A Tale of Two (Sub $100) Oscilloscopes

Hi, I’m Al, and I’m an oscilloscope-holic. Just looking around my office, I can count six oscilloscope or oscilloscope-like devices. There are more in my garage. If you count the number of scopes I’ve owned (starting with an old RCA scope with a round tube and a single vertical scale), it would be embarrassing.

On the other hand, if you are trying to corral electrons into doing useful things, a scope is a necessity. You can’t visualize what’s happening in a circuit any better than using an oscilloscope. Historically, the devices were expensive and bulky. I’ve had many Tektronix and HP scopes that stayed in one place, and you brought what you were working on to them (sometimes called a “boat anchor”). It wasn’t that long ago that one of my vintage Tek scopes had its own dedicated cart so I could wheel it to where it was needed.

These days, scopes are relatively cheap, depending on what you have in mind for performance. They are also highly portable, which is nice. In fact, it is an indication of how spoiled I’ve become that my main bench scope–a Rigol DS1104Z–weighs seven pounds, yet I still look for something smaller for quick jobs.

That’s how I came into possession of two cheap scopes I wanted to talk about. They are similar in ways but different in others. Neither are going to replace a real bench scope, but if you want something portable, or you are budget-limited, they might be worth a look.

Cheap Scopes

Before I dive into any details, you might think about how much you are willing to spend for a scope–especially if it is going to be your only one. If you are just looking to save money, my opinion is that you are better off buying a cheaper, older bench scope. With the availability of perfectly good scopes from Owon, Rigol, and others in the $300 range means older scopes can only sell for so much. Granted, if you actually need a scope with 5 GHz bandwidth, you are still going to have to spend a lot of money, but for most of us, a 50 or 100 MHz scope with a few channels is perfectly fine. A quick search on eBay turned up two nice Tektronix scopes and an Agilent for $100 on the first result page, for example. You could probably get something for even less if you shopped around.

There is a rash of very cheap scopes based on fast ARM or other processors. These are neat, but the reality is that many have low-bandwidth front ends or suffer from other issues. Some of the $15 or $20 kits are reasonable at that price, but once you get up to the $100 neighborhood, I think you should have better if you are looking for your first scope. The same goes for “soundcard” scopes (mainly an input network that feeds signals into your PC’s soundcard). Fine for a DIY project, but probably not what you want for your only scope.

The two scopes I want to look at for now are the Owon Wave Rambler and the AllSun (or, sometimes, ESun) EM125. The Owon is a small hand-held probe with a USB cable that sends data back to a PC application. The EM125 is a scope meter — it has a small display and can also work as a volt or ohm meter. It does not connect to a PC. Either instrument costs just about $100 and is easily available.

EM125

em125aThe EM125 is about the size of a mid-size digital volt meter, but while most volt meters are held in a portrait orientation, the EM125 is landscape. In fact, it looks somewhat like cheap knockoff Playstation hand-held video game.

One thing I like about the EM125 is it has a USB-chargeable battery that lasts a long time. I had an old Velleman handheld scope that used NiCads or regular cells and the first thing you had to do when you wanted to use it was either charge or replace the batteries.

The EM125’s monochrome screen isn’t going to give an iPhone any competition, but it is serviceable. The menu system isn’t totally intuitive, but it works well enough. The scope part of the instrument has a reported 25 MHz bandwidth and there is a proper connection for a scope probe. The meter section uses a standard shielded banana plug. That means that you can’t just hook a probe to a point and then read everything off the probe.

There is a nice little kick stand that holds the meter at a good angle if you want to use it and a switch to turn on the battery-draining LCD back light. I don’t like to use a scope’s auto function, but on this little meter, it is handy just to hold down the button and let it find proper settings for a given waveform.

You can set up everything manually, though. You can trigger on rising or falling edge, and set the horizontal and vertical scales. You can also set a sort of auto trigger mode along with the trigger level. The meter shows the frequency and voltage of the signal (you can select RMS, average, or peak-to-peak readings). There’s also a display for battery level and a switch to select AC or DC coupling. There is a USB port, but as far as I can tell, that is just for charging the battery. Unfortunately, there’s no probe compensation signal or other test output.

OWON Rambler

owon1The Rambler is not too different from the EM125 regarding cost or performance. It also claims a 25 Mhz bandwidth. It is USB powered, so batteries aren’t an issue. However, there’s very little to it other than a scope probe tip that is part of the device (you can’t use your own probes). There is a switch to select 1X or 10X and a multifunction trackball that reminds me of a Blackberry pearl.

You must use the Windows software to see any results. I didn’t have any luck running the software under Linux, although I didn’t go as far as to use VirtualBox. There is some very basic open source for the OWON RDS scopes, but I couldn’t get it to work with this particular device.

On the plus side, you can get some fantastically cheap Windows tablets lately (well under $50), and the scope did work with those. The software interface is a little clunky on a tablet though, so I wound up mostly using a Windows laptop. But if you need a portable solution, a tablet and the Rambler could be an answer, and the software is more capable than the EM125. Like the EM125, there’s no calibration or probe compensation signal available.

How Do They Work?

Subjectively, both of these devices feel different from using a normal oscilloscope. The EM125 is handy and has a real scope probe, but the relatively poor quality of the screen means you can’t really see the detail you probably want. The Rambler, on the other hand, gives you plenty of detail, but holding the fat probe and using the trackball takes some getting used to. It also absolutely requires a PC or tablet to be connected.

If you want to see more about these devices, see the videos below. Next time, I’m going to put both of these scopes through their paces with some simple waveforms and see how they do in a less subjective way.

Honestly, I might use the Rambler more if it supported Linux nicely. It is much more like an ordinary scope in function, if you can just get used to the feel of it and don’t mind lugging a PC around. On the other hand, the EM125 has earned a place in my go bag. Instead of a basic meter, you can carry this and get a meter and a scope (although the meter won’t measure current). Maybe the scope isn’t great, but it is better than having no scope at all.

Just remember, for about the same price you could get a traditional used scope that probably has multiple channels and a host of other features you’d really enjoy and use. Sure, it might also weigh more than your whole PC, but it would be more useful. However, either of these would make a good second scope if you have any need for portability.

42 thoughts on “A Tale of Two (Sub $100) Oscilloscopes

    1. Sounds like you’re looking for a more capable version of the Mooshimeter. For its intended use, that device is sweet. App could use some polishing, but I like what they’ve got going.

          1. Because touch screen are the worst invention ever when it comes to instrument control panels. They are acceptable for gadgets, but not for lab or industrial equipment.

            Physical buttons are simply irreplaceable in their comfort and safety of use. On the contrary, touch screens are so prone to errors, both machine errors and operating errors, that sometimes may lead to accidents in industrial environments.

            But panels with real buttons are way more expensive, and marketing is always pushing mindless fancy pantsy features, so real buttons are slowly fading out.

    2. Waveforms would suffer from being quantized at the phone screen resolution to the point small details (rinings, overshoots etc) could be almost unnoticeable. Not to mention the terrible usability.
      Math functions aside it wouldn’t stand the comparison with any $100 used analog from 30 years ago or more.

      …Though it would be cool for sure:)

      1. Modern smartphones have better screen resolutions than modern digital oscilloscopes by quite a long way. The lower-end Rigols are 320×240, higher-end scopes are 800×480 which is about the same as the lowest-end smartphones on the market.

      2. The old scopes (CRT oscilloscope) were only about +-1.5% to +-3% accuracy. If you needed accuracy then there is always a meter.

        I worked in repair for a number of years and a scope was my primary diagnostic tool.

        You use a scope differently to a meter – a meter might tell you that a secondary regulated power rail is 2% low and a scope may tell the same power rail is oscillating wildly with noise.

        Scopes have zoom so fine detail can be seen even with the limitations of quantizing.

        I looked around at these pocket scopes and there all too low a bandwidth for realistic use. The sub $100 ones I have seen are good for audio frequencies. The ones that cost the same as a CRT bench scope have a tenth of the bandwidth of the bench scope – 1 to 2 MHz.

        I will have to go make a scope with some FPGA and a SoC. I could probably get some (barely) useful results from the latest Cypress PSoC chips. For diagnostic (fault finding) purposes you don’t need a hi-res display or a high degree of accuracy. You *just* need to see the *picture*. Then if I add some fast FPGA for the ADC along with a big SRAM, I should be able to do something decent.

  1. While it is also true of other pieces of test equipment, I find the drop in price and the rise in specs of the oscilloscope over the years positively breathtaking. I don’t have much use for one anymore, but I am still insanely jealous of those that do and have such nice units to choose from.

    1. If you’re in the USA and have $100-$200 you can get yourself a *really nice* used O-Scope. They’re getting really inexpensive and there is something to be said for the quality of the electronics produced in the 80/90s.

        1. The Tektronix 465 is a warhorse. They are rugged and easy to use. I see them on Craigslist for $100 to $150 regularly. Curiously, the 2465 is a nicer scope (400MHz vs 100MHz, 4 channels vs 2, measurement cursors), but they used custom hybrids that are no longer available, so when they die, they are done. The 465 uses discrete transistors that can be crossed to currently available parts. With that said, if you can get a decent deal on a 2465, they are nice scopes.
          Low sample rate digital scopes are not worth the effort in my (snooty) opinion. Figure the useful frequency of the scope will be about 1/5 the max sample rate. The digital scopes took a while to evolve into something useful, so if you see an old one for sale, be sure to try it out and make sure it works sanely for you. By the late 1990’s HP/Agilent had figured it out. Tek took a little longer, but by about 2000 they too had some easy to use stuff around. The little THS720s and 730 battery powered scopes are nice for a portable unit, but they still bring $400 – $500 and will probably need a new battery pack ($75) to use away from the AC line.

          BobH

  2. Personally I’m really fond of picoscopes. They are highly capable with a wide range, from a simple pen design like to owon to several GHz bandwidth usb3.0 units. I personally own 2, a 10 MHz unit and a 200 Mhz unit with digital inputs. Am also considering buying a windows tablet to make them more portable.

    Oh god I sound like a salesman reading that back through. For the record I am not affiliated with them!

    1. I demoed a prototype USB 3, 4 channel, 2 Ghz,bandwidth, 450Mhz/ channel, 10 bit data logger with 800 Mpts depth and a +- 1mv to 80v frontend depth on a high end Surface Pro 3 a couple of weeks ago.

      Difficult to say no to, if they can meet their price point.

    1. One more proof that Java being multi platfrom is a myth. A protocol documentation on Github would have brought in no time the needed software written by the community.

      Agreed on USB. I wonder why they don’t use Ethernet. I’s nearly realtime, very fast, free, hugely documented and supported everywhere. Strip the unnecessary layers and you connect point to point with anything at level 2, add level 3 and you can talk in a local network to multiple devices, add more layers and it gets flow control to go on the internet. To me it’s the best option out there. Did I miss something?

      1. Quick googling and browsing repository:
        https://github.com/vuokko/libsigrok/blob/owon-vds/src/hardware/owon-vds/NOTES.txt

        Ethernet is nice but how would scope or some other thing do it? It doesn’t know if it connected to straight to windows machine when working on the field with guy computer and scope or some real network and standing on bench. USB handles both of these scenarios. Also working with lower level of communication would require changes to network settings of the PC. Again it isn’t that bad when using desktop computer but with laptop, it might become issue.

    2. I don’t mind USB so much, especially these days, but Java definitely sucks. I can’t count how many times it has let me down or caused endless hassles. The Owon would be a winner if it was supported under Linux. Is the Java source available?

  3. I have and use a Tek TDS340A scope. Really works well and can be had for about $100. I think 100MHz and 500MS/s. If you get it with the options installed you have VGA (mono), GPIB, serial, and a parallel port. You can do screen dumps to floppy or over GPIB or to a printer plotter. And it boots up fast, which is something that really annoys me about modern scopes.

  4. Years ago I bought a RadioShack ScopeProbe (ProbeScope?) on closeout it was about the size of a Logic Probe with a tiny LCD. But it has a bad solder joint or something as it will only work when held (pressed) in a certain way. PITA

  5. >Just looking around my office, I can count six oscilloscope or oscilloscope-like devices. There are more in my garage. If
    >you count the number of scopes I’ve owned (starting with an old RCA scope with a round tube and a single vertical scale),
    >it would be embarrassing.
    If you want to see lots of scopes (and other cool stuff) you should go there –> http://www.eevblog.com/forum/chat/whats-your-work-benchlab-look-like-post-some-pictures-of-your-lab/

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