Suggestions for demo circuits for an Oscilloscope 101 workshop - Page 1
Forum section: electronics / general

author: techy101
author_rank: Unknown
timestamp: March 20, 2018, 05:53:46 pm
content: I'm going to be teaching an Oscilloscope 101 workshop at my local makerspace and am trying to figure out a collection of basic signals and circuits to demo and let them probe. Basic square and sine waves are of course on the list, but I'm also trying to come up with some demos that can't be solved with the auto-set button. The target audience are people who have probably used a DMM and an Arduino, but have not used an oscilloscope before. My plan is to keep it to the very basics of what it is, why it's used, basic operation, and some hands-on time.It's my first time doing something like this so I'm somewhat intimidated by the prospect and I'm not quite sure where to look for ideas, so I'm here. I've got just barely enough time to spin some small boards for ease of demo circuits if that's a route I decide to head down.If you were just learning what an oscilloscope was, what kinds of circuits would be most helpful to see?

author: mdijkens
author_rank: Regular Contributor
timestamp: March 20, 2018, 06:37:37 pm
content: As a real beginner and limited scope experience I would think of:- measuring and calculating capacitors- measuring power with CH1 x CH2 of Arduino/ESP8266 boot/sleep- noise measurement on SMPS and effect of different caps- investigate Arduino and/or 555 PWM and cleanness of signal with higher frequencies- Investigate arduino+servo pulse-lengths- Determine blowup time of LED on 5V- ...As I said... I'm still a noob

author: tggzzz
author_rank: Super Contributor
timestamp: March 20, 2018, 07:07:28 pm
content: Show what poor construction can do to a digital signal.Make a counter on a solderless breadboard. Make sure they have long long wires with insufficient decoupling.Use a 10cm scope probe ground lead, and then a 1cm coiled wire ground lead, and see the difference.And, of course, try your demos beforehand to see the circuit fails and works as you wantLastly, don't be worried - they regard you as an expert, and you probablyarethe local expert!

author: rstofer
author_rank: Super Contributor
timestamp: March 20, 2018, 07:32:46 pm
content: Toss in the Arduino and show UART, SPI and I2C decoding if the scope is capable. Even if decoding isn't available, arrange to trigger and show the data transfer.Definitely show the charging voltage on a capacitor. Maybe a 1k resistor feeding a 0.1 ufd capacitor to ground. Feed it with a signal generator or even a 555 timer set at an appropriate frequency. Turn the probe around and watch the current waveform by probing across the resistor (as long as everything is floating). Or change the circuit such that the input goes to the capacitor and the series resistor goes to ground (differentiator circuit).You could show the attenuation versus frequency for the same circuit. Find the 3 dB point.

author: mdijkens
author_rank: Regular Contributor
timestamp: March 20, 2018, 08:14:54 pm
content: Quote from: rstofer on March 20, 2018, 07:32:46 pmI'd love to find out what this is

author: bitseeker
author_rank: Super Contributor
timestamp: March 20, 2018, 08:27:49 pm
content: For makers with Arduino, some good stuff to start with include things that otherwise aren't easy to see.- PWM output from the Arduino- Convert PWM to analog and see how it changes with different component values- Why you need decoupling capacitors (i.e., how they clean up noise)- Protocol decoding, as rstofer pointed out- How to use single-shot capture (view switch/contact bounce, voltage transients, turn-on overshoot, etc.)

author: lordvader88
author_rank: Frequent Contributor
timestamp: March 20, 2018, 08:50:02 pm
content: LC oscilator's, like Hartley or Colpit's type, with a BJT or JFETOnly a handful of components and should seem a lot more real than some Arduino signal imo.

author: abraxa
author_rank: Frequent Contributor
timestamp: March 20, 2018, 11:02:41 pm
content: Quote from: rstofer on March 20, 2018, 07:32:46 pmAs much as I like your idea, I would advise against any measurement where the ground lead is not connected to ground. Sure, it works when the circuit is floating but doing this will encourage the audience to do the same on other circuits: "it worked there, so it should work here, too". If they do it on a non-isolated circuit... yeah, I'd rather not. Best to avoid showing them cool tricks that could get them into trouble because they don't understand when it works and when it doesn't.While it may be simplifying the facts, it may make sense for techy101 to tell the audience that the ground lead must always be connected to ground, meaning that each probe can only measure a voltage relative to ground. Sure, it's not the whole truth, but it's not wrong either and prevents them from blowing up stuff.I really, really like the idea to show contact bounce (any simple switch or button will do, ideally with a connected logic gate on a different channel to correlate), to show voltage across an RC filter (as above), overshoot/undershoot/ringing on wrongly terminated logic lines (nice way to introduce transmission line theory, which would allow you to seamlessly explain why a short ground spring is preferable to the ground lead), examining an Arduino's power supply noise when a DC motor runs from the same (allowing you to make mention that this is why those supplies are usually separate), etc.Essentially, I suggest you choose subjects that aren't too difficult to understand while still applicable to electronics and the Arduino world in particular.Also, I'd like to note that it's not always about the circuit - it's also learning how to operate the scope to make measurements (by eye or by cursor). Even a task as simple as determining a signal's frequency by eye may prove to be a challenge for some. I'd say that that's a basic skill, though, so it should be part of the training. It also makes the audience more familiar with the controls of the scope (V/div settings, horizontal offset, vertical offset, etc.).

author: techy101
author_rank: Unknown
timestamp: March 25, 2018, 05:22:23 pm
content: Thank you all for the suggestions and sorry for the slow reply, I've been laid up sick for the last week.I'm trying to be careful to keep the scope (sorry...) of the workshop limited to operation of the oscilloscope and not delve into teaching basic electronics. However it seems like that could be a difficult fine line to walk. I also don't want to totally overwhelm people. If this goes well I'll probably set up an intermediate topics class.The class is set up for three hours. I'm figuring the first 1.5-2 hours will be spend covering the basics of what an oscilloscope is, a tour of the interface, what the terms mean, manual setup, automated setup and it's limitations (I'm torn on this, but experience has shown that people will use it and I'd like to make sure they understand what it can and can't do), single-shot capture, and taking measurements. The last 1-1.5 hours will be hands-on time looking at circuits.Based on the feedback here I'm thinking that I'll have the following available to look at:* Sine wave from a function generator* PWM* Contact bounce* Capacitor charge/discharge* Over/Undershoot on digital signals* SMPS noise* Good vs poor measurement techniqueQuote from: rstofer on March 20, 2018, 07:32:46 pmI'm inclined to agree with this. I volunteer with a FIRST robotics team and run into this regularly. The approach I've become a fan of is to tell them (either before or after the explanation, depending on the topic) that I am simplifying some things and that it's not the whole truth. The kids respond well to the honesty and don't seem to mind that they're not getting the whole story, as long as they don't think they are.The class is in two weeks, so I've got a lot of prep work to put things together. I'll update on how it goes when it's done!

author: tggzzz
author_rank: Super Contributor
timestamp: March 25, 2018, 05:34:52 pm
content: Consider giving them some short pre-workshop reading about what's in a scope and what the controls affect. Optionally add points about basic concepts such as how to calculate the frequency given the interval.I wouldn't bother with a video, sinceyouwill be the video during the workshop - and you want something that complements your performance.

author: David Hess
author_rank: Super Contributor
timestamp: March 26, 2018, 12:56:16 am
content: Have them examine the reverse recovery time of a diode in a switching power supply circuit. Autoset will lock onto the switching waveform but altering the position and magnification will be necessary to isolate the reverse recovery. This might be easier and more informative with a reverse recovery test circuit driven by your square wave source.

author: ez24
author_rank: Super Contributor
timestamp: March 26, 2018, 01:39:46 am
content: Quote from: techy101 on March 20, 2018, 05:53:46 pmSounds like a good idea for a YT video like w2aew:Might get some idea from these YTers:https://www.eevblog.com/forum/other-blog-specific/oscilloscope-youtube-video-channels-my-pick-of-the-best-do-you-know-any/msg1295416/#msg1295416But it probably would take you too long to go through them.I like the switching noise and switch bounce ideas.

author: amyk
author_rank: Super Contributor
timestamp: March 26, 2018, 02:23:57 am
content: Just for fun...https://www.eevblog.com/forum/chat/surely-i'm-not-the-only-one-who's-seen-oscillofun/https://www.eevblog.com/forum/chat/beams-of-light-new-scope-demo-like-youscope/https://www.eevblog.com/2011/03/08/eevblog-153-youscope-demo-on-a-digital-scope/

author: bitseeker
author_rank: Super Contributor
timestamp: March 26, 2018, 02:25:48 am
content: Quote from: techy101 on March 25, 2018, 05:22:23 pmLooking forward to hearing how it went, what worked, what didn't, etc.

author: nctnico
author_rank: Super Contributor
timestamp: March 26, 2018, 05:05:40 pm
content: IMHO:- basic signals like sine wave and doing measurements- XY-mode- contact bounce- limited swing and slew rate of opamps (distortion/clipping)- protocol decoding

author: ogden
author_rank: Super Contributor
timestamp: March 26, 2018, 05:18:49 pm
content: Quote from: nctnico on March 26, 2018, 05:05:40 pmI would check existing scope demo board specs first, only then think what to do next:https://www.tek.com/lab-course/learn-digital-oscilloscope-operations-using-arduino-board-dut-signal-generatorhttps://www.keysight.com/en/pd-1952427/educators-training-kit-for-infiniivision-2000-and-3000-x-series-oscilloscopeshttps://www.siglentamerica.com/accessory/stb-3/