USB Oscilloscope for undergrad student  - Page 1
Forum section: electronics / testgear

author: Ronny
author_rank: Contributor
timestamp: April 05, 2017, 04:52:44 am
content: Good night everyone,I am in an exchange program in the US and I want to bring an USB oscilloscope back to my country (Brazil), one of the big boys is out of question for me, it has to fit in my bag.It will be used for basic stuff, reading serial that is going to a PC, checking basic circuitry for undergrad level classes, etc.To be honest I don't have a specific budged, I would like it to be around $80, but if there is something good for a little bit more I will get it. For instance, I was going to buy an Owon just short of $ 100, but I thought it is a good idea to ask the pro guys first.I just want something that is safe enough so it does not fry my laptop, and that is precise enough for the basic undergrad stuff (I see no problem if it is a big tougher)Thank you very much guys.

author: Gyro
author_rank: Super Contributor
timestamp: April 05, 2017, 09:56:42 am
content: This is the VDS1022(i) teardown thread. I assume that's the one you're looking at from the price indication. The other decent option would be the Digilent Analog Discovery.https://www.eevblog.com/forum/testgear/owon-vds1022i-quick-teardown-(versus-the-hantek-6022be)/

author: Ronny
author_rank: Contributor
timestamp: April 08, 2017, 01:58:37 am
content: Quote from: Gyro on April 05, 2017, 09:56:42 amYeah, that is the one.In you tear down you seemed quite positive in relation to it. I quite like this one and you just backed it, unless there is someone else to recommend another one I think this will be the one.Thanks!

author: TK
author_rank: Super Contributor
timestamp: April 08, 2017, 02:59:00 am
content: If you still have student status, you should try the Analog Discovery 2 by Digilent. 2 channels scope, waveform generator, logic analyzer, bode plot. List price is $279 but academic price I think it is less than half.

author: Ronny
author_rank: Contributor
timestamp: April 08, 2017, 03:32:04 am
content: You guys mean this one?http://store.digilentinc.com/analog-discovery-2-pro-bundle/Well, if I get 50 % discount, I am fine with the price, especially with this neat bundle.I have never seen this one before, looks neat. Is it that much better?Edit: Is it isolated ?

author: ebastler
author_rank: Super Contributor
timestamp: April 08, 2017, 09:11:41 am
content: Quote from: Ronny on April 08, 2017, 03:32:04 amThey don't seem to offer academic pricing on that bundle. But they do on the basic device:http://store.digilentinc.com/analog-discovery-2-100msps-usb-oscilloscope-logic-analyzer-and-variable-power-supply/.Look for the green "get academic pricing" button.

author: Fungus
author_rank: Super Contributor
timestamp: April 08, 2017, 12:43:02 pm
content: Quote from: blueskull on April 08, 2017, 09:15:34 amItcanbe.It connects to the USB port of your PC so it all comes down to if your PC is isolated or not. Many laptops are.(especially if running on batteries)

author: Fungus
author_rank: Super Contributor
timestamp: April 08, 2017, 12:44:16 pm
content: Quote from: Ronny on April 08, 2017, 03:32:04 amQuite old, but:

author: Ronny
author_rank: Contributor
timestamp: April 08, 2017, 05:43:12 pm
content: Well, I was seeing some stuff about this thing, it is freaking cool, it is not just an oscilloscope, it has the full package.I applied for student discount, lets see if they give it to me. Sounds really good, if someone has a better option, you have until they approve my student discount to convince me, because I am totally buying this oneBy the way, if I use this with a laptop running on batteries I don't think not being isolated will be a problem, I can live with that. It is a shame that they did not do it tough, such a cool little product.

author: rstofer
author_rank: Super Contributor
timestamp: April 08, 2017, 06:54:43 pm
content: Quote from: Ronny on April 08, 2017, 05:43:12 pmI would recommend the AD even at full price. You simply can't get the assortment of gadgets at anywhere near the price and being able to dump it in a backpack is a definite plus. I have the original version. I also have the new Digital Discovery. Both bought at full price... They don't have an 'old geezer' discount.Isolation is an interesting problem and it's the USB system that needs isolating. There are commercial isolators around but the cheaper ones are quite slow. I plug my AD into a powered USB hub and hope for the best. Actually, I don't hope, I think first.The AD is not the device to use on high voltage switching mode power supplies. It works perfectly well on low voltages. If you are uncertain, measure the voltage with a meter.The vast majority of my projects operate at 15V or less - usually much less. The AD is perfect for uC projects, tuned circuits, amplifiers, digital logic and so forth. Measuring mains is out of the question. But wait to you see your first Bode' plot! Magnificent!You want the Pro Bundle because you get the scope probe adapter. You will want to buy a couple of x10 probes (Digilent has them) and this extends the voltage range quite a bit. Be aware that if you use the adapter (and you should), the signal generator outputs are ONLY on the BNCs. You will want to get a couple of BNC->grabber test cableshttps://www.amazon.com/Oscilloscope-Probe-Test-Cable-Mini/dp/B00WZVY5JE/ref=sr_1_13You can use the grabber cables for the scope input but it's nice to have the x10 capability of a real scope probe. Plus, you can adjust the probe compensation on a real probe.

author: Ronny
author_rank: Contributor
timestamp: April 10, 2017, 06:35:24 pm
content: Quote from: rstofer on April 08, 2017, 06:54:43 pmThanks for the tip. Just ordered the BNC grabbers. Digilent has not given me student status yet, still waiting for it.I will definitely order the BNC adapter board and some probes with it!I am ok with it not being isolated, I will have a rule "Always use it with my laptop running o batteries". I think that is enough to avoid trouble.

author: Ronny
author_rank: Contributor
timestamp: April 12, 2017, 12:25:01 am
content: Turns out the discount is not as great as I thought it would be.410- 321 Analog Discovery 2 Scope & Logic Analyzer $279.00 36% $179.00If I add the BNC board (20) and the probes (20) it jumps to 240.I can afford that (in tears), you guys think it is worth it?

author: MrW0lf
author_rank: Frequent Contributor
timestamp: April 12, 2017, 08:08:45 am
content: If youre afraid that might burn it do not suggest maxing out your budget!I'd go for either Owon VDS1022I(isolated version!), but simplistic software, no decoders AFAIK.Or Pico 2204A, which is not isolated, but cheap and good for learning (advanced software w decoders, same as with high-$ models).And as with all non-isolated USB scopes - make sure you use USB hub, it will probably go first and save PC.If still decide to go for AD2. Make sure you learn real well how grounding works (different w and w/o BNC board), and what effect all the jumpers have on BNC board.BTW if you go for Pico or AD2 could try this for isolation:https://www.olimex.com/Products/USB-Modules/USB-ISO/It may cripple USB bandwidth but add some safety margin.I have both Pico similar to 2204A, AD2 and some Olimex USB-modules. Could check if it still works.And as always, watch the classic:

author: MrW0lf
author_rank: Frequent Contributor
timestamp: April 12, 2017, 05:29:56 pm
content: Tested Olimex USB 1.1 isolatoron 2010my Pico 2205 and AD2. Used additional 12V supply for isolator, do not recommend using standalone - will get very hot because internal converter is working hard.Results:Pico - normal mode quite usable, ETS and DPO modes noticeably slower. In DPO mode wfm/s dropped about 30 times.AD2 - noticeably slower, but usable.So if if working on something nasty, why not. Slow but safe. Would not recommend for low voltage work.

author: Ronny
author_rank: Contributor
timestamp: April 14, 2017, 12:41:39 am
content: Quote from: MrW0lf on April 12, 2017, 05:29:56 pmThis is an European site, would you recommend one of the isolators they sell at Amazon?https://www.amazon.com/s/ref=nb_sb_noss?url=search-alias%3Daps&field-keywords=usb+isolator

author: Smokey
author_rank: Super Contributor
timestamp: April 14, 2017, 01:19:47 am
content: Sorry for being "that guy" but if you are serious about this whole EE thing, think of your gear as an investment and get stuff you aren't going to outgrow quickly.Analog Discovery as your only piece of equipment is a giant compromise on all fronts. It's fine if you have have a specific requirement that you know it will meet, but you will eventually either damage it or go crazy using it as your one and only swiss army knife lab bench and then you are out that money when you could have started building a real set of gear. I can't deal with the 0.1in header octopus monster wire connections either.PS.. take advantage of the school labs. That's what you are paying them for

author: rstofer
author_rank: Super Contributor
timestamp: April 14, 2017, 01:47:15 am
content: Quote from: Smokey on April 14, 2017, 01:19:47 amThe octopus wires are for the logic analyzer/digital functions and seem entirely appropriate. The scope and AWG can be brought out to BNC connections and probably should be as that opens up the use of a 10x scope probeEven with a bench full of conventional tools, the AD is still my go-to tool for things like sending an SPI packet to the STM32F4 I am working on. Or even receiving back the UART echo.Sure, I can program an Arduino to send the packet but the AD offers so much more with a 27" display.

author: mtdoc
author_rank: Super Contributor
timestamp: April 14, 2017, 03:55:50 am
content: Quote from: Ronny on April 12, 2017, 12:25:01 amDon't by the probes from Digilent. Get a pair of p6100 probes for $10 from ebay.It's 20 dollars for the BNC adapter which is well worth it and eliminates the need to use the small wires when using the scope. So the total would be $209.Yes, definitely worth it.

author: ebastler
author_rank: Super Contributor
timestamp: April 14, 2017, 05:05:28 am
content: Quote from: MrW0lf on April 12, 2017, 05:29:56 pmThank you for pointing towards the USB isolator; I was not aware of these devices. The manufacturer's information about the speed rating is somewhat contradictory: It says "USB 2.0 compliant", but then again "Works with USB 1.1 Full Speed devices with data rate up to 12 Mbps". Given your test summary, I assume that 12 Mbps is always the maximum transfer rate, also on USB 2.0?Have you done a teardown by any chance, to see whether the layout and components can plausibly provide the claimed 1000V isolation? If so, I'd much appreciate a photograph! (Rather a "cut-up" than a "tear-down" for the Olimex device...)

author: MrW0lf
author_rank: Frequent Contributor
timestamp: April 14, 2017, 08:58:56 am
content: Quote from: mtdoc on April 14, 2017, 03:55:50 am+1 They are garbage, do not expect much over 10MHz with originals w/o distortion. Connected good 150MHz probes and much better!Quote from: ebastler on April 14, 2017, 05:05:28 amBoth USB 1.1 and 2.0 support 12Mbps and it's indeed maximum rate. I mostly assume USB 2.0 as 480Mbps so better refer to it as 1.1 device to avoid confusion.Did cut puppy open in isolator thread.ADUM4160 it is.AFAIK Owon VDS1022I is also with only 12Mbit isolator so offers no speed advantage over Pico or AD2 tuned with USB-ISO or similar. However with VDS1022I isolator is hardwired, and consequently cannot get 480Mbps unlike with other two when isolation not needed.

author: tszaboo
author_rank: Super Contributor
timestamp: April 14, 2017, 09:11:01 am
content: If you are undergrad, dont buy test gear. The university will have better equipped lab, and I'm quite sure, even the dormitory will have a club. Our club had all the equipment you could ask for. You get to meet people with the same hobby, learn a lot, joint projects etc.

author: Gyro
author_rank: Super Contributor
timestamp: April 14, 2017, 09:17:16 am
content: Quote from: ebastler on April 14, 2017, 05:05:28 amThat one depends on how much processing is included in the USB 'head end'. There is a range of implementation choices, eg, the likes of Hantek are just basic streamers which must rely on high speed 480Mbps USB bandwidth to stream all of the ADC samples to the PC. The Owon does most of it's processing and buffering in the unit, so only needs to pass display data to the PC at whatever screen update rate is required, this is easily accomplished within USB full speed 12Mbps limits.I have absolutely no idea which approach (or combination of approaches) the Pico, or the Diglent use in managing their data processing and USB transfer.

author: Howardlong
author_rank: Super Contributor
timestamp: April 14, 2017, 09:22:37 am
content: The Analog Discovery 1 or 2 would be my choice as well, and, as others have said, the BNC board plus a pair of probes off Amazon.I use mine quite extensively when travelling. Despite its limitations, it is a genuinely useful tool. The UI is one of its best features, an area so many other USB scopes fail in. Its biggest downside is its bandwidth, and although the BNC board+probes improves that facet dramatically, it's can still be a limitation depending on your application.Occasionally I use it on the bench too because of it digitial signal generation capability.FWIW, I did a video some months ago comparing the AD 1 and 2. Practically speaking there's no difference in performance and featured other than the variable power supply on the 2 (1 has a fixed power supply). I happen to find the form factor and packaging of the 1 to be slightly more convenient when travelling.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: April 14, 2017, 09:29:47 am
content: Quote from: Gyro on April 14, 2017, 09:17:16 amIt seems that Digilent uses "brute force" approach, and suffers more heavily at 12Mbps (but still usable). With Pico there are about million different task-oriented modes, some seem to operate like "brute force" on Digilent, some are more clever. But wild differences even within 2000 series. SDK streaming rates range from 1MSa/s to 31MSa/s. Cannot exclude that current 1MSa/s models are 12Mbps only anyway. My old 2205 should be 480Mbps according to spec "USB 2.0 hi-speed (full-speed compatible)".BTW - any idea what wfm/s Owon offers? From my somevery randomtests:AD2 (480Mbps) all processing OFF, 200ns/div, 100MSa/s~50wfm/s 0% misses with edge trigger~100wfm/s no triggerPico 2205 (480Mbps), DPO mode, 50ns/div, 200MSa/s1200wfm/sPico 2205 (12Mbps), DPO mode, 50ns/div, 200MSa/s40wfm/sWhile new Pico 2408B tops at ~110,000wfm/s in DPO/Fast mode (do not remember timebase).Sometimes will try to investigate this in proper manner.

author: Gyro
author_rank: Super Contributor
timestamp: April 14, 2017, 10:56:05 am
content: Quote from: MrW0lf on April 14, 2017, 09:29:47 amThat's a shame, I was hoping it had more brains under the hood.QuoteWell they have been in the business longer than anyone else - their first product was brute force over parallel port (100ksps).QuoteI'm afraid not (other than it apearing fast enough in practice), it's not a figure they specify. There's a bit of discussion in the VDS1022i teardown thread.https://www.eevblog.com/forum/testgear/owon-vds1022i-quick-teardown-(versus-the-hantek-6022be)/I'm not sure what speed it can manage over its SCPI interface either, although Ultrawipf looks to have been doing some experiments on it recently.

author: MrW0lf
author_rank: Frequent Contributor
timestamp: April 14, 2017, 11:56:48 am
content: Testing for wfm/s quite simple with signalgen that has burst mode (see if all edges get caught to segmented mem) or rising+falling trigger pwm technique. Maybe Owon/AD2 owners try look at this deeper. I'm currently on the run.

author: Ronny
author_rank: Contributor
timestamp: April 15, 2017, 02:24:07 pm
content: Okay folks,After reading through this thread I notice 2 kinds of comments:1 - Yeah go and buy it2 - Use university lab / build your own labPeople on number 2 forgot one detail, I am an exchange student, to be specific, from Brazil! So nah, building a lab in my home would cost me the equivalent of one semester of tuition. The university has 2 kinds of labs, the one you can just go and use, it is full of bad scopes, and the nice ones, which are a pain to get in to.So for me the choice was obvious, just ordered the AD2 + BNC board. I also happened to see a pickit 3 there, it was the cheapest place to buy it, I was going to buy it too so I threw it in there making a total (with shipping) of $250Whatever, it is done now haha.So, I followed your advice and did not order the probes from Digilent. Are any of those here good?https://www.amazon.com/RioRand-Oscilloscope-Clip-Probes-Accessory/dp/B0030KWM30/ref=sr_1_1?ie=UTF8&qid=1492252259&sr=8-1&keywords=oscilloscope+probeshttps://www.amazon.com/Hantek-200MHz-Oscilloscope-Switchable-Accessory/dp/B005O0V01E/ref=sr_1_4?ie=UTF8&qid=1492252259&sr=8-4&keywords=oscilloscope+probesAnd lastly, I am starting to wonder if USB isolation is really needed, I will use it with a laptop running of batteries. If you still think it is needed, can you recommend me one from US Amazon? I don't understand anything about USB isolators.Thank you very much guys.

author: rstofer
author_rank: Super Contributor
timestamp: April 15, 2017, 02:41:09 pm
content: Re: USB isolators.I plug my AD into a powered USB hub such that the power comes from a wall wart, not the PC power supply. On the AD1, the power supply outputs come from the PC via the USB cable. On the AD2, you can use an external wall wart and you might want to look into that. It not only saves on the PC, it increases the current capability of the power supplies.The reason for isolation is the off chance that you make a mistake in grounding and the PC ground gets used as a path for some really high currents. This simply shouldn't happen.First, know what you are probing. Second, keep your probe on 10x - always. Yes, that limits the very low end of voltage measurements but it improves frequency response (reduced circuit loading). In the last 13 years of messing around I can't remember EVER using 1x. Third, pay attention to the voltage limits of the device. There is excellent documentation at Digilent.If you simply have to get involved in high voltage (higher than 12V in my view) and high current (more than a couple of amps), use the school's lab. Why do you suppose the scopes don't work? High voltage, high current, low thinking.Treat it gently and I think it will last a very long time. You might check that the digital IO is all 5V tolerant. Otherwise, the AD2 would prefer to talk to 3.3V logic. Some Arduinos are 3.3V and some are 5V. Make sure you know what you are probing!I would also suggest that you disconnect the AD from stuff that is powered when it isn't. In fact, put it back in the box when its not in use. Treat it with respect...I guarantee you will be impressed!ETA: Don't loan it out! By now you probably understand why the school's scopes are junk! Same guy...

author: Ronny
author_rank: Contributor
timestamp: April 15, 2017, 02:55:44 pm
content: Quote from: rstofer on April 15, 2017, 02:41:09 pmOne of those?https://www.amazon.com/Protronix-Port-USB-Power-Adapter/dp/B00REX6DRK/ref=sr_1_7?s=pc&ie=UTF8&qid=1492267504&sr=1-7&keywords=powered+usb+hubIf that protects my laptop I am going to buy it

author: rstofer
author_rank: Super Contributor
timestamp: April 15, 2017, 03:57:40 pm
content: The USB hub looks like a much better device than mine - notably, it does USB 3.0That helps cover the problem of overcurrent but it won't do anything to prevent a gigantic ground current travelling through the USB cable into the PC chassis and out the power cord to ground. That's why a lot of people run their PC on battery - it removes the ground path.I haven't done that. Maybe I should but, frankly, I have never used my AD on anything over a few volts. It just hasn't come up! My main power supply has current limiting (and the AD has severe current limiting, especially when powered only through the USB port) so I don't expect to see a lot of current coming down the ground wire.Do you expect to do a lot of mains work or perhaps mess around with switching mode power supplies? I wouldn't do that with an AD even though it is definitely workable. You just need to watch Dave's video on how not to destroy a scope.Pay attention to this: When you run the AD with flyleads, the scope channels are floating. You need to hook up both leads for each channel although you may often ground the striped wire (you'll see what I'm talking about), or you can take a differential measurement across a resistor, for example. Nevertheless, there is no ground reference even though one of the black wires probably needs to be connect to the DUT ground. RTFM re: ground reference.However: When you use the BNC adapter, the shell of all 4 BNC connectors ARE connected to ground - just like the ground lead on a real scope or the BNC on a signal generator. All of a sudden, you have lost the differential signaling capability that was provided by the fly leads. The fly leads had a common mode limit (voltage above ground) but the inputs were truly differential.I encourage you to read everything you can at the Digilent site. Maybe watch the videos... The AD is a fantastic tool but it's usage may not be self-evident.But truly differential inputs, how cool is that? Sometimes you want to measure the voltage drop across a component that isn't grounded. Yes, you will have to remove the BNC adapter and use the flyleads but, when you really need to do this, the AD is a nice way to get it done.

author: Ronny
author_rank: Contributor
timestamp: April 21, 2017, 06:43:43 am
content: Quote from: rstofer on April 15, 2017, 03:57:40 pmI was about to order the HUB then I notice something. I intend to used it with a laptop running out of batteries, this way I can't close the ground loop. When a powered hub is connected, my AD2 will have a path to ground in it, closing the ground loop.It seems that it is much safer to use it without the powered hub, perhaps just a normal hub.I started to look into USB isolators, the only one in Amazon with a reasonable price is this one:https://www.amazon.com/SMAKN-Isolator-Digital-Isolation-Industrial/dp/B00XXPO4UG/ref=sr_1_1?ie=UTF8&qid=1492571592&sr=8-1&keywords=usb+isolatorBut it seems to be extremely slow. The fast ones are extremely expensive.It really seems that the best option for me is to run it off a laptop running out of batteries and have a simple, non-powered, HUB as a "spike shield".What do you guys think?ps. My AD2 has arrived, looking good, I am still waiting for the probes tough. Is there any way to test it without any lab equipment? I only have the stuff in my dorm, otherwise I will need to get access to the lab (I don't know how to do this yet, since I am an exchange student). I don't wanna discover a problem in it once I am back in Brazil, where, most likely, there will be no warranty.Thanks!

author: mtdoc
author_rank: Super Contributor
timestamp: April 21, 2017, 07:47:00 am
content: Quote from: Ronny on April 21, 2017, 06:43:43 amKeeping in mind the issues pointed out by rstofer, in almost all circumstances a hub is unneeded and you're right, the nice thing about using the AD with a laptop running off of battery is that you have a floating scope. A grounded usb hub would defeat that.QuoteYou can loop the wavegen output into the scope and play with those and I believe you can loop the "patterns" output into the logic analyzer and play with those.

author: rstofer
author_rank: Super Contributor
timestamp: April 21, 2017, 04:26:57 pm
content: Quote from: mtdoc on April 21, 2017, 07:47:00 amYes, you can do both of these and it can be good practice using the UI.Grab a resistor and capacitor (1k 0.1 ufd? 3 dB down at 1.5 kHz) and build a low pass filter. Here's where the floating nature of the AD inputs comes into practice: Use the signal generator to send a 1V p-p input, connect one scope channel across the resistor (floating measurement of current) and the other channel across the capacitor to measure voltage. You can run through a bunch of frequencies and watch the output. You could also take Ch 1 off of the resistor and put it across the input.Be aware: You can't float the scope inputs when you use the BNC adapter! The shields are grounded!Better yet: Use the Network gadget to sweep a range of frequencies and create a Bode' plot of phase and magnitude. There's not an EE student alive who wouldn't appreciate the convenience of this tool!