Homebrew Analog Scope Project Log

[GK] had some old CRTs lying around, so naturally he decided to build an old school analog scope with one of them. Lucky for us, he’s been documenting his progress. Since it was a big project to tackle, he started out with Spice modeling to work out all the right values.

Prototyping the power supply took some custom transformer winding, but when done, the power supply did the job. Although he’s still wiring up the Z (intensity) axis, the scope is already capable of displaying signals and even text characters using a character generator he built earlier (see video below).

[GK] spends most of the time so far talking about the high voltage power supply design. For the particular tubes he had on hand he needed +200V, -400V, -550V, and 6.3VAC for the CRT heater. This is certainly not the typical Arduino-based digital scope that everyone builds at least once.

We love analog scopes for art projects, logic analyzer conversions, and gaming. Of course, if you don’t have an old CRT in your parts bin, you might consider trying a laser.

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Headphone Amp Features A Tiny CRT

[ErikaFluff] needed an amp for his Grado open cans. Rather than build yet another boring black box, he built what may be the most awesome headphone amp ever. [ErikaFluff] added a tiny CRT to the project, which displays the current audio waveform passing through the amp. He packaged all this up in a customized Hammond box which makes it look like it just rolled off the line from some audiophile studio.

The amplifier in this case is based upon the CMoy, a common headphone amp design. [ErikaFluff] added a MOSFET on the output to drive his relatively low impedance (32 ohm) Grado headphones with reasonable volume. The CRT is from an old video camera viewfinder. Before LCDs were advanced and cheap enough to include in video cameras, CRTs were the only show in town. These tiny black and white screens use high voltage to scan an electron beam across a phosphor screen just like their bigger brethren.

In action! - ImgurSince he was going with an oscilloscope style vector scan rather than the raster scan the screen electronics were originally designed for, [ErikaFluff] had to create his own horizontal and vertical deflection circuits. Horizontal scan is created by a 555 timer generating a sawtooth wave at 75 Hz. Vertical deflection is via an LM386 driving a hand wound impedance matching transformer. The high voltage flyback transformer and its associated driver circuit were kept from the original CRT, though repackaged to make them as small as possible.

You might think that having a few thousand volts next to a sensitive audio amplifier would cause some noise issues. We also worried a bit about shorts causing unexpected shock treatments through the wearer’s ears. [ErikaFluff] says there is no need to for concern. The signal is fed to the CRT circuit through optocouplers. The audio circuit is also electrically split from the CRT and runs on a virtual ground. Judicious amounts of shielding tape keeps the two circuits isolated.

This may not be the most practical project, but we think it’s pretty darn cool. The response over on Reddit’s electronics subreddit seems to be positive as well. We hope [ErikaFluff] is sitting down when this post gets published!

A Revolutionary Input Device, 30 Years Too Late

Way before you kids had touch screens and mice, we had to walk uphill both ways to tell a computer where we were pointing at on the screen. I speak, of course, of light pens. When these photodiodes in a pen were pointed at a CRT, the display driver would tell the computer where the pen was pointing. It’s a pretty incredible video hack today, and these things were around in the 1970s. You could, of course, use a light pen with most of the old 8-bit home computers, including the Commodore 64.

[Jan] has a soft spot for the light pen on the C64. So much so he made a new input device using this tech. It’s great, and if this existed in 1985, all the cool kids would have known about it.

The build is called the LightHammer. It’s a light pen, inside the head of a plastic hammer, with a few springs, nuts, and washers to tell the computer to read the light pen input. The light pen itself is just a photodiode with a few transistors; it was a simple circuit in the 80s, and it’s a simple circuit today.

A new input device isn’t worth anything without an app to show off the tech, and [Jan] is about three steps ahead of us here. He wrote a game for this LightHammer – a digital version of Whac-A-Mole and Simon. They’re exactly what you think they are: the classic ‘repeat the computer’ and ‘murder rodents’ games.

If that’s not enough, [Jan] also built an arcade cabinet for his C64 setup, with the monitor, joysticks, a 1541, and a TV mounted in a cabinet that would look great in a bar. You can check out a video of that and the games using the LightHammer below.

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Battlezone Played on Vector Display with Hand-Wound Yoke

We’ve been admirers of the work [Eric] and friends have been doing over at TubeTime for years. One of the earliest we can remember is the decatron kitchen timer, and we still tell the story of [Eric] purposely leaving out button debouncing in order to make his vector flappy bird even harder.

TubeTime is back at it this year and we had the opportunity to speak with them at Bay Area Maker Faire. The group specializes in working with old tube displays and this year’s offering was spectacular in many ways. First off, the software side of things is an emulator running on an STM32 F4 Discovery board. The chips on these boards have a pair of 12-bit DACs which are driving the X and Y of the vector displays. Code to run the original ROMs was ported from existing projects, but the audio for the games was kind of a hack to get working.

This particular display is where things get really fascinating. The tube itself was originally manufactured as test equipment for television repairmen. What’s fascinating about this is that [Eric] had to rewind the deflection yokes himself to get it working again. Luckily he documented quite a bit about his initial research into this process and his experiments to remedy some distortion issues he encountered once it was working.

Make sure to head on over to TubeTime and read their overview of the Battlezone machine. After the break we’ve also embedded a few of our own pictures as well as the interview at BAMF.

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Caption CERN Contest – Tabletop Projection

Week 17 of the Caption Cern Contest on Hackaday.io is now a polished sheet metal memory, but the captions live on! Thanks to everyone who entered. We may never know exactly what these scientists and their ladder holding friend were up to. We do know a bit more about some of the equipment in that photo though! Astute reader [Pierlu] dropped a photo comment here on the Blog showing some interesting lawn ornaments over at CERN. The device to the right looks quite a bit like the device on the right side of our original image. We don’t have a close-up to be sure, but chances are this is part of a Cockcroft–Walton generator.

The Funnies:

  • “…and six cute little kittens, too. I wonder how she got in here? Hey, hold that ladder steady, Schrödinger!” – [sbi.gaijin]
  • “Good news: the shrink ray worked. Bad news: we have to escape the janitor’s vacuum cleaner” – [Cody]
  • “Archeology Professor Ammit Duat from the University of Cairo, assisting CERN engineer Jack Orsiris in changing the locks on the door to the Egyptian underworld” – [carbonfiber]

This week’s winner is [alj5432] with “Sticking with CERN’s usual “Go Big or Go Home” theme,
scientists make adjustments to LHC’s massive “Press To Start” Button.” We’re sure [alj5432] will enjoy probing digital circuits with his new Logic Pirate From The Hackaday Store! Congratulations [alj5432]!

Week 18

CEcern-18-smRN is no stranger to innovative display systems. That should be no surprise, considering CERN staff are trying to work with massive amounts of data collected by thousands of scientists. Here we see one of those systems, a projection table of some sort.

Today video projectors are relatively cheap and easy to make, thanks to advances in LCD and MEMS technology. Back when this image was shot in 1979 though, video projectors were expensive and rare commodities. What was this scientist doing?

You tell us!

Once again, we’re giving away a Logic Pirate from The Hackaday Store.

Add your humorous caption as a comment to this project log. Make sure you’re commenting on the contest log, not on the contest itself.

As always, if you actually have information about the image or the people in it, let CERN know on the original image discussion page.

Good Luck!

1.37″ CRT Restored by Hacklab for Miniature MAME Cabinet

For $5, [William] of Toronto’s Hacklab hackerspace got a hold of one of the smallest CRT screens ever made – about the size of a large coin. Over the course of a couple sessions – including a public hack boothside at their Mini Makerfaire – [William], [Igor], and several other members managed to connect it as a monitor directly off a Raspberry Pi. The end-goal is the world’s smallest MAME cabinet (smaller by almost half than this LCD one).

As Canada followed the US and stopped broadcasting analog back in 2011, it became quite a challenge to feed the screen a video source. They disclosed early that the easiest solution would just be an RF transmitter on the Pi and then tune the micro-set to that channel. Too easy. They wanted something elegant and challenging so they went digging into the circuitry to find a place to insert a composite video signal directly.

The real story here is their persistence at reverse engineering. The PCB was folded like a cardboard box to fit in the original case, making large portions of the circuitboard and wiring inaccessible. Even when they managed to trace the signal to what they thought was the appropriate chip (marked C80580), they could not find any information on the 30 year old chip. Noting that every other chip on the board was Panasonic and started with “AN5”, [Igor] suspected the mystery silicon was just renamed and went through every single datasheet he could find with that prefix. Combined with form factor, pin count and purpose, his sleuthing was rewarded with a guess for a match – the AN5715. His hunch was correct – using that datasheet led him to the answers they required.

Then they just had to figure out how get the composite signal the Pi outputted into something the chip would use to display the correct image. There were no shortage of challenges, failures and dead ends here either, but they had help from the rest of their membership.

Their project log is an interesting narrative through the process and in the end of course, it worked. It is displayed beautifully with a clear acrylic case and ready for a cabinet to be built.

RGB Video Input Hack is a Master Hack for CRT Televisions

What’s shown on the screen above is about half-way through the process of hacking RGB video into a CRT television that’s not supposed to have it. The lettering is acting a bit like a layer mask, showing bits of the Super Mario Bros. start screen which is being injected from an original Famicom. [Michael J. Moffitt] figured out that he could patch his signals into the multiplexer which is responsible for overlaying the TV’s menu system. Obviously you can’t get your Mario on with this view, but the next step was as simple as finding the blanking pin and tying it 5V. Brilliant.

This particular hack is worthy of recognition. But read through [Michael’s] write up and it’s obvious that he knows the driver circuitry beyond the realm of normal curiosity. If you ever get stuck while trying to do something custom, we’d recommend pinging him with your questions (sorry [Michael] but with great knowledge comes great responsibility).