Choosing A ‘Scope: Examining Bandwidth

A few weeks ago I asked the Hackaday community for some help and advice in buying a new budget oscilloscope. Thank you very much to those of you who responded both here online and in person among my friends closer to home. I followed the overwhelming trend in the advice I received, and bought myself a Rigol DS1054z, an instrument with which I am very happy. It’s a nominally a 50 MHz scope, but there’s a software hack that can bring it up to 100 MHz. How fast can it go?

My trusty Cossor, its 2 MHz bandwidth as yet unverified.
My trusty Cossor, its 2 MHz bandwidth as yet unverified.

This question became a mini scope-shootout after a conversation with my Hackaday colleague [Elliot] about measuring oscilloscope bandwidth, and then my fellow Oxford Hackspace members producing more than one scope for comparison. You know who you are, thank you. I found myself with ready access to several roughly equivalent models and one very high-end one in specification terms representing different strata of test equipment manufacture, and with the means to examine their performance.

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Ask Hackaday: Help Me Choose A ‘Scope

If there is one instrument that makes an electronic engineer’s bench, it is the oscilloscope. The ability to track voltages in the time domain and measure their period and amplitude is one akin to a light in the darkness, it turns a mere tinkerer with circuits into one in command of them. Straightforward add-on circuits can transform a basic oscilloscope into a curve tracer, frequency response display, and much more, and modern oscilloscopes offer a dizzying array of useful measurement features unimaginable to engineers only a few years ago. And I need your help to pick a new one.

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Flashed the wrong firmware? Swap out the LCD to match!

We always joke about the hardware guys saying that they’ll fix it in firmware, and vice-versa, but this is ridiculous. When [Igor] tried to update his oscilloscope and flashed the wrong firmware version in by mistake, he didn’t fix it in firmware. Instead, he upgraded the LCD display to match the firmware.

See, Siglent doesn’t make [Igor]’s DSO any more; they stopped using the 4:3 aspect ratio screens and replaced them with wider versions. Of course, this is an improvement for anyone buying a new scope, but not if you’ve got the small screen in yours and can’t see anything anymore. After playing around with flashing other company’s firmware (for a similar scope) and failing to get it done over the JTAG, he gave up on the firmware and started looking for a hardware solution.

It turns out that a few SMT resistors set the output screen resolution. After desoldering the appropriate resistors, [Igor] bought a new 7″ LCD screen online only to find out that it has a high-voltage backlight and that he’d need to build an inverter (and hide the noisy circuit inside his oscilloscope). Not daunted, he went digging through his junk box until he found a backlight panel of the right size from another display.

Yet more small soldering, and he had frankensteined a new backlight into place. Of course, the larger LCD won’t fit the case without some cutting, double-sided tape, and a healthy dose of black tape all around insulates the loose electricals. Et voilá!

We have to hand it to [Igor], he’s got moxie. It’s an ugly hack, but it’s a definite screen upgrade, and a lesser hacker would have stopped after flashing the wrong firmware and thrown the thing in the trash. We’d be proud to have that scope sitting on our desk; it’s a definite conversation starter, and a badge of courage to boot.

Connecting an old scope to a computer

Scope

A friend of [Michael]’s said his company was getting rid of some old lab equipment and asked him if he wanted a very large and very old digital storage oscilloscope. A ‘hell yes’ and we’re sure a few beers later, [Michael] found an old Gould 200 MHz four-channel scope on his bench. Even 20 years after its production it’s still a capable tool, but the serial ports on the back got [Michael] wondering – would it be possible to plot the screen of the scope on his computer?

The scope has three ports on the back – GPIB, miscellaneous I/O, and RS423. The latter of those ports is similar enough to RS232 that a USB to Serial converter just might work, and with the help of a null modem cable and a terminal, [Michael] was able to connect to this ancient scope.

In the manual, [Michael] found a the serial commands for this scope. The most useful of these is a command that prints out the contents of the scope’s trace memory as a series of 1-byte integers. With a short bit of PERL programming, [Michael] can create a PDF plot of whatever is on the scope’s screen. It’s formatted perfectly for Gnuplot, MATLAB, or even Excel.

Awesome work, and especially useful given these old scopes are slowly making their way to a technological boneyard somewhere.