Newbie wants to buy a cheap scope - Page 1
Forum section: electronics / beginners

author: nikola1
author_rank: Newbie
timestamp: July 02, 2017, 09:01:32 am
content: Hello everyone,I'm a third year (will be fourth) electronics student from Bulgaria.I'm writing this because I'm planning to buy some equipment so I can practise in my free time this summer. For starters, and for a low budget like mine, I was thinking of a signal generator, DC power supply and a scope. So I told one of the assistants in my university (a very knowledgeable and experienced man, who teaches mostly ''measurements in electronics'') about my plan and he told me to make my own signal generator and voltage stabilizer, and to buy some cheap, digital oscilloscope with max 60MHz bandwidth (namely no more than 200$, not a small sum in my country).I'll follow his advice about the signal generator and U stabilizer, unless you guys give some other meaningful tips. Given that, almost all of my budget will go for the scope.Now, relevant info about me, so you guys can give me some directions - 220$ max (including shipping if from the US); little experience but overall good theoretical understanding on most of the subjects so far; in mind of making all types of circuits but mainly analog. I don't really care about high bandwidth and digital vs analog, but I'd prefer a dual channel. I also don't mind buying a used one as long as you think it's worth it.So, what do you think I should buy?All answers are greatly appreciated!Kinds regards,Nikola

author: Electro Detective
author_rank: Super Contributor
timestamp: July 02, 2017, 09:33:10 am
content: "voltage stabilizer"is the electricity bad quality where you are?Welcome to EEVblog

author: fourtytwo42
author_rank: Super Contributor
timestamp: July 02, 2017, 09:54:40 am
content: Quote from: nikola1 on July 02, 2017, 09:01:32 amHi Nikola welcome to the forumYou don't say if PC based is OK or not but I have been using an Owon VDS1022I for around 18 months and very pleased with it, doesn't do everything neither is the software perfect but I have not encountered any serious shortcomings.http://www.owon.com.hk/products_info.asp?ProID=175#sthash.xnS6J1Oz.dpbsas for price seems about $130 on Ebay incl shipping.

author: phil
author_rank: Regular Contributor
timestamp: July 02, 2017, 10:34:30 am
content: Have you considered anAnalog Discovery 2? You can get them quite cheap as you are a student.You can have a scope, AWG, logic analyzer and even a basic spectrum/network analyzer in one device.Note, however, that the scope bandwidth is limited - but this might not be a problem for you if your focus is on learning and playing around with analog circuits. In fact, that is the use case where the Analog Discovery really shines.Take a look at theSoftwarethat comes with it. It has a demo mode, so you can try it even without owning the hardware.Edit: Should you buy one, do yourself a favor and also order theBNC board. That way you can use traditional scope probes and BNC cables.-phil

author: nikola1
author_rank: Newbie
timestamp: July 03, 2017, 11:17:39 am
content: Thanks for your answers guys.For now, the Analog Discovery 2 seems like a very good choice. It gives me all I need, but as I shared with a few friends of mine, some say that it's not a viable replacement for an oscilloscope, mainly because of the low sample rate of 100 megs/sec. Somewhere I heard that the sample rate needs to be at least 10x the max frequency (30MHz) so.... The other thing - in power supply mode it gives only +- 5V.Aside from that, I think it's very much worth it. I'll gather some more feedback about it and if I decide not to buy, I'll probably stick with a PC based scope.Regards,Nikola

author: lacek
author_rank: Regular Contributor
timestamp: July 03, 2017, 11:50:02 am
content: Quote from: nikola1 on July 02, 2017, 09:01:32 amOf you want to spend at most $220, then you should definitely NOT ship from the US. It will eat 25-50% of your budget. Better ship from Bulgaria, Hungary, Poland, or ever Germany. Shipping from US should be a last resort.

author: welpester
author_rank: Contributor
timestamp: July 03, 2017, 04:36:03 pm
content: How much it costs to send scope from finland to bulgaria?-welpesteredit: I answer to my self: About 50 euros

author: phil
author_rank: Regular Contributor
timestamp: July 03, 2017, 04:55:13 pm
content: Quote from: nikola1 on July 03, 2017, 11:17:39 amThe sample rate is sufficient for its bandwidth. f_s is about 3.3*f_(-3db) on the AD2. For reference, a hacked 100MHz rigol 1054Z with all 4 channels active only has a ratio of ~2.5 - and it still works!QuoteThat is incorrect. You *need* to sample at least twice as fast as the highest frequency present in your signal. In practice, 10xBW is an often recommended thing because anti-alias filters are generally not very steep. So having a higher sample rate than needed in theory will greatly reduce aliasing due to non-perfect filters. Also, while two samples are enough in theory, it is very hard to see a signal that has only 2-3 samples/period. 10 samples/period is a lot easier on the eyes.All of this will only matter if you have a signal with significant components >50MHz after the anti-alias filter.I use my AD for most things I do - mainly because I am lazy and do not want to walk to the other bench when testing µC-based stuff. You can go a *long* way with the AD alone.But your friends are right: The AD is no replacement for a proper bench scope. But a proper bench scope will cost you way more than 220€ if you want it to be better than the AD. For its (academic) price it is a no-brainer for me. Used analog scopes offer a lot of bandwidth per €. Might be worth looking into if you find the AD to be too limited in the future.Note: I strongly recommend getting a digital scope first, even if it has limited bandwidth.The power supply is more or less a gimmick intended to be used with low power analog circuits on a bread board. You will need an actual bench psu for your projects.-phil

author: welpester
author_rank: Contributor
timestamp: July 03, 2017, 05:31:59 pm
content: Is it MUST have digital? Buy an analog scope and sample rate would not be an issue?-welpester

author: willbanks
author_rank: Contributor
timestamp: July 04, 2017, 07:17:30 am
content: you can get a cheap analog scope off ebay for less than 100 bucks. i got a 20mhz analog scope for $90, free shipping.digital scope under $220 tho, youd need to get a used one more than likely. or you could go for a USB scope.

author: NivagSwerdna
author_rank: Super Contributor
timestamp: July 04, 2017, 12:42:06 pm
content: IMHO the Analog Discovery 2 might be a very good choice.I bought myself a Rigol 1052E scope after decades of not thinking I could afford one for my hobby and it works really well but after a few years I am slowly outgrowing it and have scope envy for the more modern 4-channel Rigols which have in built SPI decoding etc. A DS1054Z is now really really good value but above your (and mine) current budget.If this is a sort of once in a lifetime purchase...It's really important to know what you really need, might be worth using something cheap and cheerful that just works whilst you keep saving!

author: Electro Fan
author_rank: Super Contributor
timestamp: July 04, 2017, 04:45:06 pm
content: Quote from: nikola1 on July 02, 2017, 09:01:32 amYou are getting sincere and insightful advice here and hopefully it will be helpful to your decision.When we look at your choices it seems to be:USB vs. standaloneanalog vs. digitalnew vs. usedAlong with those possibilities other factors are your budget, and that you are located in a market where a large selection of scopes might not be abundantly available. (In your budget criteria be sure to include shipping, taxes, and probes as well as the scope. If a scope is used, you either have to be sure it's working or factor in possible repairs.)With all the advice in mind, I think you should search for the best 3-5 scopes that you can find that meet the criteria most important to you. Let us know what the top 3-5 turn out to be and people here will help you sort through the tradeoffs on those.Having said all that, I'd but the Analog Discovery on the list (it's pretty close to fitting your budget and it will provide some logic analyzer and other functions), and I'd put a Rigol 1054Z on the list - if nothing else as a reference point for what might be possible if your budget can stretch. Then I'd add the next three best scopes you can find and compare and contrast all the choices.I think it's good to first collect data, then analyze the data, and then stand back and evaluate what the data is telling you. (And part of the fun and learning process with test equipment is shopping for the equipment.)Good luck on the scope and most importantly on your EE journey!!

author: Kinvert
author_rank: Newbie
timestamp: July 05, 2017, 02:28:55 am
content: I started with a Parallax USB Scope.This is a new account so I'm not sure if I should link to it.Now I have a Rigol 1054Z. I'm super happy with it. I got it for I think $385.It was Dave's video that sold me on the scope.

author: nikola1
author_rank: Newbie
timestamp: July 07, 2017, 10:09:15 am
content: Hello everyone,Looks like I won't be buying anything in the near month. On the other hand - my budget will increase more than double in a month, and triple in the next two months since I got a job.Taking that into consideration, I don't believe you would still recommend me AD2 or USB scopes. I think that I should start looking for something with a more long-term use.I also might study acommuncations magister's degree, but I have interest in that only because I love math. That means that I havevery little idea of what kind of signals I'd be looking at, and what kind of parameters would be important for the scope.So my question is more about the parameters, rather than what I can fit in a certain budget, since I really don't know how much I'd be willing to spend at this time?!Thanks for your time.Best Regards,Nikola

author: Brumby
author_rank: Unknown
timestamp: July 07, 2017, 05:57:11 pm
content: From what many have said here (and I only speak from observation, not experience) the Rigol DS1054Z has been mentioned (more than once) with positive comment in being good bang-for-buck.If you have an income now, I would suggest you look around for a good deal on this scope and then set that as your target.

author: tggzzz
author_rank: Super Contributor
timestamp: July 07, 2017, 06:35:42 pm
content: You haven't mentionedwhyyou think you need a 60MHz scope. If there isn't a solid "use-case" requirement, then seriously consider the Analog Discovery with student discount since it is aremarkablyuseful piece of kit.You also get two arbitrary waveform generators (often more useful than a sig gen, e.g. think of IQ modulation), software to enable the AD to be a reasonable spectrum analyser (the 14bit ADC is important for that,muchbetter than the 8-bit ADC in low-end scopes), a network analyser (useful to see frequency response of filters/amplifiers etc), and control-plane analyser.The 100MS/s digital pattern generator and logic analyser is very useful for doing simple digital control and analysis.When choosing the bandwidth of a scope to be used to inspect digital signals, bear in mind that the required analogue front-end bandwidth doesnotdepend on the signal's frequency/period. The rule of thumb for the required bandwidth is that BW >0.35/tr, where tr is the transition time. So, start by determining the transition time of logic families that you might use, and use that to determine the scope's bandwidth. You might be unpleasantly surprised.

author: alm
author_rank: Super Contributor
timestamp: July 07, 2017, 07:07:26 pm
content: 100% agree that for digital signals, transition time is the important factor to consider. An SPI signal with a 4 MHz clock sent from an FPGA may still have some very fast edges. But 0.35/tr is not enough in my opinion. That means the scope will make a step with a 1 ns transition time appear as having a transition time of 1.4 ns.This appnotesuggests a bandwidth of 1.4 * 0.35 / tr for reasonable signal fidelity and 1.6 * 0.35 / tr for good signal fidelity. And that is with scopes with a better pulse response than most entry level scopes (semi-brick wall rather than Guassian input filter).

author: tggzzz
author_rank: Super Contributor
timestamp: July 07, 2017, 08:09:12 pm
content: Quote from: alm on July 07, 2017, 07:07:26 pmI did write ">"

author: Electro Detective
author_rank: Super Contributor
timestamp: July 07, 2017, 11:49:23 pm
content: Quote from: nikola1 on July 02, 2017, 09:01:32 amnikola, some explanation on theseitemsplease

author: orin
author_rank: Frequent Contributor
timestamp: July 08, 2017, 05:37:00 am
content: Quote from: nikola1 on July 07, 2017, 10:09:15 amIf your budget triples, then I'd definitely say go for the Rigol DS1054Z. I have one that's not been hacked and it's the go to 'scope. Depending on how good a deal you can get, you could also get the Analog Discovery. I got the original version on a student discount and it's a nice piece of kit, though I've mostly used its digital features for monitoring serial communications (both from standard serial ports and the proprietary serial communication in my 3455A DVM).

author: ebastler
author_rank: Super Contributor
timestamp: July 08, 2017, 06:10:16 am
content: Quote from: Electro Detective on July 07, 2017, 11:49:23 pmSeems clear enough when you read the complete OP:Quote from: nikola1 on July 02, 2017, 09:01:32 am

author: Electro Detective
author_rank: Super Contributor
timestamp: July 08, 2017, 09:24:42 am
content: I've read the OPs 3 posts x 3 times, I don't see itShould I change my browser language settings?

author: ebastler
author_rank: Super Contributor
timestamp: July 08, 2017, 10:33:24 am
content: Quote from: Electro Detective on July 08, 2017, 09:24:42 amHave you tried a full-text search on the page for the line I quoted?In his very first post, in the first larger paragraph, the OP explains that he is thinking about getting a signal generator, DC power supply and a scope. A colleague has recommended to home-build the power supply (aka "voltage stabilizer") and signal generator, and now he is looking for recommendations on a scope to buy.

author: Electro Detective
author_rank: Super Contributor
timestamp: July 08, 2017, 11:26:17 am
content: ebastler, here is a copy paste of OP below, I have refreshed the page tooI can post a screenshot too if anyone suspects I'm on medicationI'm rolling with your advice that it is a DC power supply he's after and wish him best of luck scoring some good gear cheapQuote from: nikola1 on July 02, 2017, 09:01:32 am