge.net/lists/listinfo/gumstix-users ------------------------------------------------------------------------------ Oracle to DB2 Conversion Guide: New IBM DB2 features make compatibility easy. Learn about native support for PL/SQL, new data types, scalar functions, improved concurrency, built-in packages, OCI, SQL*Plus, data movement tools, best practices and more - all designed to run applications on both DB2 and Oracle platforms. http://p.sf.net/sfu/oracle-sfdev2dev _______________________________________________ gumstix-users mailing list gum...@li... https://lists.sourceforge.net/lists/listinfo/gumstix-users |