Computing stuff tied to the physical world

Getting an oscilloscope – part 2

In Hardware on Dec 21, 2011 at 00:01

This post continues where yesterday’s post leaves off, w.r.t. my adventures with oscilloscopes.

Last October, I decided to get a “real” scope. There were plenty of experiments (ongoing and planned), which would justify getting a new instrument for. Besides, Dave Jones’s review and teardown of in particular the Agilent InfiniiVision 3000 X series scopes got me completely drooling, while at the same time knowing I’d never be able to afford (let alone justify) buying such a high-end (for me!) oscilloscope.

The most popular unit by far probably, is the Rigol 1052E and its cousin the 1052D with logic analyzer. The former is called a “DSO” (Digital Storage Oscilloscope), while the latter is a more recent trend called the “MSO” (Mixed Signal Oscilloscope). The market price for these two seems to be around €400 and €900, respectively.

MSO’s are more pricey than DSO’s, and in a way it’s not easy to justify the price difference, particularly if you consider that USB-connected Logic Analyzers such as the ZeroPlus and Openbench Logic Sniffer can be had for a fraction of that price difference. My main reason for exploring MSO’s can be summarized in one word: knobs.

But before I explain, let me describe the Rigol scope and how it worked out for me.

As it so happened, a good friend was willing to lend me his Rigol DS5062CA, which appears to be the predecessor of the DS1052E. It’s very similar, in looks and in functionality:

DSC 3557

The specs of this scope are actually really good: 60 MHz bandwidth and a whopping 1 GSa/s sample rate. This means you really will get more than enough samples to get a very accurate view of a 60 MHz sine wave on screen, and probably also of a 5 .. 10 MHz square wave.

If you’ve been following this weblog in October and November, then you’ll have seen dozens of blue screen shots in the various posts, all taken from this Rigol scope (using a camera, as this unit has no front-side USB).

Since I really wanted to learn as much as I could about a scope like this, I spent a lot of time exploring all its features, including signal filtering, trigger delays, zooming in, measurements, cursors, maths, all the way to FFT. My first conclusion has to be that there is an incredible amount of functionality in such an instrument. This little unit is a perfect example of what sets a DSO apart from classical analog scopes. It’s a different ball game.

But the second unexpected outcome of this learning process, is that it convinced me completely that “knobs” are dramatically more convenient than any computer-based emulation using keyboard and mouse. Within a few weeks, motor memory sets in: you intuitively push the right buttons and turn the right knobs, while analyzing a signal and looking for the best way to visualize it. You can keep your eyes on the screen and on the circuit, while resting one hand on the controls and adjusting things. I’ll never go back to a USB-connected solution.

So the search was on – a scope, preferably with a built-in logic analyzer.

I had already figured out two things: 1) scope prices are unbounded, and 2) I’ll buy one once, and never again. This insight was an agonizing one: I knew I was going to spend way more money than I was comfortable with (for both reasons #1 and #2) and I also knew I’d be stuck with my choice forever, for better or for worse.

I’ll spare you all my deliberations. Everyone will attach a different weight to different aspects. In my case, I did want a “better than 320×240 display” and a bandwidth of ≥ 100 MHz, to cater for (vague) future needs.

As already documented on this weblog, I ended up going for the Hameg HMO722 .. HMO2024 series, now produced by Rohde & Schwarz. The bandwidths run from 70 to 200 MHz, as 2- or 4-channel units. Here’s the HMO722, on loan from R&S until my unit arrives:

DSC 2819

It’s interesting how the controls are organized slightly differently from the Rigol, and how relatively long it took me (already!) to re-learn and re-internalize the placement and menu structure. As with a photo camera, you really have to go in the deep end and completely familiarize yourself with all the different corners of the equipment to the point that – after that – you can fully focus on the experiment, the circuit, and its signals.

My conclusion? I’m very happy with this choice, and I’m not saying this to mask any form of buyer’s remorse – there is none. I ended up going for the high-end model: 200 MHz, 4-channel. And I’d do it again tomorrow.

So what would you do, if you’re considering getting a scope? Here are my – unsolicited – suggestions:

  • budget €100 – don’t get anything and don’t worry too much – you can have lots if fun without one
  • budget €250 – get something like a DSO-2090: 2-channel, very decent software – or check out this list
  • budget €400 – get the Rigol DS1052E, it’s popular and it’ll give you the most bang for the buck, IMO
  • budget €900 – get either a Rigol DS1052D, or a DS1102E w/ separate logic analyzer (such as the OLS)
  • budget €1700 – get the Hameg HMO724, superb features, can also act as 4-channel logic analyzer
  • budget €2600 – get the Hameg HMO2022 w/ options, or the HMO2024 (which is what I chose)
  • budget €4000 – don’t despair, there’s one just right for you too (there are no doubt newer lists)
  • budget €7000 – go for it, get that 4-channel 350+ MHz Agilent 3000-X series MSO, with lots of options

If I had to pare the list down further, I’d make it a choice between the Rigol DS1052E and the Hameg HMO724.

Stay tuned for the last part of this series, tomorrow.

  1. Have you seen the Rigol DS1052E hack? Turns the 50Hz model into its bigger 100Mhz brother –

    That should increase its bang for buck rating even more :-)

    • Yep – just be careful with which exact model you have. And what if it’s a downgraded 100 MHz which didn’t meet specs? Lots of scopes probably have the same internals, btw – same as with inkjet printers in the 90’s.

      See also this and this episode on Dave Jones’ EEVBlog.

    • Oh no, it’s that’s squeaky Australian again!

      Yes, you are correct to add a disclaimer. As with any hack it may not work, or it may go badly wrong, so proceed with caution… I’ve very tempted though.

  2. Hmm, seems like you really missed a project back in the day. You should have made knobs with a USB interface, to control your DSO with ;-)

    • Heh… I thought of that (will probably do the knob thing one day – wirelessly?). But there’s really much more to it than that… it’s how everything works together (and of course with a high-priced instrument, it’s also the specs of the whole setup). But yeah, I’ll be adding more knobs and encoders to my future projects, I expect…

  3. Congratulations on your scope decision. I have been using my Tek TDS210 at home for about a decade now, and it works fine. When we got some more modern scopes at work, I realized that having a front USB port to download screen captures to USB key is really nice!

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