Spinning CRT Makes A 360 Degree Audio Oscilloscope

September 16, 2023 by Dan Maloney 9 Comments

A question for you: if the cathode ray tube had never been invented, what would an oscilloscope look like? We’re not sure ourselves, but it seems like something similar to this mechanical tachyscope display might worked, at least up to a point.

What’s ironic about this scenario is that the tachyscope [Daniel Ross] built actually uses a CRT from a defunct camcorder viewfinder as the light-up bit of what amounts to a large POV display. The CRT’s horizontal coil is disconnected while the vertical coil is attached to the output of a TEA205B audio amplifier. The CRT, its drive electronics, and the amp are mounted to a motorized plastic platter along with a wireless baby monitor, to send audio to the CRT without the need for slip rings — although a Bluetooth module appears to be used for that job in the video below.

Speaking of slip rings, you’d expect one to make an appearance here to transfer power to the platter. [Daniel] used a slip ring for his previous steampunk tachyscope, but this time out he chose a hand-wound air core transformer, with a stationary primary coil and secondary coil mounted on the platter. With a MOSFET exciter on the primary and a bridge rectifier on the secondary, he’s able to get the 12 volts needed to power everything on the platform.

Like most POV displays, this one probably looks better in person than it does in video. But it’s still pretty cool, with the audio waveforms sort of floating in midair as the CRT whizzes around. [Daniel] obviously put a lot of work into this, not least with the balancing necessary to get this running smoothly, so hats off for the effort.

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STM32 Oscilloscope Uses All The Features

August 8, 2023 by Bryan Cockfield 29 Comments

[jgpeiro] is no slouch when it comes to building small, affordable oscilloscopes out of common microcontrollers. His most recent, based on an RP2040 with two channels that ran at 100 MSps, put it on the order of plenty of commercially-available oscilloscopes at this sample rate but at a fraction of the price. He wanted to improve on the design though, making a smaller unit with a greatly reduced bill-of-materials and with a more streamlined design, so he came up with this STM32-based oscilloscope.

The goal of this project was to base as many of the functions around the built-in capabilities of the STM32 as possible, so in addition to the four input channels and two output channels running at 1 MHz, the microcontroller also drives a TFT display which has been limited to 20 frames per second to save processor power for other tasks. The microcontroller also has a number of built-in operational amplifiers which are used as programmable gain amplifiers, further reducing the amount of support circuitry needed on the PCB while at the same time greatly improving the scope’s capabilities.

In fact, the only parts of consequence outside of the STM32, the power supply, and the screen are the inclusion of two operational amplifiers included to protect the input channels from overvoltage events. It’s an impressive build in a small form factor, and we’d say the design goal of keeping the parts count low has been met as well. If you do need something a little faster though, his RP2040-based oscilloscope is definitely worth checking out.

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The Simplest Curve Tracer Ever

August 2, 2023 by Dan Maloney 15 Comments

To a lot of us, curve tracing seems to be one of those black magic things that only the true wizards understand. But as [DiodeGoneWild] explains, curve tracing really isn’t all that complicated, and it doesn’t even require specialized test instruments — just a transformer, a couple of resistors, and pretty much whatever oscilloscope you can lay your hands on.

True to his handle, [DiodeGoneWild] concentrates on the current-voltage curves of Zener diodes in the video below, mainly as a follow-up to his recent simple linear power supply project, where he took a careful look at thermal drift to select the best Zener for the job. His curve tracer is super simple — just the device under test in series with a bunch of 10-ohm resistors and the secondary winding of a 12-volt transformer. The probes of his oscilloscope — a no-frills analog model — go across the DUT and the resistor, and with the scope in X-Y mode, the familiar current-voltage curve appears. Sure, the trace is reversed, but it still provides a good visualization of what’s going on. The technique also works on digital scopes; just be ready for a lot of twiddling to get into X-Y mode and to get the trace aligned.

Of course it’s not just diodes that can be tested with a curve tracer, and [DiodeGoneWild] showed a bunch of other two-lead components on his setup. But for our money, the neatest trick here was using a shorted bridge rectifier to generate a bright spot on the curve to mark the zero crossing point. Clever indeed, and pretty useful on a scope with no graticule.

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Examining Test Gear From Behind The Iron Curtain

August 1, 2023 by Al Williams 8 Comments

Back in 1978, an oscilloscope was an exotic piece of gear for most homebrewers. We expect they were even more rare in private hands behind the iron curtain, and [Thomas Scherrer] shows us a Soviet X1-7B combination oscilloscope and spectrum analyzer (he thinks, at least, it is a spectrum analyzer) that he got working.

The Soviet scope is clearly different with its Cyrillic front panel. Luckily, Google Translate was up to the task of decoding a picture of the device. However, the differences aren’t just cosmetic. The scope also has a very interesting rotating bezel around the round CRT. You can see a video of the 8.2 kg scope below.

A quick look inside looks pretty conventional for a scope of that era that used all transistors in the circuitry. The rotating bezel, though, also controls something that looks like a big mechanical switch and cavity or, perhaps, a big mechanical variable component of some kind.

Satisfied that the insides were in reasonable shape, [Thomas] was ready to try turning it on. We want to say it went well, but… there was censored audio, along with a loud noise, right after it was plugged in. Troubleshooting centered on what was producing a burned smell, but a quick examination didn’t turn up anything obvious, despite being localized to the power circuitry. The fuse didn’t blow, oddly, and — even more puzzling — the unit was off when plugged in!

It turns out the input power filter leaked to the chassis. Since he had a ground on the chassis, that explained the failure, and while it was annoying, it was better than getting a shock with a hot chassis. The second plug in went better.

It finally did work, at least somewhat, although he never explored some of the odd features the scope appears to have. We love the old boat anchor scopes but don’t see many Soviet instruments, at least not those of us on this side of the Atlantic.

We do see a few Soviet-era computers now and again. As for the fuse not blowing, it was shorted before the fuse, but apparently, fuses don’t always blow when you expect them to, anyway.

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Grab Your ‘Scope’s Screen From The Command Line

July 25, 2023 by Jenny List 9 Comments

Many of us have oscilloscopes and other instruments with built-in digital interfaces, but how many of us use them? [Andrej Radović] has a Tektronix TDS2022 which can print its screen to any of its various interfaces, and he set about automating the process of acquisition with a Bash script.

The easiest interface to use was the trusty serial port — hardly the fastest but definitely the best supported. But how does one retrieve an image fired down a serial port? Most of the post is devoted to spotting file headers in a Bash script monitoring the serial port, and streaming the result to a local file. There’s a discussion of the various formats supported by the Tek, with an ancient PCX bitmap format being chosen over Postscript for speed. The result is a decent quality screen grab, making the ‘scope that little bit more useful and perhaps extending its life.

Perhaps your instrument isn’t a TEK, but the chances are you can still make it bend to your will from a PC. Try it, with the magic of VISA.

Remote Code Execution On An Oscilloscope

July 17, 2023 by Bryan Cockfield 10 Comments

There are a huge number of products available in the modern world that come with network connectivity now, when perhaps they might be better off with out it. Kitchen appliances like refrigerators are the classic example, but things like lightbulbs, toys, thermostats, and door locks can all be found with some sort of Internet connectivity. Perhaps for the worse, too, if the security of these devices isn’t taken seriously, as they can all be vectors for attacks. Even things like this Rigol oscilloscope and its companion web app can be targets.

The vulnerability for this oscilloscope starts with an analysis of the firmware, which includes the web control application. To prevent potentially bricking a real oscilloscope, this firmware was emulated using QEMU. The vulnerability exists in the part of the code which involves changing the password, where an attacker can bypass authentication by injecting commands into the password fields. In the end, the only thing that needs to be done to gain arbitrary code execution on the oscilloscope is to issue a curl command directed at the oscilloscope.

In the end, [Maunel] suggests not connecting this oscilloscope to the Internet at all. He has informed the producer about it but as of this writing there has not been a resolution. It does, however, demonstrate the vulnerabilities that can be present in network-connected devices where the developers of the software haven’t gone to the lengths required to properly secure them for use with the modern Internet. Even things not connected to a traditional Internet connection can be targets for attacks.

Own More Than One ‘Scope? You’ve Got Nothing On This Guy!

May 24, 2023 by Jenny List 18 Comments

We’re guessing that quite a few of our readers have a surprising amount of redundant test gear, and we ourselves have to admit that more than one instrument adorns our benches. But we are mere dilettantes, amateurs if you will, compared to [Volke Kloke]. He’s got 350 of them in his average American home, and we have to say, among them are some beauties.

The linked newspaper article is sometimes frustratingly light on the details, but fortunately he has a website all of his own where we can all get immersed in the details. Of particular interest is an instrument which doesn’t even have a CRT, the General Radio 338 string oscillograph used a mirror drum to catch a standing wave in a tungsten wire, but there are plenty more. Is your first ‘scope among them?

As we now live in the age of cheap digital ‘scopes, at any surplus sale you’ll see plenty of CRT-based instruments going for relative pennies. Of those, the more recent and high-end ones are still extremely useful instruments, and it’s not just misty-eyed reminiscing to say that they remain a worthy addition to any bench.

Want to know about early ‘scope tech? We’ve taken a look before.