For a project I'm working on I'd like to use reasonably accurate (say 1%) capacitors, which I hope to achieve by hand-picking (and if necessary combining) regular capacitors - I believe the film ones I've got are 10%. But I'm a little limited in the equipment for measuring them.
Ballpark range, say 100pF - 1uF (to be decided).
I do have a 'scope (a Bitscope - nice little bit of Aussie kit!) and a cheapo multimeter with a capacitance range, but I'm not sure how much I can rely on them for accuracy.
Looking around, most designs I see fall into one of two categories: a traditional bridge or an (often Arduino-based) timing-based setup.
But I have a problem with each. The bridges intended for capacitance measurement all seem to feature a capacitor in two arms, and I don't have an accurate one for reference. The timing-based setups all seem to assume the (say 5v) charging voltage is accurate - and I don't have an accurate voltage reference.
But it should be possible to get pretty accurate timing from something like an Arduino, and I have ordered some 0.1% 10k resistors, so I've at least got
something to work against.
I've only just started looking at this, and I could be way off the mark, but it feels like it should be possible to use a bridge with 3 arms resistance plus the cap under test (driven by AC). Alternately, going the timing approach, rather than assuming an accurate voltage and taking a single point in the charging curve, take 2 or more readings, work the sums from there. (Hmm, noticed a flaw there as I type - the voltage measurements would need to be accurate as well as the timing).
So I'm wondering how y'all might go about it.
This isn't at all a critical thing, but it does make a nice little exercise in figuring out how to bootstrap test gear.
The project is an analog computer (
https://github.com/danja/analog-computer), mostly a pile of op amps, the capacitors needed for the integrators. Even though I've been thinking about it for a long time, only recently gathered the components, got a load of breadboarding coming up next.
I'm thinking of using standard 1% resistors, maybe hand-pick, but gives me a baseline for accuracy.
So, suggestions?