Capacitance Meter
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Posts: 46,084
Hi there:
Does anyone have a schematic and program to build one of these items around a
BS2?
If so please let me know as I am interested in building one of these goodies.
For a display, I could make it really simple by making a pin into an output
which would then go into a D/A converter (or I can use the PWM command for that
pin) and just using a preconfigured digital display or even a needle movement
voltmeter to give me a voltage display that would correspond to the capacitance.
I am not looking for nuclear grade accuracy but I would like to see good
repeatability; that will allow me to use the program to fine tune the system and
then calibrate using a computer interface.
Thanks in advance.
Gerry Shand
gerry_shand@t...
Does anyone have a schematic and program to build one of these items around a
BS2?
If so please let me know as I am interested in building one of these goodies.
For a display, I could make it really simple by making a pin into an output
which would then go into a D/A converter (or I can use the PWM command for that
pin) and just using a preconfigured digital display or even a needle movement
voltmeter to give me a voltage display that would correspond to the capacitance.
I am not looking for nuclear grade accuracy but I would like to see good
repeatability; that will allow me to use the program to fine tune the system and
then calibrate using a computer interface.
Thanks in advance.
Gerry Shand
gerry_shand@t...
Comments
>
> Hi there:
>
> Does anyone have a schematic and program to build one of these items
> around a BS2?
>
> If so please let me know as I am interested in building one of these
> goodies. For a display, I could make it really simple by making a pin into
> an output which would then go into a D/A converter (or I can use the PWM
> command for that pin) and just using a preconfigured digital display or
> even a needle movement voltmeter to give me a voltage display that would
> correspond to the capacitance. I am not looking for nuclear grade accuracy
> but I would like to see good repeatability; that will allow me to use the
> program to fine tune the system and then calibrate using a computer
> interface.
>
The Stamp Manual has all the info you need. The RCtime
command can be used to do just what you're looking for. The trick
is to make several 'ranges' (by using several pins) each with an
appropriately-sized *precision* i.e. 1% tolerance resistor. That
should make a handy little meter.
Mark Hillier, VE6HVW
President, HVW Technologies Inc.
Canadian Distributors of Parallax Products and other Neat Stuff
Tel: +403-730-8603 Fax: +403-730-8903
http://www.hvwtech.com
Stamps (http://www.al-williams.com/awce/sbook.htm). The interesting twist,
if I recall, is that not only does it measure capacitance, but it outputs a
voltage so you can read the result with the DVM.
Remember that RCTime is proportional to the RC constant. So while you
usually vary the R, you can just as well vary the C. Given that, a simple
cap meter might be an RCTime statement, some math to do the calculations,
and a debug statement.
Regards,
Al Williams
AWC
* Control 8 servos: http://www.al-williams.com/awce/pak8.htm
>
Original Message
> From: gerry_shand@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=JtcDFMVP1mFg4ZgbvC4yuI9lmjTxJXevY_3cK95DIQ1EfobefB-mniAMlt3hs8u400SmtN0hEK9-OSQUYEEc]gerry_shand@t...[/url
> Sent: Friday, September 29, 2000 3:14 PM
> To: basicstamps@egroups.com
> Subject: [noparse][[/noparse]basicstamps] Capacitance Meter
>
>
>
>
> Hi there:
>
> Does anyone have a schematic and program to build one of these
> items around a
> BS2?
>
> If so please let me know as I am interested in building one of
> these goodies.
> For a display, I could make it really simple by making a pin into
> an output
> which would then go into a D/A converter (or I can use the PWM
> command for that
> pin) and just using a preconfigured digital display or even a
> needle movement
> voltmeter to give me a voltage display that would correspond to
> the capacitance.
> I am not looking for nuclear grade accuracy but I would like to see good
> repeatability; that will allow me to use the program to fine tune
> the system and
> then calibrate using a computer interface.
>
> Thanks in advance.
>
> Gerry Shand
> gerry_shand@t...
>
>
>
>
> From: gerry_shand@t...
Check the RCtime command and then use integrated PWM output
or a PULSOUT after calculating C from the RCTIME using
appropriate resistance for "R" - for wider range you could
add a feature to switch "R"s electronically.
Another possibility is to use a 555 RC oscillator and then
PULSIN to derive C. And there are many more possibilities :-)
Depends some on what values you are trying to measure.
________________________________________________________________
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and not the stamp II I never could figure out the conversions,and never got
the program to work on a stamp II
At 03:28 PM 9/29/2000 -0500, you wrote:
>The plans for a cap meter appear in Microcontroller Projects with Basic
>Stamps (http://www.al-williams.com/awce/sbook.htm). The interesting twist,
>if I recall, is that not only does it measure capacitance, but it outputs a
>voltage so you can read the result with the DVM.
>
>Remember that RCTime is proportional to the RC constant. So while you
>usually vary the R, you can just as well vary the C. Given that, a simple
>cap meter might be an RCTime statement, some math to do the calculations,
>and a debug statement.
>
>
>Regards,
>
>
>Al Williams
>AWC
>* Control 8 servos: http://www.al-williams.com/awce/pak8.htm
>
>
>>
Original Message
>> From: gerry_shand@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=HJzD8tbyugBUfUQJtfviByZaDPeo9OfqVNLqvxk-2U1cpNNWJj7roIHkD4kS1jttyNwvNVdJ6TG0Tga84LU]gerry_shand@t...[/url
>> Sent: Friday, September 29, 2000 3:14 PM
>> To: basicstamps@egroups.com
>> Subject: [noparse][[/noparse]basicstamps] Capacitance Meter
>>
>>
>>
>>
>> Hi there:
>>
>> Does anyone have a schematic and program to build one of these
>> items around a
>> BS2?
>>
>> If so please let me know as I am interested in building one of
>> these goodies.
>> For a display, I could make it really simple by making a pin into
>> an output
>> which would then go into a D/A converter (or I can use the PWM
>> command for that
>> pin) and just using a preconfigured digital display or even a
>> needle movement
>> voltmeter to give me a voltage display that would correspond to
>> the capacitance.
>> I am not looking for nuclear grade accuracy but I would like to see good
>> repeatability; that will allow me to use the program to fine tune
>> the system and
>> then calibrate using a computer interface.
>>
>> Thanks in advance.
>>
>> Gerry Shand
>> gerry_shand@t...
>>
>>
>>
>>
>
>
>
>
>
Sincerely
Kerry
Admin@M...
WWW server hosting
[url=Http://mntnweb.com]Http://mntnweb.com[/url]
Binghamton online Webcam [url=Http://MntnWeb.Com/bing.htm]Http://MntnWeb.Com/bing.htm[/url]
CHRISTMAS Web Page [url=Http://mntnweb.com/xmas.htm]Http://mntnweb.com/xmas.htm[/url]
--So you think you need more memory... the LEM went to the moon on 16K,how
much do you REALLY need?
book and it uses RCTIME -- a Stamp II command (the I uses POT instead).
The program uses Gausfit to calculate a polynomial to convert counts to uF.
Of course, the resulting polynomial was:
.0000008*x**3 - .0005262967*x**2 + .5838454*x + .4225229
This takes some trickery to calculate on the Stamp (and no, I didn't use a
PAK I or II although that certainly would be one option).
There is probably a Stamp I version floating around somewhere else (maybe an
old SOM project or something).
Regards,
Al Williams
AWC
* Control 8 servos at once! http://www.al-williams.com/awce/pak8.htm
>
Original Message
> From: Kerry Barlow [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=dhCSdiVLL2ZBS31UMPQ4sMDs__pIewD0boBHGylYKppS9p_EZ3AHV0EBOBRS6BLFxOI1zg4QfGjmTgvN]admin@m...[/url
> Sent: Saturday, September 30, 2000 10:50 AM
> To: basicstamps@egroups.com
> Subject: RE: [noparse][[/noparse]basicstamps] Capacitance Meter
>
>
> I have seen that stamp article also however it is designed for the stamp 1
> and not the stamp II I never could figure out the conversions,and
> never got
> the program to work on a stamp II
>
>
>
> At 03:28 PM 9/29/2000 -0500, you wrote:
> >The plans for a cap meter appear in Microcontroller Projects with Basic
> >Stamps (http://www.al-williams.com/awce/sbook.htm). The
> interesting twist,
> >if I recall, is that not only does it measure capacitance, but
> it outputs a
> >voltage so you can read the result with the DVM.
> >
> >Remember that RCTime is proportional to the RC constant. So while you
> >usually vary the R, you can just as well vary the C. Given that, a simple
> >cap meter might be an RCTime statement, some math to do the calculations,
> >and a debug statement.
> >
> >
> >Regards,
> >
> >
> >Al Williams
> >AWC
> >* Control 8 servos: http://www.al-williams.com/awce/pak8.htm
> >
> >
> >>
Original Message
> >> From: gerry_shand@t... [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=-aE2mUeqLVJ3ThVsBCILAOoM7xtVF-cyi0kZRX6IaND5oG_3lx-euKbdiZOa6sm72DCfDsOH7Kaw1AsX8N0]gerry_shand@t...[/url
> >> Sent: Friday, September 29, 2000 3:14 PM
> >> To: basicstamps@egroups.com
> >> Subject: [noparse][[/noparse]basicstamps] Capacitance Meter
> >>
> >>
> >>
> >>
> >> Hi there:
> >>
> >> Does anyone have a schematic and program to build one of these
> >> items around a
> >> BS2?
> >>
> >> If so please let me know as I am interested in building one of
> >> these goodies.
> >> For a display, I could make it really simple by making a pin into
> >> an output
> >> which would then go into a D/A converter (or I can use the PWM
> >> command for that
> >> pin) and just using a preconfigured digital display or even a
> >> needle movement
> >> voltmeter to give me a voltage display that would correspond to
> >> the capacitance.
> >> I am not looking for nuclear grade accuracy but I would like
> to see good
> >> repeatability; that will allow me to use the program to fine tune
> >> the system and
> >> then calibrate using a computer interface.
> >>
> >> Thanks in advance.
> >>
> >> Gerry Shand
> >> gerry_shand@t...
> >>
> >>
> >>
> >>
> >
> >
> >
> >
> >
> Sincerely
> Kerry
> Admin@M...
> WWW server hosting
> [url=Http://mntnweb.com]Http://mntnweb.com[/url]
> Binghamton online Webcam [url=Http://MntnWeb.Com/bing.htm]Http://MntnWeb.Com/bing.htm[/url]
> CHRISTMAS Web Page [url=Http://mntnweb.com/xmas.htm]Http://mntnweb.com/xmas.htm[/url]
> --So you think you need more memory... the LEM went to the moon
> on 16K,how
> much do you REALLY need?
>
>
>
>
>
uF.
>Of course, the resulting polynomial was:
>
>.0000008*x**3 - .0005262967*x**2 + .5838454*x + .4225229
>
>This takes some trickery to calculate on the Stamp (and no, I didn't use a
>PAK I or II although that certainly would be one option).
How come it needs gausfit? The formula is BASICally
C=constant/R.
Determining the constant takes o one-point calibration to account for the
threshold of the Stamp and the tolerance of the resistor.
Al, they had your "BASIC Stamps" book on display at the Embedded systems
conference in San Jose CA last week, at the CMP Books booth. Good book! I
also found an interesting new book there, "MATH Toolkit for REAL-TIME
Programming" - Do big math on small machines. by Jack Crenshaw, a
compilation of columns he has written for "Embedded Systems"magazine
through the years.
-- Tracy Allen
electronically monitored ecosystems
http://www.emesystems.com
"There is nothing quite so practical as a good theory" -- Williard Gibbs.
can see the higher-order coefficients are very low, so ignoring them doesn't
make much difference. In practice, stray capacitance and other effects don't
make the fit exact, and -- as you know -- not everything has that sort of
easy fit.
Glad you liked the book.
Regards,
Al Williams
AWC
*Floating point math for the Stamp, PIC, SX, or any microcontroller at
http://www.al-williams.com/awce/pak1.htm