#90: Measure Capacitors and Inductors with an Oscilloscope and some basic parts

This video shows how to measure the value of unknown capacitors and inductors using your oscilloscope and a simple pulse generator. There are many ways to do this, but this video focuses on just two basic techniques. The video was inspired by this blog post on scopejunction.com:
www.edn.com/electronics-blogs/...
The techniques are very simple, and are a good example of basic principles of RC and LC circuits. Another bonus is that it shows another use for the fast-edge pulse generator that was shown in a video I posted several days earlier on making your own basic TDR:
• #88: Cheap and simple ...
The capacitors are measured by simply measuring the RC time constant, and the inductors are measured by making a simple LC tank circuit and measuring the resonant frequency.
A copy of the video notes can be found here:
www.qsl.net/w/w2aew//youtube/M...

[@aqib2000]

The 8 divisions tip is epic

[@syedshigarfmashaam9974]

Even after 10 years, You're enlightening budding engineers like us. Kudos to you man!

[@petti78]

Some of the most clear, to the point and instructional videos I've seen! Wow, keep up the good work! A joy to watch and an effective way to learn some basics.

[@jeromekerngarcia]

Great bench technique to pass along to our younger players, & led me back to your "Fast Edge Pulser / TDR" one; which videos earned my subscription. Nostalgia for the many fast pulse edges & TDR work in my misspent youth!

[@mavamQ]

I'm enjoying your videos, thanks. Another easy measure on the scope is, 0.707 x 7 units = 5 units, useful for 3db points. Actual 4.949, closer than I can see! Edit: Reading my mail 2 years late, to describe how I do this a little better, I set the Volt/Div so the signal is more than 7 units and then adjust the variable knob for 7 units, then I make any external circuit adjustments until the signal drops to 5 units, this is the 3db point.

[@w2aew]

Oooh - that is very handy - thanks!

[@ZilogBob]

What a rarity! A KZbin video by someone who really knows his electronics theory, clearly explaining what he's showing, and with good audio at a reasonable level. Excellent! :)

[@Walter-Montalvo]

Zilog Z80?

[@ZilogBob]

@@Walter-Montalvo A little bit of Z80 a long time ago, and much more Z8. Now I've crossed over to the dark side with Microchip PICs. ;)

[@DucatiMTS1200]

One never gets around to doing back to basics but you have inspired me to do so. Your videos are so enthusing and fun. Keep up the good work. You are an excellent teacher.

[@JlerchTampa]

Reminds me of the electronics training I received in the US Army (circa 1991), straight and to the point highly effective knowledge transfer! Thank You!

[@DuanvantSlot]

Thank you. Got a new scope and your channel is just gold. :D

[@Dullthud007]

Thank you. There's loads of "what is an oscilloscope?" videos and loads of TY2603L-Mega reviews, but not so many "things to do with one" vids. Really liking your other vids too.

[@Greg-lo1tl]

I agree. Practical application scope videos are harder to come by.

[@nsknyc]

I have to say, I think I've seen most you videos maybe even twice. I really appreciate the effort you've placed with all this content. I accidentally found your channel looking for ESR measurements with oscilloscopes and saw that you have a plethora of info on radio stuff as well. Well I could go on and on... In short, I have to say thank you very much for giving us all these invaluable lessons!

[@daver1964]

Heh, me too! More than twice for a couple of them. This channel is a superb resource :)

[@wadehicks9270]

I've seen this explanation a few times so far yours was the simplest good work Sir.

[@mkschreder]

This is the best video on the subject so far. Well done!

[@Taran72]

Thank you for explaining this in so little time. It really takes a lot of skill!!! I'm watching your video for the first time, and I will definitely try to build the pulse generator. :)

[@x86cowboy]

Your videos are very educational & inspiring. Thank you so much for sharing. Please keep making more videos like this!

[@vanningale495]

Very nicely done. Thanks... I loved your signal source, and the parallel outputs to make the edge faster...

[@roundhouse283]

Great lab. What you just demo are is one of the first lab students perform in ac circuits courses. Brings back memories. You shot title your videos engineering lab ;)

[@VoidHalo]

I've had the money set aside to buy my first real scope and I've been researching and humming and hawing over this for some time. Watching this finally pushed me over the edge and I made my decision. Just bought a Hantek DSO5202P from Amazon. It has almost everything I wanted, except integration and differentiation. But as it is, this one as $470, which is about $150 more than I planned to spend. I decided it was worth the extra money for a 2 channel scope vs 1 channel. I get the feeling the extra channel will be worth it. My only regret is doing this at 5am when I haven't slept yet. I'm far too excited to sleep now. Listen to me gushing like a school girl with a crush. =D Now for my next dilema, buying a function generator.

[@w2aew]

Best of luck and learning with your new scope!

[@hoptoad]

Your videos are great, i'm learning so much. Thanks for the all the material and instruction.

[@alocin110]

Thank you for sharing this. Very thorough explanation with formulas. Great presentation. I liked your video.

[@marcusjenkins]

Using 74HC14 (as opposed to 74AC14), I'm getting 5ns rise time with 100nF + 3k3 RC. The squarewave runs at about 5kHz. The rise time seems to be pretty much independent of supply voltage between 2.5V through to 6V. I'm going to try packaging into an Altoids tin with 2xAA Alkaline => 3V supply. Mine's a Texas Instruments manufactured chip. I measured the rise time on my Owon DS7102V 100MHz Chinese scope. Compare this to the 350ns coming out of the scope's own 1kHz square wave probe calibration pins. 74HC14's are super-cheap and readily available in DIP on eBay. Thanks for a great circuit tip! EA5IGC

[@Pwaak]

Can't thank you enough for sharing your knowledge and these educational videos!

[@acmefixer1]

Great explanation. Uses a mathod I've never tried before. 👍 One thing that I've noticed is that just about everyone makes the assumption that their viewers already know what units of measurement the formulas will be using when they do the math. But that average neophyte electronics student doesn't know that all the calculations answers will be in units of farads and henrys, or even in ohms. They most likely assume that the units will be in microfarads microhenrys and kilohms. So these units really need to be explicitly stated. Thanks for this useful video.

[@syedhaider7121]

Thank you for a very informative video and presentation of techniques. I liked it and the best thing was the quality of video and crystal clear voice; rather commentary. You are a good teacher. Thank you.

[@ronjones4069]

You want to measure frequently at the zero crossings. It is hard to tell the peak, but the zero crossings are well defined. Also, it is more accurate to make the zero crossings as far apart on the CRT as possible either by adjusting the horizon sweep time or measure the time between a number of crossings and divide accordingly. It goes without saying that these zero crossings should all be the high to low or low too high crossings. Distortions in the wave can make your frequently measurement inaccurate if you measure half cycle times. Excellent video and I love your test fixtures.

[@dougkiss7630]

Excellent, extremely helpful, very well presented and spoken.

[@valiza123]

thank you for this guide, I used the 1khz test signal from the oscilloscope but worked perfectly.

[@tunicana]

watching your videos is a kind of great pleasure...thank you so much

[@friddevonfrankenstein]

Your videos are very informative. Just got me a free scope (70s Siemens Oscillar) and your videos are a great help getting started with it. subscribed ;)

[@CanadairCL44]

Now THIS is really interesting and well presented! You have a new subscriber! Thank you for uploading.

[@felixruiztorrez5192]

Such a beautiful oscillation. Thank you.

[@AxelWerner]

MORE! MORE!! MORE SIMPLE TESTING AND MEASUREMENT TOOLS FOR DIY: great timeless content like that is worth like GOLD! THANKS A LOT, OM! 73!

[@jspencerg]

Thanks for clear instruction and demonstration of this measurement. I was lucky to find a 2467 in January. I need to study the manual better. Very nice functionality.

[@CharlieTechie]

Good, simple video. Thanks for sharing with us.

[@jasoneyes01]

Figuring out unknown variables is alot of fun this way. Thanks!

[@w2aew]

Yea - it's kind of like firing up the lawn tractor to mow a tiny patch of grass - a bit overkill on the equipment side, but a lot more fun!!

[@henrihoopkins2822]

Great video. One of the best that I have seen. Now I can measure the C 's that I have to see if the value is as marked, the same for the L's I have. Since I am a retired EE I like to know the value as to how close the value as marked. I suggest that the value for measuring C's I would make the resistor 1% or better. The same applies for the C's to measuring the value L.

[@larrybud]

You could always measure the resistor so you know the actual value

[@Darkblue332]

Simple and effective method . Thank you for sharing .

[@JohnSmith-gp1kr]

Great video!!! Do you know how to measure the inductance "online"? This is when it is loaded, i.e. current flows through it and in the same time the inductance changes (ex. the core varies)? It's difficult but can be extremely useful.

[@psycox8758]

Just what I was looking for ! Love your vids. Many thanks :)

[@silasfatchett5693]

Very interesting video, lots of useful information. Thanks.

[@jimifarrell3667]

well i found out my function generator uses the max038 chip witch the data sheets said square wave rise and fall for both are 12ns so i guess your circuit would work so i will build it thank you for your help in answering my questions even i majored in electronics in high school i forgot some and guess some things didnt stick because i must not of fully understood either but with your teaching i see it in a whole different light thank you again

[@ronaldlijs]

Nice one Alan, thanks for this educational video excellently explained again!

[@wernerlopez5433]

Alan, Thank you very much for the quick answer. I will really appreciate if you can share some quick tips meanwhile video is on the way. Congratulations for your Amazing job and to share all this tips.

[@yoramstein]

Nice video, nice clear English with easy talking.

[@sstrama]

Pretty good presentation. In text below here, links to general information can be provided such that others can refer to details too.

[@AltayBrusan]

Thanks for great contributions. How does the probe capacitor effect or side effect the results? On so datasheets (e.g. sensor ICs) in the test setup section, I saw they mentioned that the probe impedance too.

[@46bovine]

Great vid, I just found your channel. Will keep viewing.

[@rolfw2336]

I really appreciate your very hands-on review of basics! Quite useful. But, I imagine there is some limit to the range of capacitance if your input waveform is set at 5-6KHz.

[@w2aew]

The capacitance measurement is made by looking at the risetime of the signal (the RC time constant), so the frequency of the signal really doesn't enter into it, as long as it is low enough to permit the RC circuit to fully settle before the next half cycle.

[@Soupie62]

When a work bench starts to get crowded, a decent calculator [or phone app] makes more sense than a laptop or PC.The 15C is a good model, too

[@bm830810]

love your presentations, thanks a lot

[@keithcoltron3171]

Excellent contents/presentation, many thanks

[@SimpleEnough2k9]

At first glance, it seems to work with calibration output of the scope, although there might be some limitations. For example, on my scope, the rising edge of that signal is about 3.5us, therefore if we estimate that the rising time is the required time to go from the 10% up to the 90% of the signal amplitude, that would be about 2.197 times tau. Under those circumstances, if we want to see the complete signal, from 0 to 5 tau, with a 1k resistor, I would be able to estimate the capacitors values from about 1.33nF and up. Overall, there is always a way, but we need to experiment and do some homework to understand what is happening.

[@jvcrules]

Thank you for showing this. I've been trying to measure inductance with my scope for some time now, but I could never figure out how to do it correctly.

[@carriersignal]

Great video as always. Thank you!!

[@darqen271]

Great videos, Self teaching EE here.Thanks!

[@markussteinbacher8807]

great video. thanks. Could you tell us how to measure the Q factor, R(ohms),dissipationfactor of a coil on scope please ?

[@Debraj1978]

You used the rise time measurement for "C", and used the frequency measurement for knowing "L". We can as well use the frequency measurement for determining the "C" as well, when we have a known value of "L". Very resourceful video indeed.

[@mikesamra9126]

Always great videos.

[@corporallee44]

Excellent presentation

[@hackercop]

Really informative video thanks. I need to measure some inductors for a induction heater

[@SuperJetjockey]

My function generator is on its way, so I had to use the square wave generator on my 475 scope. It worked!

[@Loscha]

Always great stuff!

[@Linksimpson]

Really impressed with your videos. Thanks somm

[@ElPasoTubeAmps]

Very nice presentation - thank you

[@jix177]

Another interesting video. Thanks for sharing.

[@belltolltothee261]

Very good explanation.

[@dinnade9338]

Best as as always ... thanks for sharing your knowledge to the workd

[@user-su5sq5ib3i]

Thankkk youuu alllann!!!! I needed this right now

[@radioboyable]

Great little video.

[@jimarcin]

I totally agree : ) Great videos man, keep it up!

[@nnamrehck]

You make this stuff look easy!

[@bullshyte8585]

Thanks for a great treatment of my scope junction blog! Nice setup; when I do this I just slap-solder the parts together in the air. One point needs comment - for very small capacitors one needs to measure the capacitance of the fixture and the 10:1 scope probe first with the same technique so the probe and fixture capacitance can then be subtracted from the final measured value when the cap under test is added to the RC circuit. The LC circuit is also known as a "tanktwanger" since the effect is so similar to twanging a guitar string.

[@w2aew]

Glad you liked it, and good common sense advice of course.

[@mikefinn2101]

So glad you have taken the time to make these very helpful videos for free. It was very well done PH D style great job many thanks 73's wb7qxu

[@skycarl]

Always good stuff. Thanks.

[@Starbuckin]

Excellent video!

[@TheCrazyStudent]

Great presentation as always! I've always been wondering, in an LC tank circuit, if the L and C were not physical components but parasitic L and C which is causing unwanted ringing on the output, what can be done to eliminate the ringing in order to get our clean square wave back?

[@thomasmaughan4798]

You cannot entirely get rid of it but if you can get some resistance in there it will reduce the "Q" and quickly damp the ringing. You can sometimes also use clamping diodes.

[@barn5923]

THANKS VERY MUCH I ENJOYED ALL YOUR VIDEO.

[@Lyrics9801]

the best results that i've ever had was with the Gregs Electro Blog (i found it on google) without a doubt the most useful info that I've tried.

[@bekiryufka]

Bro that worked pretty good. Thanks for advice you just saved my hours. 😘

[@windytan]

Thank you, very illuminating.

[@manojgceb]

This is awesome... Is it ok to use calibration output points on the scope ( most scope have 5V p-p and 1KHZ waveform) for as a fast edge source?

[@wernerlopez5433]

Hi Alan. I am impressed with your work and the quality of your videos. I am looking for a way to measure complex impedance of a circuit at resonance or in any other frequency using the oscilloscope, is this doable? Thanks , Werner.

[@oswaldocunha9455]

Very neat and clever .Thanks a lot !

[@hans-jrgenbernhardtsen8506]

Instead of the fast pulse generator, can I use a piezo ignitor? Thanks for the very informative videos 👍

[@acestudioscouk-Ace-G0ACE]

Clever and useful, thank-you.

[@sheaton319]

What are those terminal strips that you have soldered to plug in components called? I'm trying to find some online but don't know what to search for. Thanks Edit: Never mind, found out they are called machine pin sockets.

[@t1d100]

Hi, Alan. Another great video! Thanks for your efforts! Is there any way to add a DC offset to this circuit, to test caps at their working voltage?

[@thomasmaughan4798]

Conceptually it is trivial; just put a blocking capacitor from the square wave signal source to the device under test. Then, have a mechanism to not instantly apply the DC (rc time constant; a resistor and filter capacitor feeding the device under test). If you simply switch high voltage on the device under test some of that is going to go through the blocking capacitor into your pulse generator.

[@gkdresden]

With your ground free battery operated steep egde pulse generator you can use also the same circuit for the inductor as for the capacitor. It is not necessary to build up a resonator. Also the error is increasing because its much easier to get a tightly tolerated resistor than such capacitor. In the inductor case you just need to clamp your oscilloscope aross the terminals of the resistor to observe the voltage rising, which represents the current rising across the inductor. The math behind is the same.

[@dmottern1952]

Very good video!

[@XPFTP]

i dont see a math video for the caps.. iam testing a 473 cap. and i can not get it to add up..the old scope i use. i set the T/D on main dial.. the screen doesnt give any info. i count left to rite 4 of the 5 subgraticules. t/d set to 50u. 50/5=10 10/1000= 0.01.. thats with the 473 in place.. so iam lost.. lol if theres a video or something i can see.. would be cool.. the trace is at 8D. if i go more it slopes over more. or is that what we want. as much slope to the flat. thank you kb2wvo

[@tonythediyer8537]

Nice video! Thanks for the tutorial. I guess you could use a function generator to accomplish this? I don't recall seeing what frequency that you used for the square wave pulses. Are the input pulses at 5 volts?

[@w2aew]

1-10kHz works fine. Yes, a function generator can be used. It was 5Vpp in this case.

[@jamesoram7098]

Great video. Thanks!

[@Vahidutube]

Great, great job Sir...

[@marcusjenkins]

I just checked my Owon DS7102V. 350ns rise time on the 1kHz calibration square wave with probe on x10. :-o. I ordered some HC parts (the AC ones are hard to get on eBay in DIP) and I'll be making one of the oscillators. I'm hoping to get something like a 15ns edge transition from HC. The first use will be to tweak some air core 700nH coils for a 20m low pass filter. Thanks! EA5IGC

[@maziarghorbani]

Great video.

[@Mydrac]

Thank you, very nice video. When I grow up I wanna be like you.

[@ronaldschild157]

I love that vintage Hewlett Packard calculator 😃. Take care of those and they will last a lifetime, as you are obviously doing.

[@martinsleguizamon]

Is there a way to measure the selectivity (Q) of that LC tank circuit with the oscilloscope ? Thank you.

[@w2aew]

One thing to remember that the Q will depend on the circuitry around it (loaded Q). So, you'd have to measure it "in-circuit" - usually by sweeping a signal through it.

[@andrewferg8737]

Great video. Do you think this set up will work in the micro or nano Henry range? It seems I'm always guessing with small value coils...

[@w2aew]

It might work for higher uH values, but don't think it would work well for nH level measurements. The parasitic inductance and capacitance of the fixture will be the limiting factor.

[@virgogreg]

all info no fluff thanks!