Hackaday Podcast Ep8 – The Art Episode: Joe Kim, Strings And CRTs, Hydrogen Done 2-Ways

We know you love the original art on Hackaday. Those fantastic illustrations are the work of Joe Kim, and he joins us as a guest on this week’s episode to talk about his background, what inspires him, and how he pulls it all off.

This episode is still packed with hacks. Editors Mike Szczys and Elliot Williams somehow stumble into two projects that end up generating hydrogen (despite that not being their purpose). But that art angle this week goes beyond Joe’s guest appearance as we look at a hack to add green curve tracing goodness on a black and white CRT, and an incredible take on a string art building machine. We get a look at interesting hardware that landed on the clearance rack, ultralight robots that move with flex PCB actuators, a throwback to mechanical computing, and giving up control of your home heating and cooling to a Raspberry Pi.

Links for all discussed on the show are found below. As always, join in the comments below as we’ll be watching those as we work on next week’s episode!

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Curve Tracing On Spray Painted CRTs

A Lissajous curve is formed when two sine waves plotted on their respective X and Y axes. You can see one using an oscilloscope and a couple of signal generators, if you play with one of those ‘pendulums tracing in the sand’ toys, or if you really need something sciencey for your home decor you can trace them out with a disassembled CRT. That’s what [Emily] did with the LissaJukebox. It traces curves. No, it’s not a curve tracer, that’s another tool altogether

If you’re going to put squigglies on a CRT, you obviously need a CRT, and it needs to look good. There are a few options out there, from old oscilloscope tubes, the CRTs found in old VHS camcorders, to tiny electrostatic tubes that are slightly easier to drive. For this build, [Emily] chose an old, bog-standard, black and white television. But the screen is green, right? Yeah, but if you carefully mask off a CRT and buy some stained glass spray paint, a CRT can be any color you want. Except for purple, the purple stained glass spray paint didn’t work for some reason.

To generate the various functions, [Emily] used an XR2206 function generator, sold in kit form on Amazon, eBay, and various other online retailers for a pittance. One of these function generators controls the X axis, another the Y, and both of these generators are fed into a 15 Watt stereo amplifier board to run the deflection coils in the CRT. If you’re following along at home, yes, this is dangerous. Don’t touch the CRT or it will stop your heart. Those of us whose hearts are as black as coal are safe.

There were a few modifications needed to turn the XR2206 function generator ‘kit’ into something a bit more useful for this project. The through-hole pots were replaced with panel-mount pots, and the range/amplitude setting is now controlled with a rotary switch.

Is it useful? Well, actually, if you’re building a set for a TV show and you need something that looks ‘sciencey’, a LissaJukebox should be right up your alley. Other than that it looks pretty, and we now know there’s a spray paint that will turn your old, boring black and white CRT into a glorious amber phosphor. Can’t beat that.

Op Amps Combine Into Virtual Ball In A Box

What happens when you throw a ball into a box? In the real world, the answer is simple – the ball bounces between the walls and the floor until it eventually loses energy and comes to rest. What happens when you throw a virtual ball into a virtual box? Sounds like something you might need a program running on a digital computer to answer. But an analog computer built with a handful of op amps can model a ball in a box pretty handily too.

OK, it takes quite a large handful of op amps and considerable cleverness to model everything in this simple system, as [Glen Kleinschmidt] discovered when he undertook to recreate a four-decade-old demonstration project from AEG-Telefunken. Plotting the position of an object bouncing around inside the virtual box is the job of two separate circuits, one to determine the Y-coordinate and bouncing off the floor, and one to calculate the X-coordinate relative to the walls. Those circuits are superimposed by a high-frequency sine-cosine pair generator that creates the ball, and everything is mixed together into separate outputs for an X-Y oscilloscope to display. The resulting simulation is pretty convincing, with the added bonus of the slowly decaying clicks of the relay used to change the X direction each time a wall is hit.

There’s not much practical use, but it’s instructional for sure, and an impressive display of what’s possible with op amps. For more on using op amps as analog computers, check out [Bil Herd]’s “Computing with Analog” article.

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Salvaged Scope Lets You Watch The Music

Everyone likes a good light show, but probably the children of the 60s and 70s appreciate them a bit more. That’s the era when some stereos came with built-in audio oscilloscopes, the search for which led [Tech Moan] to restore an audio monitor oscilloscope and use it to display oscilloscope music.

If the topic of oscilloscope music seems familiar, it may be because we covered [Jerobeam Fenderson]’s scope-driving compositions a while back. The technique will work on any oscilloscope that can handle X- and Y-axis inputs, but analog scopes make for the best display. The Tektronix 760A that [Tech Moan] scrounged off eBay is even better in that it was purpose-built to live in an audio engineer’s console for visualizing stereo audio signals. The vintage of the discontinued instrument isn’t clear, but from the DIPs and discrete components inside, we’ll hazard a guess of early to mid-1980s.  The eBay score was a bargain, but only because it was in less that perfect condition, and [Tech Moan] wisely purchased another burned out Tek scope with the same chassis to use for spares.

The restored 760A does a great job playing [Jerobeam]’s simultaneously haunting and annoying compositions; it’s hard to watch animated images playing across the scope’s screen and not marvel at the work put into composing the right signals to make it all happen. Hats off to [Tech Moan] for bringing the instrument back to life, and to [Jerobeam] for music fit for a scope.

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GNU Radio Drives Oscilloscope

These days we are spoiled with a lot of cheap test equipment. However, you can do a lot of measurements with nothing more than an oscilloscope. Add something like a signal generator and you can do even more. One classic technique for frequency measurement, for example, is using a scope to display a Lissajous pattern. [Franz Schaefer] has a video showing how to generate these useful curves with GNU Radio.

As we pointed out earlier, GNU Radio doesn’t have to be about radio–it is really just a Python-based signal processing laboratory. [Franz] uses GNU Radio Companion to create blocks which in turn create the patterns on an old analog scope.

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Transformer Inductive Coupling Simulation Is SFW

[James] has a friend who teaches at the local community college. When this friend asked him to build a transformer coupling simulation, he was more than happy to oblige. Fortunately for us, he also made a video that explains what is happening while  showing the output on a ‘scope.

For the simulation, [James] built primary and secondary coils using PVC pipe. The primary coil consists of 11 turns of 14AWG stranded wire with 4V running through it applied. The first secondary he demonstrates is similarly built, but has 13 turns. As you’ll see, the first coil induces ~1.5V in the second coil. [James] first couples it with the two windings going the same way, which results in the two 2Mhz waveforms being in phase with each other. When he inserts the secondary the other way, its waveform is out of phase with the primary’s.

His second secondary has the same diameter PVC core, but was wound with ~60 turns of much thinner wire—28AWG bell wire to be exact. This match-up induces 10V on the secondary coil from the 4V he put on the primary. [James]’ demonstration includes a brief Lissajous pattern near the end. If you don’t know enough about those, here’s a good demonstration of the basics coupled with an explanation of the mechanics behind them.

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Three Pendulum Harmonograph

Just the other day we were thinking “You know what we need more of around here? Harmonographs!” And our requests were answered when [Paul] sent in his three pendulum harmonograph. For those unaware, it’s a mechanical device that draws Lissajous curves or “really cool circles” to quote some of our staff.

[Paul] includes all the plans necessary to make your own harmonograph and begin drawing today. If you can’t wait, there’s a video of the three pendulum harmonograph etching a masterpiece after the jump. Continue reading “Three Pendulum Harmonograph”