Thanks, that's my design. I've built a few of them and sold them, first one around 1980 but those with 50uA meter movements. That one I built in 1985 with some parts I had on hand, so it is built with a surplus control that has a volume control (used for zero set to cancel wire capacitance) on a 1/8 inch shaft in the center of a SP5T rotary switch. The case is a clear orange plastic box, I think it had a bottle of perfume in it at some time.
Yes, it is very stable. Use a 5V regulator. I put a momentary pushbutton on mine for power, it draws very little power so a 9V alkaline battery has lasted years.
I started building a mini version to fit in the pocket of one of those Radio Shack pocket DMMs, using supermagnets and some tiny reed switches for the range selector. Never quite completed it, now I'd use a PIC with capacitance switches and its own LCD display. Actually I'm working on a design for a combo capacitance meter and ESR to fit into a compact case. Yes, I know I can buy one, but the point is for -me- to build it.
If we're going to talk more about the design, we should move over to the Electronics_101 list.
Steve Greenfield
--- In Homebrew_PCBs@yahoogroups.com, "sailingto" <sailingtoo@...> wrote:
>
> Steve, that is a very good idea - I'm not all that concerned about true accuracy, just so I can tell a .1 from a .01 cap. You mention seeing change as you wave your hands about - is it stable enough?
>
> I would be interested in building one of those - I do fool around with uC some - that would make a neat project to display on a LCD.
>
> Thanks for posting.
>
> Ken H>
>
> --- In Homebrew_PCBs@yahoogroups.com, "alienrelics" <alienrelics@> wrote:
> >
> > A couple of 555 timers makes a surprisingly accurate and sensitive capacitance meter. Uses your DMM in 200mV mode. In the lowest setting, 1mV = 1pF. Measures down to 0.1pF resolution, keeping in mind it isn't that accurate, but you can see the capacitance change as you wave your hands around.
> >
> > http://www.polyphoto.com/tutorials/ElectronicCircuits/
> >
> > Build it with parts from your junkbox for next to nothing.
> >
> > Or if you can program microcontrollers, do the same thing in software. Regular clock followed by a monostable, the cap under test is in the monostable. Measure the time it takes to charge the capacitor.
> >
> > Steve Greenfield
>