Computing stuff tied to the physical world

My scope story – conclusion

In Hardware on Dec 22, 2011 at 00:01

As it so happens, my scope finally arrived – and was immediately given a central place on the JeeLabs workbench:

DSC 2823

It’s phenomenal. You’ve seen plenty of analog signal traces on this weblog recently, but this one includes a logic analyzer (up to 11 channels) and serial protocol decoding + triggering. Here’s an example with bi-directional SPI:


(these screenshots are slightly fuzzier than the real thing, because I had to resize the images to fit this weblog)

Light blue is the bus decoding, yellow is the analog SPI clock (with lots of over- and under-shoot), and purple is for the logic analyzer POD. Small gotcha: on a 4-channel scope, it’s either analog channel 3, or the 8-wide logic probe – never both at the same time. But on the plus side: if you only use 2 analog channels, then the scope can re-purpose the unused channels to double its max sample rate to 2 GSa/s, and its memory depth to 2 MB each.

That first photo shows the same SPI clock, BTW – it’s what 8 MHz on jumper wires + a breadboard looks like!

As it turns out, I ran into two problems while pushing the HMO722 unit loaned to me by Rohde & Schwarz. One of them was a mis-interpretation of the screen display on my side, while the other one uncovered a limitation of (only) the HMO722. In both cases, the support from R&S was very impressive: quick, knowledgeable, and best of all… effective. In this day and age, that’s exceptional – and laudable.

Here’s another capture, triggering in RS232 / UART mode on the character 0x1D, as decoded at 115.2 Kbaud on the TX line. You can see a small sketch upload (green) and the beginning of the verification read-back (yellow):


I’ve not seen this feature in low-end logic analyzers yet. It’s probably a separate FPGA, able to decode various protocols to generate the desired trigger signal, and – being an MSO – it also ties into analog acquisition.

Note that this can be done without logic probe. It was enabled here (the two purple lines) but it’s not essential, since serial protocol decoding + pattern-based triggering can also be performed with just the analog channels. The serial data single-shot storage limit is around 2.5 Kbyte (all data is sampled and stored as a bit stream).

One more thing I really love about this scope: it’s totally quiet (thank you Hameg, for following Apple’s lead!).

I can only repeat: this HMO series is the most modern in its class IMO and has an excellent price / performance ratio, with features matching some Tektronix and Agilent scopes at twice the price. If you don’t want to settle for a USB scope or one of the Rigol’s, then get the Hameg HMO724 (or one of the others, with a higher b/w front-end).

A scope is not for everyone, of course. And this one even less so, no doubt. Keep in mind that the landscape will be completely different again two years from now. So if you don’t plan to use it much, better hold on to your cash.

But if you do need a scope now, then I hope these last few posts can help you make up your mind…

PS. A comparison in German between the Hameg and Agilent scopes can be found here (written by Hameg).

  1. Forget the scope… Cheers for the nice netbook next to it (I’ve got the same).

    Now that you’ve got this scope you probably notice that you start to ask yourself “What can I measure next?” at regular intervals… ;-)

  2. Wil je ruilen met mijn Tek 2232?

    • Ha… nee, maar ik verzeker je dat er over twee jaar weer veel mooiere zijn (enne… mooi ding, die 2232 specs zijn best indrukwekkend!).

  3. Based on these articles I’ve just ordered one of these for my company. I hope it’s as good as it looks! :o) Am I right in thinking you can connect it to a large PC monitor via a DVI cable too? Also all the graphs you are posting, are these all done using the PC software or are you capturing images on the scope to USB key?

    • Haven’t tried the DVI yet, but yeah it’s present. I use the USB key to transfer screen shots, since I rarely use Windows.

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