A Close Look At How Flip-Dot Displays Really Work

March 3, 2023 by Chris Lott 13 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.

Continue reading “A Close Look At How Flip-Dot Displays Really Work” →

Collection Of Old Films Rescued For Preservation

February 28, 2023 by Chris Lott 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.

Continue reading “Collection Of Old Films Rescued For Preservation” →

Deep Dive Into The HP ScantJet 4C

February 24, 2023 by Chris Lott 24 Comments

[Shelby] at Tech Tangents recently wrapped a project / obsession to obtain an old HP ScanJet 4C, get it running on a PC and put it through its paces. After after nearly five years, three scanners, and untold SCSI cards and drivers later, he finally succeeded. The first big problem was getting a working scanner. These don’t stand up well to shipping, and one arrived with broken mirrors. And when he finally got one that worked, sorting out SCSI controller and driver issues was surprisingly complicated, though ultimately successful.

The HP ScanJet 4C was introduced in 1995, and was notable for its scanning quality, its resolution ( 2400 DPI interpolated / 600 DPI optical ), and selling for under $1000. Except for replacement parts concerns, particularly the customized triphosphor fluorescent bulb assembly, it would still be a very competent scanner today. For this reason, [Shelby] will not be using it as his daily use scanner. Continue reading “Deep Dive Into The HP ScantJet 4C” →

Lo-Fi Tchaikovsky

February 22, 2023 by Chris Lott 4 Comments

[Kevin] over at Simple DIY ElectroMusic Projects recently upgraded his Lo-Fi Orchestra. To celebrate his 400th blog post, he programmed it to play Tchaikovsky’s 1812 Overture. Two Arduino Nanos, four Arduino Unos, four Raspberry Pi Picos, and one Raspberry Pi have joined the Lo-Fi Orchestra this year, conducted by a new Pico MIDI Splitter. Changes were made in every section of the orchestra except percussion. We are delighted that the Pringles tom and plastic tub bass drums remain, not to mention the usual assortment of cheap mixers, amps, and speakers.

Tchaikovsky’s score famously calls for some “instruments” not found in the typical orchestra — a battery of cannon and a carillon, for example. Therefore [Kevin] had to supplement the Lo-Fi Orchestra for this performance with extras — a JQ6500 MP3 module on clash cymbals, a bare metal MiniDexed Raspberry Pi playing the carillon, and a MCP4725 with a Lots-of-LEDs shield firing off cannon and fireworks, respectively.

Although slightly disappointed that the MCP4725 beat out Mr. Fireworks in the auditions, we do like the result. [Kevin] reports that the latest version is much more reliable and predictable, having eliminated various MIDI faults and electrical noise. It presents a stable platform for future musical presentations, a kind of on-demand Lo-Fi Orchestra jukebox, as he describes it. A detailed review of all the changes can be found in his explanatory blog post. Check out an earlier performance of Holst’s The Planets suite from our coverage back in 2021.

Continue reading “Lo-Fi Tchaikovsky” →

Laser Scanner Upgraded To Use PCB Motor

February 22, 2023 by Chris Lott 10 Comments

[Rik]’s Hexastorm laser scanner project originally used a discrete polygon mirror controller+motor module from Sharp to spin a prism. But the scanner head was a bit difficult to assemble and had a lot of messy wires. This has all been replaced by a single board featuring a PCB-printed motor, based on the work of [Carl Bugeja]. The results are promising so far — see video below the break.

Since the prism is not attached to anything, currently it will fall off if mounted in the intended vertical orientation. One of [Rik]’s next steps is to improve the mount’s design to constrain the spinning prism. The previous Sharp motor was specified to 21000 RPM, but was only driven to 2400 RPM in [Rik]’s first version. This new PCB motor spins at 2000 RPM in these tests, comparable to his previous experiments ( we’re not sure about the maximum RPM ).

See our original writeup from 2019 to review the goals of this project, and be sure to checkout details and documentation on the Hexastorm project page. To learn more about PCB motors, read our article about [Carl]’s first design and visit his Hackaday.io page. Thanks to [Jonathan Beri] for the tip.

Continue reading “Laser Scanner Upgraded To Use PCB Motor” →

Reverse Engineering The Apple Lightning Connector

February 22, 2023 by Chris Lott 6 Comments

A frequent contributor to the hacker community, [stacksmashing] has prepared an excellent instructional video on reverse engineering Apple’s Lighting connector proprietary protocol. The video begins by showing how to gain physical access to the signals and hooking them up to a logic analyzer. He then notes that the handshaking uses only a single signal and proposes that Apple isn’t going to re-invent the wheel (perhaps a risky assumption). Using a ChatGPT search, obligatory these days, we learn that Dallas Semiconductor / Microchip 1-wire is probably the protocol employed.

Which embedded single-wire busses exist that encode bits with different lengths of low and high signals?

At the basic level, 1-wire and protocols like Texas Instruments SDQ operate in a similar manner. It turns out that [stacksmashing] already wrote a SDQ analyzer module for the Saleae logic analyzer. Aided by this tool, he digs deeper and learns more about the kinds of messages and their contents. For example, upon being plugged in, the host system queries the accessory’s serial number, manufacturer, model number, and product description. Finally, he introduces the CRC reverse engineering tool reveng to determine which CRC polynomial and algorithm the protocol uses to frame each packet.

Even if you have no interest in Lightning cables, this video is a great tutorial on the types of things you need to do in order to make sense of an unknown communications protocol. Gather what information you can, make some educated guesses, observe the signals, revise your guesses, and repeat. In part two, [stacksmashing] will show how to build a homemade iPhone JTAG cable.

We wrote in more detail about cracking the Lightning interface back in 2015. The Lightning interface may have been a good solution in its day, foreshadowing some of the features we now have in USB-C. But its proprietary and closed nature meant it wasn’t used outside of the Apple ecosystem. With the proliferation and capabilities of USB-C, not to mention various legislative edicts, Lightning’s days seem numbered. Is the industry finally settling on one interface? Let us know your thoughts in the comments below.

Continue reading “Reverse Engineering The Apple Lightning Connector” →

Exploring The History Of EPROM In The Soviet Union

February 21, 2023 by Chris Lott 17 Comments

An article on the history of EPROMs in the Soviet Union by [Vladimir Yakovlev] over at The CPU Shack Museum caught our attention. It is part one of a series on the topic, and walks you through the earliest Soviet EPROMs families.

Early EPROM programmer using punched paper tape (Intel, Electronics Magazine 1971)

The first of which, from the 1970s, is the K505RR1 developed and manufactured in Kyiv, equivalent to the first-generation Intel 1702A. It could hold 2048 bits, organized as 256×8, and offered a whopping 20 reprogramming cycles and data retention of 5000 hours.

The narrative proceeds to introduce several subsequent generations, design facilities, manufacturing techniques, and representative chip examples. A few tidbits — unlike Western EPROMs, the Soviets managed to put quartz windows in plastic packages (see the KP573 family).

In addition to the common gray or white, they also used different terracotta colored ceramic packages. An odd ceramic flat-pack EPROM is shown, and also some EPROMs whose dies have been painted over and re-badged as OTP chips.

Intel began producing EPROMs in 1971 as reported by the inventor, Intel’s Dov Frohman-Bentchkowsky, in Electronics Magazine’s 10 May edition (pg 91). We learned, amongst other things, that the 1701 did not have a quartz window, but could still be erased by exposure to X-rays. A friendly word of warning — browsing electronics advertisements from 50 years ago can easily consume your entire morning.

Once the package is sealed, information can still be erased by exposing it to X radiation in excess of 5×10⁴ rads, a dose which is easily attainable with commercial X-ray generators.

To dig deeper, check out the CPU Shack’s write-up on the history of EPROMs in general, and a piece we wrote in 2014 about the history of home computers behind the Iron Curtain.