Long PCB Shows Effects of Ludicrous Speed

Transmission lines can seem like magic. When you make use of them it seems strange that a piece of wire can block or pass certain frequencies. It is less common to use transmission lines with pulses and typically your circuit’s transmission line behavior isn’t all that significant. That is, until you have to move a signal a relatively long distance. [Robert Baruch] has been using a long PCB to test pulse behavior on a bus he’s working on. He actually has a few videos in this series that are worth watching.

What makes it interesting is that [Robert] has enough distance on the board to where light-speed effects show up. By using a very nice DPO7104 oscilloscope and a signal generator, he shows how the signal reflects on the line at various points, adding and subtracting from it. The measurements matched theory fairly closely. You shouldn’t expect them to match exactly because of small effects that occur randomly throughout the system.

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A DIY Nine Channel Digital Scope

Have you ever found yourself in the need of a nine channel scope, when all you had was an FPGA evaluation board? Do not despair, [Miguel Angel] has you covered. While trying to make sense of the inner workings of a RAM controller core, he realized that he needed to capture a lot of signals in parallel and whipped up this 9-channel digital oscilloscope.

The scope is remote-controlled via a JavaScript application, and over Ethernet. Graphical output is provided as a VGA signal at full HD, so it is easy to see what is going on. Downloading sampled data to the controlling computer for analysis is in the works. [Miguel] runs his implementation on an Arty A7 development board which is currently available for around a hundred dollars, but the design is transferable to other platforms. The code and some documentation is available on GitHub and there is a demo video after the break.

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Ocelot Arcade System Illustrates the Scope of Vector Graphics

Who knows how far the Vectrex system, or vector graphics gaming in general could have gone if not for the crash of ’83? The console wars might have been completely different if not for this market saturation-based reset button.

[Matt Carr] doesn’t own a Vectrex, but he does have a Tektronix 465 oscilloscope. After an intense labor of love and documentation, he also has a shiny new vector graphics arcade system that he built himself. It’s based on a dsPIC33 and uses a dual-channel DAC to produce wire frame 3-D graphics and send X-Y coordinates to the ‘scope via phono outputs. The PIC’s internal DAC is meant for audio and didn’t do so well with graphics, so [Matt] used a TLV5618A piggybacked on the PIC’s DAC pins.

The Ocelot doesn’t take cartridges, though it might someday. For now, changing games means getting out the PICkit. There are currently two to choose from: Star Lynx, an awesome flying shooter where you get to save a feline population, and Mattsteroids, which is exactly what it sounds like. There’s only one Ocelot in existence, and although it isn’t for sale, [Matt] has terrific technical documentation should you care to replicate it. One thing you might not be able to replicate is the awesome vintage advert he made for the Ocelot, which is cued up after the break.

Don’t have a ‘scope? You can do vector graphics on a CRT with an FPGA.

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Watch Video on a Oscilloscope with an ESP32

[bitluni] got a brand new scope, and he couldn’t be happier. No, really — check the video below; he’s really happy. And to celebrate, he turned his scope into a vector display using an ESP32.

Using a scope in X-Y mode is nothing new, of course. The technique is used to display everything from Lissajous patterns from an SDR to bouncing balls from an analog computer. Taken on as more of an exercise to learn how to use his new tool than a practical project, [bitluni]’s project starts by using two DACs on an ESP32 to create simple Lissajous patterns to learn about the scope’s controls. Next he built some code to display 3D point clouds, but learned that the native DAC code wasn’t up to the job. A little hacking improved the speed 27-fold, which was enough for great 3D images and live video from an I²S camera module. The latter was accomplished by grabbing frames from the camera and rendering them pixel by pixel, CRT style. The results are pretty clean, and there’s a lot to be learned about both using scopes as X-Y displays and tweaking the ESP32 for maximum performance.

Need more background on the ESP32? Start by checking out these ESP32 tutorials.

 

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Fully-functional Oscilloscope on a PIC

When troubleshooting circuits it’s handy to have an oscilloscope around, but often we aren’t in a lab setting with all of our fancy, expensive tools at our disposal. Luckily the price of some basic oscilloscopes has dropped considerably in the past several years, but if you want to roll out your own solution to the “portable oscilloscope” problem the electrical engineering students at Cornell produced an oscilloscope that only needs a few knobs, a PIC, and a small TV.

[Junpeng] and [Kevin] are taking their design class, and built this prototype to be inexpensive and portable while still maintaining a high sample rate and preserving all of the core functions of a traditional oscilloscope. The scope can function anywhere under 100 kHz, and outputs NTSC at 30 frames per second. The user can control the ground level, the voltage and time scales, and a trigger. The oscilloscope has one channel, but this could be expanded easily enough if it isn’t sufficient for a real field application.

All in all, this is a great demonstration of what you can accomplish with a microcontroller and (almost) an engineering degree. To that end, the students go into an incredible amount of detail about how the oscilloscope works since this is a design class. About twice a year we see a lot of these projects popping up, and it’s always interesting to see the new challenges facing students in these classes.

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Current Measurement with Oscilloscopes

What do a Rogowski coil, a magnetic core, and a hall effect sensor have in common? They are all ways you can make oscilloscope probes that measure current. If you think of a scope as a voltage measurement device, you ought to watch the recent video from Keysight Technology (see below). It is true that Keysight would love to sell you a probe, but the video is not a sales pitch, just general technical information about making current measurements with an oscilloscope.

Of course, you can always measure the voltage across a shunt resistor — either one that is naturally in the circuit or one you’ve put inline just for measuring purposes. But if you add a resistor it will change the circuit subtly and it may have to handle a lot of power.

The Keysight video points out that there are different probes for different current measurement regimes. High current, medium current, and low current all use different probes with different technologies. The video is only about 6 minutes long and if you’ve never thought about measuring current with a scope, it is worth watching.

The video shares some high-level details of how the current probes work — that’s where the Rogowski coil comes in, for example. Of course, you can’t expect a vendor to tell you how to build your own current probes. That’s OK, though, because we will. Current probes are often expensive, but you can sometimes pick up a deal on a used one.

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DS212 Oscilloscope Review: Open Source and Great for Hacking

We’ve seen plenty of oscilloscopes that look like repurposed cell phones. Usually, though, they only have one channel. The DS212, has two channels and a signal generator! [Marco] gives his review and a quick tear down in the video below.

The scope isn’t going to replace a big bench instrument, but for a portable scope with a rechargeable battery, it isn’t bad. The 1 MHz analog bandwidth combines with a 10 megasample per second front end and 8K of sample memory. The signal generator can produce basic waveforms up to 1 MHz. We were somewhat surprised the unit didn’t sport a touch screen, which is why you can see [Marco’s] fingers in the screenshot above. He seems to like the dual rotary encoder system the devices uses for navigation.

Where this really stands out is that it is open source for the the firmware running on the STM32 processor inside. We so rarely see this for commercially available bench tools and it makes this a fine hacking platform. It’s easy to imagine adding features like digital signals out and decoding digital data. It would be interesting to marry it with a WiFi chip and use it as a front end for another device over WiFi. Lots of possibilities. [Marco] shows that even though he’s not familiar with the STM32, he was able to add a custom waveform output to the device easily. This has the potential to be a custom troubleshooting platform for your builds. Lining up all of the sensing and signal generation settings for each specific type of test means you don’t need a guru to walk through the common failure modes of a product.

There are many small inexpensive scopes out there that might not match a big bench instrument but can still be plenty useful. [Jenny List] just reviewed one that comes in at around $21. And last year, we saw a sub-$100 scope that would net you just one channel scope. That’s progress!