Finding Capacitance with an Oscilloscope

Overview of finding the value of an unknown capacitor using and oscilloscope. It's important to note that different value capacitors and resistors as well as voltages will influence the way your graph looks. I hope this helps!

[udohchiemezie]

its strange to see that there are no comments yet... Trust me, you have helped me to solve a problem with your clear explanation. Nice one!

[adamnoble]

I like the way you organize and break it down

[HitAndMissLab]

great video. just what I needed and clearly explained.

[bobisyouruncle]

Just want to mention that 'e' is 2.718

[jacktuber]

I just got a single channel analog oscilloscope, I'm learning to use it. This is helpful. I want to try this

[rajaqamar]

Question: Patch a RC circuit and connect it to AC input voltage source. DIsplay the voltage waveform of capacitor voltage and waveform of capacitor current simultaneously without using MATH mode of the oscilloscope. Use oscilloscope only to get the desired result.

[EngineeringVignettes]

Well presented. I know it can be challenging to get ones thoughts out while taping and drawing, and sometimes when I forget what to say next :)
Just a few thoughts from me on your demo, pls feel free to consider or ignore.
- signal generators usually have a built in 50 ohm resistor, this may throw off calculations if not actually measuring the output of the generator. I think your were doing that though, but viewers may not have known about the internal impedance.
- t = RC --> C = t/R : just divide both sides by R ? :)
- more for ppl with analog scopes but the way to minimize errors when reading datum points off of a waveform is to try and use as much of the screen as possible, eg. have only one cycle on screen and at max possible amplitude. The effective resolution between divisions is really only a tenth or fifth, hard to get any more accurate.
- getting into electronics, its handy to be able to seamlessly move between the capacitance scales (uF, nF, pF) = (10^-6, 10^-9, 10^-12) in one's calculations. This takes practice though. Same really for reading resistors by colour (though rarely seen now due to wide use of SMDs)

It nice to see you working it out on paper, I tend to do that too but I'm more from the old school.

Cheers,

[bestechdeals]

I just wish I had seen this earlier; we are asked the same exact problem ad I messed up

[sanjursan]

Wow, I just noticed that you have videos of a digital clock and circuit. It would be really neat if you could mod it a bit to become a stopwatch that could be started and stopped by some external switch, such as the switch of a power supply, better, by voltage values. Then you could measure caps with accuracy! Oh wait, what about reactance vs impedance? Hm, interesting since there is no frequency in the circuit. Hmm.

[sanjursan]

Well you are only off by 40%! Try this: pick a resistor such that RC > 5 sec. RC > 10 sec is even better. If the Cap is really unknown you must experiment a bit to make it work. Then use a DC signal of 10 volts and use your cell phone stop watch app to time the step in volts from zero when you switch the PS on to when it reaches 6.32 Volts. Then divide by the resistance to get the capacitance. Be sure the cap is completely discharged before you start and you should get a value accurate within a few percent. I usually run it three times and take the mean, but if I am careful the time repeats within a few tenths of a second. The longer you can make the time measurement, the better the accuracy because (delta t)/t gets smaller, where (delta t) is the variance in your time measurement. Try it! Also, you will find that, unless you have a top digital scope, the scope method is quite sensitive to frequency. You may need to go down to below 1 Hz for caps, and your analog scope will not like it! Plus eyeballing points on the trace simply cannot get the accuracy of using a stopwatch, by about two or three orders of mag. I have used RC pairs such that Tau was several minutes. And I use a big faced analog volt meter, a Simpson 314 for timing. With long times, the needle is moving so slowly that accurate timing is quite easy. Plus, with the analog meter with full scale numbers of 10 and 30, with the range set on 10 volts, the 6.32 volts hits right on the "20" of the 30 volts scale right below it! While there plenty of videos on the scope method, I am yet to see anyone post a video of the stopwatch method. How about you go through the details and make the post of the (way better!!) stopwatch method. Anyway, good luck with your studies.

[faroutaamri]

5:30 that's one beautiful curved bracket