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Capacitance Measurement
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Please be positive and constructive with your questions and comments.

by guess_who! on Fri Apr 13, 2007 7:15 pm

ladyada wrote:
mikewitt wrote:The board is here:
http://witt.michael.googlepages.com/555Capacitance2.brd

It's small enough that it should fit nicely behind the LCD I use, so you could have a relatively small hand held capacitance meter. You could probably even put it in the form of a set of tweezers.

After getting the specs for it, it looks like it'll cost people $5 for JUST THE PCB (plus shipping, PM for actual costs). It would be another ~5-10 for components (no lcd, shipping extra) and if I get at least ten people, it will be ~$22.46 (up to a dollar or two extra, cover s/h costs from SparkFun) each (before shipping).


Your timing is impeccable, or at least you reminded me to get off my ass and start working on this project again...woooo

http://www.ladyada.net/wiki/doku.php?id ... h:lcrmeter

"Handheld, battery powered device for determining impedance of inductors, capacitors and resistors"
Maybe you should change the wording, because someone might not realize that impedance refers to the measurements of all three kinds of components.
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by adafruit on Fri Apr 13, 2007 7:39 pm

sure, its also a wiki so feel free to edit it yourself :)

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by guess_who! on Sat Apr 14, 2007 11:57 pm

Handheld, battery powered device for determining impedance of inductors (inductance), capacitors (capacitance) and resistors (resistance)

May also measure other things like inductor Q, capacitor leakage, series resistance, etc.
------------------------------
Handheld, battery powered device for determining impedance of the following types of components: inductors (inductance), capacitors (capacitance) and resistors (resistance)

May also measure other things like inductor Q, capacitor leakage, equivalent series resistance, etc.
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by adafruit on Sun Apr 15, 2007 12:05 am

fixed the ESR/DCR thing

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by guess_who! on Sun Apr 15, 2007 12:51 am

I still think that you should change the first part, to make it clearer.
I had trouble with the wiki. Should I message you stuff to change, or post it in the forum?
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by druidi on Wed Apr 18, 2007 4:47 pm

can i replace tiny2313 by atmega8 ? I'm a total noob with those microcontrollers...
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by mikewitt on Wed Apr 18, 2007 6:09 pm

You can, but you'll have to modify the schematics as well as the makefile.

Right now, I'm working on getting my digital pots to work, but after I get that, I might be able to help some more. The way I learned was by building the MiniPOV, and examining the code and the spec sheets for the AVRs. I eventually built a working knowledge of the devices, and built this. I would recommend that path if you've never had any experience with MCUs, but a little exposure to programming.
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by adafruit on Wed Apr 18, 2007 6:10 pm

which digipots are you using?

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by mikewitt on Wed Apr 18, 2007 6:13 pm

ones I was able to get from microchip for free. I think they're MCP41010-I/P (or something similar) they're 10k pots, use SPI. I'm at the point where I know my subs are transmitting SPI-formatted communication, but I can't figure out why the pots aren't changing.

I can post code if someone wants it.
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by adafruit on Wed Apr 18, 2007 6:45 pm

i dont know that one but you can look thru the wavebubble code to see how i talked to the digipots used there. they're also spi.

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by mikewitt on Wed Apr 18, 2007 7:46 pm

(I think) my code does work, but I think that my instruction is malformed, and so the digipots don't understand the command.

I could be wrong though, and it is a fault in my code.

In any case, I'll get on it as soon as I have time.
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Re: Capacitance Measurement

by Olaf Marzocchi on Fri Oct 10, 2008 5:49 am

No news?
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Re: Capacitance Measurement

by mikewitt on Fri Oct 10, 2008 7:48 am

No, unfortunately I stopped working on it when another project came up. I never got the digipots to work, but I didn't try very hard. I'm sure that it was an error in my code, I just never got a chance to ever mess around with them for an extended period of time. I'm in college now, and I don't have the parts with me anymore as well, although I will still be working with microcontrollers.
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Re: Capacitance Measurement

by Olaf Marzocchi on Fri Oct 10, 2008 8:41 am

Thanks, I found the half finished board in a box so I am starting to write the firmware, but I'm a newbie.

My board is using 3+1 7 segments modules and two set of resistors, without digipot: with a switch I can shift the useful range of detection of (currently) 3 magnitudes:
R1+2xR2 1K makes readings in the 1.4mF..14nF
R1+2xR2 1M makes readings from 1.4uF to 14pF.

I supposed 1E0..1E5 Hz as useful frequency range of the 555.

I may choose to switch to 100 Ohm and 10M, in order to achieve 14mF .. 144nF and 144nF..1.4pF.

More than 100kHz should be possible with the 555, surely up to 300 kHz, so the minimum value could be reduced by a factor of 3 and I would have some overlapping of the ranges, while frequencies below 1 Hz should be possible but should be avoided: I read the 555 is stressed a lot and may fail.

Good luck with the college, anyway. I will post my results, someone may be still interested, since my project, without lcd, is about only 15 EUR.
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Re:

by Amberwolf on Fri Oct 10, 2008 5:36 pm

mikewitt wrote:Yeah, Q1 just turns off the 555 circuit. It helps eliminate noise when the device is being programmed.

In that case, you can eliminate the entire Q1 and associated traces, and simply run the /Reset pin to the AVR's output pin. You'll need to send the opposite level signal, but other than that, it does the same job. Holding the /Reset pin on a 555 low keeps it in a single state until you set the pin high and keep it there, so it'd be the most efficient way to keep it from running, though it doesn't cut off it's power completely. :)

There are also low power versions available, like (I think) the TLC555 by TI, which is what I ended up using in my ebike's wheel-speed transmitter to my PDA/speedometer running VeloAce.

The TLC555 is also capable of freq's up to probably 2Mhz, in case that matters. However, it's got a higher impedance, so it may change the values for the code you use to setup the timing resistors for measuring C1.
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Please be positive and constructive with your questions and comments.