Digitizing 'scope suggestions on a budget - Page 1
Forum section: electronics / beginners

author: byoungblood
author_rank: Contributor
timestamp: May 15, 2017, 04:45:20 am
content: I've dabbled in electronics for about 20 years, but it hasn't been except in the past few months that I've actually tried to sit down and actually LEARN what I'm doing outside of some very basic circuits.I've got an old-ish (probably early-90s) LG OS-9020A scope that I got for free about 10 years or so ago from a place I worked at that was clearing out a bunch of old equipment they had. Nothing wrong with it functionally, but I think I'd like some of the features of a digital scope like automatic measurements, more stable waveforms, etc.Because I may sometimes go for months without messing with much, I'm really just looking at used equipment, probably trying to stay under about $200.2 channels, 60-100MHz bandwidth are probably more than sufficient for my purposes. I've mostly just repaired things that won't power up (real simple power supply issues), have bad caps, modified a few simple audio circuits, etc., as well as some rather simple stuff with an Arduino. I'd also like to get an old 40s era antique radio up and going again, but I haven't fooled with anything with tubes since my early-20s (I'm pushing 40 now).Here's one I was looking at on eBay, but I read a couple of old threads on here that suggested that they had some issues, and Dave tore one down and mentioned that the displays were slow to update.http://www.ebay.com/itm/232323709290?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AITAnyone have any other suggestions on what to look for?

author: Muxr
author_rank: Super Contributor
timestamp: May 15, 2017, 04:52:28 am
content: People will probably tell you to save up for a Rigol 1054z or similar, but really for the price that scope you linked is not too bad, provided it's in fully functioning order.

author: P90
author_rank: Frequent Contributor
timestamp: May 15, 2017, 05:08:32 am
content: deep memory is a key feature, if you want to be able to capture and troubleshoot anything meaningful...

author: james_s
author_rank: Super Contributor
timestamp: May 15, 2017, 05:18:34 am
content: That depends on what you're trying to do. I frequently use a TDS340 since it's my "small" portable DSO. It doesn't have a lot of memory but it's a perfectly usable instrument and coming from an analog scope it has a lot of advantages. A TDS210 is older and not super powerful but it's still a capable scope. With a budget of less than $200 you can't have everything. I have seen a couple of TDS540 500MHz scopes sell for less than that but that's a very large and bulky unit compared to the TDS210. Deep memory was a rather high end feature until relatively recently, people got along without it just fine for a long time. You just have to know how to properly use the scope in order to work around the limitations and see what you want. We did plenty of meaningful troubleshooting with analog scopes having no memory at all.

author: Muxr
author_rank: Super Contributor
timestamp: May 15, 2017, 05:22:51 am
content: Quote from: james_s on May 15, 2017, 05:18:34 amThat's where I am at with this as well. Deep memory can be very helpful especially for spurious events since you can't recreate those easily. But for most stuff you can just navigate to the spot you want to take a closer look at and re-trigger on the same event usually. I like the compact size and for the price you can't ask for much more.

author: mmagin
author_rank: Frequent Contributor
timestamp: May 15, 2017, 05:43:04 am
content: I would not bother with a digital scope with less than 1Msample per channel sample memory for general purposes. I have a HP 54645A, it's ok, but don't bother with the pre-megazoom HP digital scopes for general use.

author: P90
author_rank: Frequent Contributor
timestamp: May 15, 2017, 06:40:14 am
content: many of the new Tek scopes for several hundred dollars only have a few Kpoints of memory!

author: james_s
author_rank: Super Contributor
timestamp: May 15, 2017, 08:04:51 am
content: Quote from: mmagin on May 15, 2017, 05:43:04 amWhat would you suggest for a budget of under $200 though? The VW Beetle was a crappy car by most standards, but it had one big advantage in that it was affordable. Not everyone could afford a Mercedes despite it being a far superior car. My primary scope is a TDS784C, it's a wonderful instrument, has deep memory and a 4GS/sec sample rate but it's also a beast, it takes up half the table and weighs 35 lbs. I frequently use a much less capable TDS340 simply because it's much smaller and lighter and it's still perfectly able to do the job. There's a lot of snobbery out there when it comes to scopes, but for general purpose use not everyone needs a high sample rate and tons of memory. Those features do make things simpler but if you know how to properly use the scope you can work around the deficiencies of older instruments pretty well. For someone coming from a low end analog scope, a TDS210 will open a lot of doors.

author: DTJ
author_rank: Super Contributor
timestamp: May 15, 2017, 08:08:05 am
content: Quote from: blueskull on May 15, 2017, 04:57:26 amI disagree. I regularly use my TDS_210 that I purchased new nearly 20 years ago!It works fine and is a more than capable instrument for most uses.Theres no issues with triggering them.If you can locate a second hand one for say $100-$200 I'd say buy it.Horses for courses.

author: P90
author_rank: Frequent Contributor
timestamp: May 15, 2017, 08:10:41 am
content: Quote from: james_s on May 15, 2017, 08:04:51 amI disagree. The VW was a brilliant bit of engineering and way ahead of its time. You couldn't find any other car that lasted as long. To this day, I still see them on the road occasionally, after 75+ years.

author: james_s
author_rank: Super Contributor
timestamp: May 15, 2017, 08:36:47 am
content: Perhaps that was not the best choice of comparison but let's look at this objectively. Charming as they are, the VW Beetle was grossly underpowered, especially the early ones. The engine has a habit of thrashing the main bearings due to crankshaft flex if you rev it too much. The heater is hopeless, making use in cold climates unpleasant. The cars are spartan, with only the most basic creature comforts. They are death traps in a collision, offering little in the way of safety features. I've driven one and it was a neat classic car but I would never recommend someone buy one as a daily driver, they no longer have the big advantage of being cheap. Yes they were ahead of their time in many ways when new, yes quite a few of them are still out there being used, you can still get around in one. The same could be said of an old DSO like the TDS210, there are better scopes out there if you have the budget but otherwise like the VW, it's still a capable instrument despite not being as fast or having modern features like deep meory, color screen, USB, etc.

author: Gyro
author_rank: Super Contributor
timestamp: May 15, 2017, 09:15:46 am
content: For you 'Deep memory' folks I suggest you actually go back andreadwhat the OP wants to use the scope for and his budget.@byoungblood: For simple Arduino stuff I would suggest that you suppliment your purchase with one of those cheap $10 ebay logic analysers together with Sigrok S/W to capture long data streams, decode data etc.EDIT: I think that for '40s radio dabbling, a decently engineered Tek type front-end (protection) is probably more of an asset.

author: sokoloff
author_rank: Super Contributor
timestamp: May 15, 2017, 11:34:17 am
content: Quote from: Muxr on May 15, 2017, 04:52:28 amI just got a 1054z after doing some fairly solid research for entry-level hobby scope and that is what I'd recommend. Not only is it a solid scope, I find that having popular/common equipment means that Google searches while I'm a n00b wandering around are more fruitful.On the finance side, mine was ~$375 delivered [new from TEquipment], included 4 probes, LAN and USB connectivity, 3 million+ sample/channel memory (6 after hacking), easily hacked, etc. To save the extra $175, I'd look hard at brown-bagging lunches for a month, skipping a couple dinners out, cutting out Starbucks, or similar. I'll get a lot more enjoyment out of the scope over the next 10 years than those small sacrifices. (I don't want to make light of anyone else's financial constraints, but I think many of us in the US could find $20 a week to save for something important without excessive sacrifice.)

author: P90
author_rank: Frequent Contributor
timestamp: May 15, 2017, 11:40:35 am
content: Quote from: james_s on May 15, 2017, 08:36:47 amdeath trap?Ford Pinto anyone? How many burned to death in those?Corvair POS? Decapitation in Corvettes?

author: byoungblood
author_rank: Contributor
timestamp: May 15, 2017, 01:44:22 pm
content: Thanks for the feedback everyone. My budget isn't exactly a hard one, but it is mainly a by product of my frugality and how much I think I'll use it. I could spend twice that no problem, but I'm just not sure I'd use it enough to justify the expense at the moment.It looks like if I bump my budget up slightly I could get a Rigol 1102 for around $270 or so. Are they worth that, or would I just be better off holding out for a new scope for $100 more at that point?

author: P90
author_rank: Frequent Contributor
timestamp: May 15, 2017, 01:50:47 pm
content: Quote from: byoungblood on May 15, 2017, 01:44:22 pmYou're better off with a Siglent SDS1102CML+ for a few bucks more. bigger screen, more memory.

author: rstofer
author_rank: Super Contributor
timestamp: May 15, 2017, 02:33:38 pm
content: Quote from: byoungblood on May 15, 2017, 01:44:22 pmRegardless of which scope you choose, read the manual first! You wanted measurements yet the suggested TDS210 only offers the most elementary measurements. That scope is not much better than an analog scope and I'm not even sure that is true. One nice feature, common to all DSOs I would imagine, is single shot mode. That's something you simply don't get with the common analog scope.There are probably just 2 entry level scopes most commonly recommended over in the Test Equipment forum: The brand new Siglent SDS1201X-E 200 MHz 2 Channel and the Rigol DS1054Z 100 MHz 4 Channel. The Siglent is $379 and the Rigol is $399. I have the Rigol. The thing about the Siglent is that it is brand new and has some firmware issues whereas the Rigol is a couple of years old and has gone through several upgrades. At this point, the Rigol is pretty well understood.There is no reason to go for the 2 channel (plus trigger) Rigol 1102e since the 4 channel 1054Z is just $40 more.But, back to your budget, you can get the TDS210 from eBay for about $200. It's better than nothing but it ties up money that might better be applied to a more useful scope.A 4 channel scope is really useful when you want to watch all the signals involved with the SPI protocol. It can also be done with a logic analyzer.

author: tggzzz
author_rank: Super Contributor
timestamp: May 15, 2017, 03:07:15 pm
content: Quote from: byoungblood on May 15, 2017, 04:45:20 amDon't presume digitising scopes are "more stable" than analogue scopes; the quality of the trigger circuit is very important.Some analogue scopes also have automatic measurements, e.g. Tek 24*5 series.The use case for storage scopes is for one-off events such as power supply switch on/off behaviour. Digitising storage scopes are an immense improvement on analogue storage scopes.A good rule of thumb is to debug analogue signals in the analogue domain, and digital signals in the digital domain. In practice that meansusing a scope (either analogue or digitising) to ensure "signal integrity", i.e. to ensure the analogue signals are well behaved so that the receiver can "interpret" them correctly as a digital signalonce you have a valid digital signal, flip to debugging in the digital domain using a logic analyser or printf statements or scope that can infer meaning in digital signals (a.k.a. protocol decode)My preference is to have analogue scopes with a reasonable bandwidth (>250MHz) for signal integrity, and an el-cheapo logic analyser.In your shoes, if your existing scope is adequate for your current needs, then I would consider spending money on an LA or sig gen or PSU.

author: james_s
author_rank: Super Contributor
timestamp: May 15, 2017, 03:36:18 pm
content: Quote from: P90 on May 15, 2017, 11:40:35 amNowhere have I claimed that the Pinto was a good car either. They were not as bad as the reputation makes them out to be, very few actually caught fire. Like the VW, the Pinto was engineered as a low cost compact car with good (for the era) fuel economy, certain sacrifices were made to meet that goal. The Corvair was also a compact and light weight car, also like the VW it was far ahead of its time in many ways, air cooled horizontally opposed engine alloy block engine and alloy gearbox. It was also one of the early successful examples of turbocharging available in a mass produced car. Ralph Nader latched onto them and made a lot of money selling is book but they were not as bad as the reputation suggests. The suspension was updated in later models but it was too late to save the reputation. The Corvette was a light weight fiberglass sports car, it was not particularly safe but neither was any other vehicle of the era.All of these vehicles mentioned I would consider deathtraps by modern standards and I would not be comfortable using any one of them as a daily driver. Having spent the last ~18 years rolling around in a Volvo which made their name with a focus on safety, most older/smaller cars feel rather unsafe to me. My perspective may be a bit different than most, having been rear ended by a distracted semi driver on the freeway relatively recently. I was very lucky to walk away, it could have easily been much worse. Had I been driving anything else mentioned here there is little doubt that I would not be here to comment on this thread.On a related topic, the legendary engineer Bob Pease was killed in his '69 VW Beetle on his way home from fellow legendary engineer Jim Williams' memorial service. No matter what you drive, be careful, even the best drivers are at the mercy of all the others on the road. Drunk, texting or playing with their phone, messing with the radio, you name it.

author: P90
author_rank: Frequent Contributor
timestamp: May 15, 2017, 03:47:03 pm
content: Quote from: james_s on May 15, 2017, 03:36:18 pmI've owned several Volvos. Everything else feels like a sardine can. My 240 wouldn't die.All in all, I really hate driving more and more, there are too many idiots on the roads no matter where you go...Maybe I should mention trains... since I completely derailed this thread...

author: mmagin
author_rank: Frequent Contributor
timestamp: May 15, 2017, 04:43:12 pm
content: Quote from: james_s on May 15, 2017, 08:04:51 amFWIW, looking at sold listings people regularly get working 54645A for less than $200 including the cost of shipping:http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=hp%2054645a&LH_Complete=1&LH_Sold=1&rt=nc&_trksid=p2045573.m1684Similarly for the newer generation 54622A (haven't used that one personally.)The cheapest of the used Rigols are down in that price range and much newer (DS1102E), though they have that weird long memory tradeoff to be aware of:https://www.eevblog.com/forum/testgear/rigol's-'long-memory'/msg15394/#msg15394The reason I and others were commenting about sample memory was that it's one of the more significant specifications to be aware of with a digital scope, and it's one area where modern-equivalent spec only just started to show up 20 years ago.

author: mmagin
author_rank: Frequent Contributor
timestamp: May 15, 2017, 04:46:38 pm
content: Quote from: P90 on May 15, 2017, 06:40:14 amOh my, I could hardly believe it, but it's true:http://www.tek.com/oscilloscope/tbs1000-digital-storage-oscilloscope

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2017, 04:56:28 pm
content: Deep memory is necessary for a minority of oscilloscope applications. In an oscilloscope now, it is a less expensive incomplete replacement for dual delayed sweep. Increasing integration makes large amounts of memory "free" while a dual delayed sweep always involves extra logic and design. The same integration improvements make digital triggering "free" compared to analog triggering.If you are using your oscilloscope as a logic analyser, then deep memory is more important but most DSOs are poor logic analyzers and some are terrible.Tektronix held on with short record length oscilloscopes because they were based on a different and inexpensive digitizer design which did not rely on digital memory. HP/Agilent/Keysight has a similar investment in their Megazoom technology which is an ASIC loaded with embedded SRAM. These days do to increasing integration, small manufacturers can get adequate performance with an FPGA based design which leads to long record lengths and digital triggers because that is the cheapest implementation possible.A good example of the above is the Rigol DS1000Z series. It has neither delayed sweep (delayed acquisition) nor trigger after delay despite these features being very useful whether long record lengths are present or not. These features are missing because they have significant costs in logic and design. Long memory does not completely replace these features; it is simply a cheap and incomplete alternative which is sufficient for most users.

author: rstofer
author_rank: Super Contributor
timestamp: May 15, 2017, 05:15:39 pm
content: Quote from: mmagin on May 15, 2017, 04:43:12 pmI'm not sure I follow re: a 'long memory tradeoff'.From the latest Rigol User Manual:QuoteSo, I only get 6M points/channel with 4 channels running. I think I can deal with it!

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2017, 07:30:57 pm
content: Quote from: rstofer on May 15, 2017, 05:15:39 pmAnd then you read the fine print which Rigol conveniently leaves out. It makes measurements on its 600 point display record which is shorter than the record length of Tektronix DSOs which are old enough to drink. The Rigol presents a 600 point display "window" into its 6M acquisition memory so it operates more like a DSO with a 600 point record length and 6M single shot capture capability.One of the reasons that more expensive DSOs with smaller record lengths than the Rigol are slower is that they make measurements on their much longer and higher resolution processing record. In most cases they take an 8-bit acquisition record from the digitizer, convert it to a 16-bit processing record, and then create a display record for viewing. Measurements are made on the 16-bit processing record so they take advantage of much higher resolution and bit depth than the display record including things like high resolution mode and averaging which the Rigol does not do but this also means that for the same processing power, they are slower.Despite this,the Rigol DS1000Z series is a fantastic valueand it does meet two of my must have requirements in a DSO; it has peak detection which earlier Rigol DSOs lack and it has real 1 megohm inputs. Personally I would not buy one because I have alternatives and besides its other shortcomings, it cannot make RMS noise measurements and its delay range is too limited for some things I do.

author: mmagin
author_rank: Frequent Contributor
timestamp: May 15, 2017, 08:19:37 pm
content: Quote from: David Hess on May 15, 2017, 04:56:28 pmI suppose. Do modern shallower-memory oscilloscopes avoid the problem particularly rampant in OLD digitizers like my Tek 468 had where because it only sampled 256 samples, you could get situations where with a slower sweep you could get aliasing since the sampling rate went down while the front end filtering was still at its normal bandwidth?

author: David Hess
author_rank: Super Contributor
timestamp: May 15, 2017, 09:11:37 pm
content: Quote from: mmagin on May 15, 2017, 08:19:37 pmThat has not been a problem since the 468 evolved into the 2230 and peak detection became available which is why it is on my must have list for a DSO. Peak detection is a very limited form of what DPO (digital phosphor oscilloscopes) do to produce a graded index display. If the record length is long enough, then peak detection is not needed but this comes at the expense of processing time making the display update rate slower.Incidentally, the 468 is limited to a 10 MHz analog bandwidth in storage mode because that is the analog bandwidth of its TRW ADC which was intended for video applications. The 2230 included a discrete 100 MHz sample and hold before its Sony video ADC to raise its bandwidth to 100 MHz.

author: KL27x
author_rank: Super Contributor
timestamp: May 16, 2017, 06:05:39 am
content: QuoteI dunno if maybe the law is cracking down on the import of these, or something. But I ordered one and it never arrived. FTR, I have a Seleae Logic, already, and I ordered one of these unlicensed clones for kicks. So no bother. If you are going to use an open source software, maybe make sure the clone you order doesn't say "Seleae" on it... perhaps customs is confiscating these?

author: byoungblood
author_rank: Contributor
timestamp: May 17, 2017, 02:02:07 am
content: Quote from: mmagin on May 15, 2017, 04:43:12 pmI ended up finding a Agilent 54622A for about $190 shipped to me. I think in the end I felt a bit more comfortable buying from a long established brand, and from looking around it appears to be a solid scope for my needs.

author: DTJ
author_rank: Super Contributor
timestamp: May 17, 2017, 02:19:46 am
content: Quote from: byoungblood on May 17, 2017, 02:02:07 amWell done.There's a thread on that CRO here:https://www.eevblog.com/forum/testgear/agilent-54622a-ebay-score-anything-to-be-awarewary-of/

author: james_s
author_rank: Super Contributor
timestamp: May 17, 2017, 02:44:24 am
content: That looks like a nice scope and the price is reasonable assuming it works properly. I've been tempted to pick up an older HP/Agilent DSO at some point but I might risk becoming single if I acquire any more scopes. Also being familiar with the Tektronix UI getting something else would just mean getting the hang of something different. I've got a thing for CRT based instruments.