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Old 22nd March 2009, 10:12 PM   #1
radtech is offline radtech  United States
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Join Date: Dec 2006
Default non PIC capmeter

I was just looking at the PIC capmeter thread and thought I'd dig this little baby out... thought some of you might find it interesting.

Click the image to open in full size. Click the image to open in full size.

It's a capacitance meter I designed when I was a teenager close to 30 years ago, when there weren't many available and they were way out of my price range.
This particular one was built around '85.

It's based on a 555 timer. The timer outputs pulses whose width varies with the capacitance connected, the pulses then gate a clock which is counted by a 3 digit BCD counter IC and displayed on an LED through a BCD to 7 seg decoder. A quad nand gate is used to develop reset and latch pulses, and a second 555 stretches the reset pulse to zero the meter.

I saved money by using the counter chip's built in multiplexer as the clock signal, and the small LED was driven directly by the chips, no buffers or current limiting resistors.

It has 2 ranges, .001uF to .999uF and 1uF to 999uF. I did have another version that would display picoFarads by dividing down the 555 pulses.

Altogether it probably cost me $15 to $20 in parts availabe at Radio Shack at the time.
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Old 22nd March 2009, 10:26 PM   #2
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Join Date: Jan 2006
Location: Johannesburg, South Africa
That bubble lens 7 segment display brings a pang of nostalgia!
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Old 22nd March 2009, 10:54 PM   #3
Dr_EM is offline Dr_EM  United Kingdom
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Join Date: Oct 2006
Location: Swindon
That's cool! Not knowing any programming this is the sort of thing I would build if I needed a capmeter! Much more fun to develop anyhow imo
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Old 23rd March 2009, 05:37 AM   #4
dangus is offline dangus  Canada
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Join Date: May 2004
Location: Vancouver Island
One of my non PIC capacitance meters looks like this:
Click the image to open in full size.
I feel like Dr Frankenstein when I use it.
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