classic hacks

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A Close Look At How Flip-Dot Displays Really Work

March 3, 2023 by 19 Comments

[Mike Harrison] has an upcoming project which will combine a large number of flip-dot displays salvaged from buses. [Mike] thought he knew how these things worked, and had a prototype PCB made right away. But while the PCB was being manufactured, he started digging deeper into the flip-dot’s flipping mechanism.

As he dismantled one of the flip-dots, he realized there was a lot going on under the hood than he realized. The dots are bistable — staying put when power is removed. This is achieved with a U-shaped electromagnet. The polarity of a driving pulse applied to the coil determines which way to flip the dot and saturates the electromagnet’s core in the process. Thus saturated, each dot is held in the desired position because the black side of the dot is made from magnetic material. But wait, there’s more — on further inspection, [Mike] discovered another permanent magnet mounted in the base. He’s not certain, but thinks its job is to speed up the flipping action.

Besides curiosity, the reason [Mike] is studying these so closely is that he wants to build a different driver circuit to have better and faster control. He sets out to better understand the pulse waveform requirements by instrumenting a flip-dot and varying the pulse width and voltage. He determines you can get away with about 500 us pulses at 24 V, or 1 ms at 12 V, much better that the 10 ms he originally assumed. These waveforms result in about 60 to 70 ms flip times. We especially enjoyed the slow-motion video comparing the flip at different voltages at 16:55 in the video after the break.

[Mike] still has to come up with the optimum driving circuit. He has tentatively has settled on a WD6208 driver chip from LCSC for $0.04/ea. Next he will determine the optimum technique to scale this up, deciding whether going for individual pixel control or a multiple sub-array blocks. There are mechanical issues, as well. He’s going to have to saw off the top and bottom margin of each panel. Reluctant to unsolder the 8500+ joints on each panel, his current idea is to solder new controller boards directly onto the back of the existing panels.

This video is a must-watch if you’re working on drivers for your flip-dot display project, and we eagerly look forward to any future updates from [Mike]. We also wrote about a project that repurposed similar panels a couple of years ago. There are a few details that [Mike] hasn’t figured out, so if you know more about how these flip-dots work, let us know in the comments below.

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A Thoroughly Modern Serial Terminal

March 1, 2023 by 16 Comments

The humble desktop serial terminal may have long disappeared from the world of corporate IT, but there are still plenty of moments when professionals and enthusiasts alike need to hook up to a serial port. Many of us use a serial port on our laptops or other mobile devices, but [Neil Crawforth] has gone one better than that with the VT2040. It’s an old-style serial terminal in a super-handy portable format, and as one might guess from the name, it has an RP2040 microcontroller at its heart.

Attached to the chip is a rather nice keyboard, and an ILI9488 480×320 LCD display. The software is modular, providing a handy set of re-usable libraries for the different functions including a PIO-based serial port. His main application seems to be talking to an ESP8266, but we’re guessing with a MAX232 or other level shifter chip it could drive a more traditional port. Everything can be found in the project’s GitHub repository, allowing anyone to join the fun.

As long-time readers will know, we’ve been partial to a few serial terminals in the past. Particularly beloved is this extremely retro model with vintage dot matrix LEDs.

Morse Code Clock For Training Hams

March 1, 2023 by 13 Comments

It might seem antiquated, but Morse code still has a number of advantages compared to other modes of communication, especially over radio waves. It’s low bandwidth compared to voice or even text, and can be discerned against background noise even at extremely low signal strengths. Not every regulatory agency requires amateur operators to learn Morse any more, but for those that do it can be a challenge, so [Cristiano Monteiro] built this clock to help get some practice.

The project is based around his favorite microcontroller, the PIC16F1827, and uses a DS1307 to keep track of time. A single RGB LED at the top of the project enclosure flashes the codes for hours in blue and minutes in red at the beginning of every minute, and in between flashes green for each second.

Another design goal of this build was to have it operate with as little power as possible, so with a TP4056 control board, single lithium 18650 battery, and some code optimization, [Cristiano] believes he can get around 60 days of operation between charges.

For a project to help an aspiring radio operator learn Morse, a simple build like this can go a long way. For anyone else looking to build something similar we’d note that the DS1307 has a tendency to drift fairly quickly, and something like a DS3231 or even this similar Morse code clock which uses NTP would go a long way to keeping more accurate time.

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Collection Of Old Films Rescued For Preservation

February 28, 2023 by 31 Comments

Periscope Film owners [Doug] and [Nick] just released a mini-documentary about the rescue of a large collection of old 35 and 16 mm celluloid films from the landfill. The video shows the process of the films being collected from the donor and then being sorted and organized in a temporary storage warehouse. There is a dizzying variety of films in this haul, from different countries, in both color and black and white.

We can see in the video that their rented 8 meter (26 foot) cargo truck wasn’t enough to contain the trove, so they dragged along a 1.8 x 3.6 m (6 x 12 ft) double-axle trailer as well. That makes a grand total of 49 cubic meters of space. Our back-of-the-envelope calculations says that filled to the brim, that would be over 30,000 canisters of 600 m (2,000 ft) 35 mm movie reels.

When it comes to preserving these old films, one big problem is physical deterioration of the film stock itself. You will know something is wrong when you get a strong acetic or vinegary odor when opening the can. [Nick] shows some examples where the film has even become solidified, taken on a hexagonal shape. It will take months to just assess and catalog the contents of this collection, with damaged films that are still salvageable jumping to the head of the queue to be digitized.

Film Scanning Artist [Esteban] Performing Color Correction
Films are digitized at 4K resolution using a Lasergraphics ScanStation archival quality film scanning system, and then the restoration fun begins. One issue demonstrated in this video is color deterioration. In the Eastmancolor film technology introduced in the 1950s, the blue dyes deteriorate over time. This, and a plethora of other issues, are corrected in the restoration process.

We’re particularly jealous of film scanning artist [Esteban]’s triple-headed trackball. We learned from a quick Google search this beast is merely the entry level control panel from UK company Tangent — they make even larger flavors.

If you’re interested in doing this with 8 mm home movies, we covered a project way back in 2011 of a DIY home movie scanning project. We also covered one of Periscope Film’s restored training films about NASA soldering techniques from 1958. Kudos to organizations who focus on keeping these types of interesting and historical films from being dumped in the landfill and lost forever.

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Digital Replica Of Antique Weather Monitoring Instrument

February 22, 2023 by 8 Comments

Computers and digital sensors have allowed for the collection and aggregation of data barely possible to imagine to anyone in the instrumentation scene even sixty years ago. Before that, things like weather stations, seismometers, level sensors, and basically any other way of gathering real data about the world would have been performed with an analog device recording the information on some sort of spool of paper. This was much more tedious but the one thing going for these types of devices was their aesthetic. [mircemk] is back to bring some of that design inspiration to a digital barometric display.

The barometer is based around an Arduino Arduino Nano and a relatively large I2C display to display the captured data. It also uses a BME 280 pressure sensor board, but the technical details of this project are not the focal point here. Instead, [mircemk] has put his effort in recreating the old analog barographs, which display barometric data on a spool of paper over time, on the I2C display. As the device measures atmospheric pressure, it adds a bar to the graph, displaying the data over time much as the old analog device would have.

We’ve discussed plenty of times around here that old analog meters and instrumentation like this recreation of a VU meter are an excellent way of getting a more antique aesthetic than is typically offered by digital replacements. Adding in a little bit of style to a project like this can go a long way, or you can simply restore the original antique instead.

Drawing Knots On An Oscilloscope Using Analog Means

February 22, 2023 by 13 Comments

Generating interesting imagery on an analog oscilloscope is a fun activity enjoyed by many, with an excellent demonstration by [Henry Segerman] provided in a recent video which covers [Matthias Goerner]’s demonstration. Using the electron beam, shapes can be drawn onto the phosphor of the oscilloscope’s CRT — all without touching any digital circuitry. At the core are analog components like an operational amplifier integrator, multipliers and other elements.

With just a number of these simple components in a circuit, it’s possible to draw a wide variety of shapes, all by applying the appropriate trigonometric parameters. In addition to the drawing of shapes, it is also demonstrated how these analog signals can be used for an analog audio synthesizer, and finally the image displayed on the oscilloscope is captured on Kodak (Polaroid) instant film, making the entire generating, processing and capturing chain fully analog.

While we’d be the last to campaign against digital electronics, it is fascinating to consider just how much can be done with analog electronics and a bit of mathematics. We assume that everyone did pay attention during math classes, making this a perfect chance to use all that knowledge of trigonometry.

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OG DOOM Shows Off The Origins Of Multi-Monitor

February 7, 2023 by 13 Comments

We have a thing for DOOM, and we admit it. The source was released, and clever hackers have ported the engine to every system imaginable. It’s a right of passage, when hacking a machine, to run DOOM on it — be it a VoIP phone, or tractor. But the original 1993 release does have a few notable tricks, and there’s something to be said for recreating that experience on period hardware. And that’s what we’re covering today: [Tech Tangents] discovered DOOM’s multi-monitor support, and built a 4-computer cluster to show it off.

There is a catch, of course. DOOM 1.1 has the multi-monitor support, and under-the-hood, it works by running a copy of the game on individual computers, and controlling the drones over the network. As the game’s network code was updated for version 1.2, the multi-monitor feature was axed to make the network code easier to maintain. So, find a 1.1 shareware release, install it on a DOS machine with IPX drivers, and start each iteration with a -net flag. Use -left and -right to set the drones to the appropriate view. And that view is ninety degrees left and right.

Maybe not ideal, but at the time it was one of the first games to have any sort of multi-monitor support at all. Likely inspired by a commercial flight simulator setup. Either way, it’s a neat feature, and kudos to [Tech Tangents] for showing off this obscure feature of a beloved classic!

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