Say someone wanted to build a capacitance to voltage converter that could measure say 221pF to 285pF and scale that across a 0-5v output....doable with an Arduino?
Scale that with what resolution? You want 64pF spread over 5V? at 10-bit resolution? 8-bit resolution?
Either way, that's a small capacitance range to be messing with. There's going to be capacitance in your measurement system and microcontroller pins that will reduce accuracy.
How fast do you need to take readings?
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The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected
Find an Elector #4 2011, may be in your local library,
there is an excellent article on measure capacitor with resolution 0.1 pF in range <1 to 2000 pF.
Chip ATtiny2313, but I'm sure there wouldn't be an issue to make it work with arduino.
As high as I can get...10 bit max with the arduino correct?
Readings every 1 second would be fine, even longer if required. Not a super fast application.
RuggedCircuits:
Scale that with what resolution? You want 64pF spread over 5V? at 10-bit resolution? 8-bit resolution?Either way, that's a small capacitance range to be messing with. There's going to be capacitance in your measurement system and microcontroller pins that will reduce accuracy.
How fast do you need to take readings?
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The Rugged Motor Driver: two H-bridges, more power than an L298, fully protected
I'm curious about that Elektor article now.
A simple way to do it is to use the properties of RC circuits and measure the time it takes for a charged capacitor to decay (or an uncharged capacitor to charge). That's the basic circuit. The devil is in the details: leakage currents into the Arduino, repeatability due to variation in the threshold voltage with temperature (and from chip to chip), repeatability due to varying input voltage, etc.
So.....I'm going to say it's doable but it's going to be the type of circuit where the more attention is paid to quality and detail, the better your results will be, and not just by a little bit.
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Beat707: MIDI drum machine / sequencer / groove-box for Arduino
It's true for measuring absolute value.
Author, design hardware with different approach, measure of delta, plus convert C
to frequency by 555.
So if there is a C with well define value (+-1%) and good temperature stability characteristic,
any variation (put some unknown C in parallel) easily to detect.
I have a magazine in pdf, can send in your private e-mail, as copywrong not welcomed on this site.
I found this while looking up information on a capacitive humidity sensor - it might help a bit?
http://starter-kit.nettigo.eu/2010/humidity-sensor/
It uses an RC circuit and tests how long it takes to charge the capacitor, then returns how long it took, which can be converted to capacitance or, in this particular case, humidity.
Looked complicated at first, but once you have it set out, then it's simple!
I would use the timer.
Pass a 1uA (or less) current through the capacitor and measure
the time it takes to reach a specific value. Start the timer
when the capacitor starts charging and stop it
using the analog comparator.
Calculate C using I = C * dv / dt
(* jcl *)