Comments on: Simple capacitance meter

By: Noah

Noah — Thu, 15 Mar 2007 06:53:59 +0000

Hey, that’s the radioshack 300-in-1 kit! I have one of those…

By: Mike

Mike — Thu, 15 Mar 2007 00:39:49 +0000

@ledtester
I saw the first one when I was designing my circuit, but neither the design nor the math behind it is easy. With the second one, the design is simple, but has a higher parts count, even though the math is easier. With mine, all the equations I use can be found from the basic formula t=R*C. Just solve for a different variable, and you have a relatively simple equation.

@person
If your multimeter has frequency counting, use that, and solve the equation 1/(freq*R)=C, where R is the sum of the values of r1 and r2. This is how I did it when I was using my scope (using just the frequency function), and it works very well. If you want voltage, look at this: MRF24J40-I/ML, it’s a Frequency to Voltage converter in a DIP package, I don’t know if that’ll work entirely, but my samples should arrive next Monday, so I’ll know then.

By: ledtester

ledtester — Wed, 14 Mar 2007 21:46:14 +0000

Another good design for an LC meter is this one:

http://www.cappels.org/dproj/nlglcm/Pretty%20Good%20LC%20Meter%20Project.html

or this:

http://www.antennex.com/Sshack/aade/specs.htm
(schematic at end - also includes theory of operation)

By: kyle

kyle — Wed, 14 Mar 2007 17:01:23 +0000

very handy!

By: person

person — Wed, 14 Mar 2007 16:20:48 +0000

I would like one too.I had the idea a few days ago so I have thought about it a little.Here's what I want.
http://cgi.ebay.com/Smart-Tweezers-Capacitance-Inductance-Meter-DMM-agilent_W0QQitemZ250091364185QQcategoryZ25412QQrdZ1QQcmdZViewItem
It would be perfect for salvaging the unmarked surface mount capacitors on junk boards.
But if I built my own I want one to attach to my multimeter that converts to resistance or voltage.The circuit they show the 555 timer is doing most of the work .It could probably be adapted to anything that could do the time to capacitance conversion and display.Nice work to the designer though for keeping at it till it was done.

By: twistedsymphony

twistedsymphony — Wed, 14 Mar 2007 14:20:08 +0000

awesome… I’m building one :)

By: HaX80r

HaX80r — Wed, 14 Mar 2007 13:57:43 +0000

Wow! This will help with my science project for school. This is exactly what I need, and it’s better than discharging a cap through a volt meter and timing the drop to 1v. Thanks!

By: japroach

japroach — Wed, 14 Mar 2007 11:50:06 +0000

If the cap has an internal short, etc. then yeah it should tell you that the cap is bad. If its been in storage for a while, it may read a bit low but still be ok after reforming.

However, the main failure of electrolytics afaik is increase in ESR. This may affect the C reading of his circuit, but it doesnt look like it would be noticable.

But google ESR meter schematics if you require this, they are not too complicated to build.

By: Dave

Dave — Wed, 14 Mar 2007 10:22:33 +0000

so this could be used to find out if a capacitor has gone bad?

By: Crash

Crash — Wed, 14 Mar 2007 09:02:40 +0000

Cool…