IoT-ifying an Old LED Signboard

Scrolling LED signs were pretty keen back in the day, and now they’re pretty easy to come by on the cheap. Getting a signboard configured for IoT duty can be tricky, but as [kripthor] shows us, it’s not that bad as long as security isn’t your top concern and you can tweak a serial interface.

dec-16-2016-10-57-pm-edited[kripthor] chanced upon an Amplus AM03127 signboard that hails from the days when tri-color LEDs were the big thing. The unit came with a defunct remote thanks to leaking batteries, but a built-in serial interface offered a way to connect. Unfortunately, the RS-232 standard on the signboard wants both positive and negative voltages with respect to ground to represent the 1s and 0s, and that wouldn’t work with the ESP8266 [kripthor] was targeting. The ubiquitous MAX-232 transceiver was enlisted to convert logic levels to RS-232 signals and a small buck converter was added to power the ESP. A little scripting and the signboard is online and ready for use and abuse by the interwebz — [kripthor] says he’ll regret this, but we’re pleased with the way the first remote access turned out. Feel free to check out the live video feed and see what the current message is.

Personally, we don’t have much use for a signboard, but getting RS-232 devices working in the Arduino ecosystem is definitely a trick we’ll keep in mind. If asynchronous serial protocols aren’t your strong suit, you might want to check out this guide to what can go wrong by our own [Elliot Williams].

Dead-Bug Logic Probe in a Magic Marker

Logic probes are simple but handy tools that can be had for a couple of bucks. They may not be the sexiest pieces of test gear, nor the most versatile, but they have their place, and building your own logic probe is a great way to understand the tool’s strength and weaknesses.

[Jxnblk]’s take on the logic probe is based on a circuit by [Tony van Roon]. The design hearkens back to a simpler time and is based on components that would have been easy to pick up at any Radio Shack once upon a time. The logic section is centered on the venerable 7400 quad 2-input NAND gate in the classic 14-pin DIP format. The gates light separate LEDs for high and low logic levels, and a 555 timer chip in a one-shot configuration acts as a pulse stretcher to catch transients. The DIP packages lend themselves to quick and dirty “dead bug” construction, and the whole thing fits nicely into a discarded marking pen.


It’s a simple build and a nice form factor for a useful tool, but for an even slimmer package like an old syringe you’ll probably have to go with SMD components. And when you graduate from the simple logic probe, you might want to check out the capabilities of this smart probe.

Power For An Amstrad Spectrum

If you were an American child of the early 1980s then perhaps you were the owner of a Commodore 64, an Apple II, or maybe a TRS-80. On the other side of the Atlantic in the UK the American machines were on the market, but they mostly lost out in the hearts and minds of eager youngsters to a home-grown crop of 8-bit micros. Computer-obsessed British kids really wanted Acorn’s BBC Micro, but their parents were more likely to buy them the much cheaper Sinclair ZX Spectrum.

Sinclair Research was fronted by the serial electronic entrepreneur [Clive Sinclair], whose love of miniaturization and ingenious cost-cutting design sometimes stretched the abilities of his products to the limit. As the 8-bit boom faded later in the decade the company faltered, its computer range being snapped up by his great rival in British consumer electronics, [Alan Sugar]’s Amstrad.

The Amstrad Spectrums replaced the rubber and then shaky plastic keys of the Sinclair-era machines with something considerably more decent, added joystick ports and a choice of a built-in cassette deck or one of those odd 3″ floppy disk drives for which Amstrad seemed to be to only significant customer. For that they needed a more capable power supply offering a selection of rails, and it is this unit that concerns us today. [Drygol] had a friend with an Amstrad-made Sinclair 128K Spectrum +2 with a broken power supply. His solution was to wire in a supply retrieved from a small form factor PC that had all the requisite lines, and for safety he encased it in an improbably huge piece of heat shrink tubing.

Wiring a PSU to a DIN plug for a retro computer is not an exceptional piece of work in itself even if it’s tidily done and nice to see older hardware brought back to life. What makes this piece worth a look instead is the teardown of what is a slightly unusual footnote to the 8-bit home computer story. We’re shown the familiar Z80 and support chips with the Spectrum edge connector and modulator on a through-hole board with a piece of cutting edge tech for a 1980s home computer, a single SMD chip unusually mounted nestled in a hole cut in the board.

Amstrad eventually stopped making Spectrums in the early 1990s, having also tried the Sinclair name on a spectacularly awful PC-compatible home computer. [Clive Sinclair] continued to release electronic products over the following decades, including a portable computer, the last of his trademark miniature radio receivers, and an electric bicycle accessory. Amstrad continue to make computers to this day, and [Alan Sugar] has achieved fame of a different sort as host of the UK version of The Apprentice. He has not yet become Prime Minister.

We’ve featured another Amstrad Spectrum +2 losing its tape deck for a slimmer machine. On that note, the Spectrum wasn’t Amstrad’s only entry in the 8-bit market, and we’ve also shown you a compact clone of their CPC464. As for [Drygol], he’s featured here several times. His mass-restoration of Commodore 64s for instance, or bringing a broken Atari ST back from the dead.

Repairing Flex Circuits By Accident

A while ago, [drygol] was asked to repair a few old Amiga keyboards. The key switches worked fine, but in the past decade or two, the flexible PCB ribbon connector has been mistreated, and was in an unworkable, nonfunctional state. The fragile traces underneath the green epoxy coating were giving way, but [drygol] found a few cool ways to repair these flex cables.

The end of this keyboard cable was beyond repair, but the Commodore engineers were gracious enough to leave a bit of slack in this keyboard connector. After cutting off the most damaged section, [drygol] had a strip of plastic, a few copper traces, and a green coating that had to be removed. The first attempt to remove this green covering used methanol, but that didn’t work. The next chemical attempt was with an epoxy solvent that contained nasty chemicals. This was applied to the end of the flex cable, with the remainder of the cable masked off by Kapton. It worked remarkably well.

In removing the Kapton masking tape, [drygol] discovered this green film sticks better to Kapton than it does to copper and plastic. A mechanical solution was found, allowing these keyboard cables to be easily repaired.

Of course, this was only half of the problems with these flexible circuits. Over the years, a few cracks appeared in the traces. To repair these broken traces, [drygol] turned to silver glue and a few laminations of Kapton to make this keyboard cable whole again. It worked, and the ancient keyboard was returned to service. Great work, and a fantastic observation for anyone with one of these keyboards sitting around: just grab a roll of Kapton to repair these circuits. It can’t get any easier than that.

Portable Apple II On An AVR

The Apple II was one of the first home computers. Designed by Steve “Woz” Wozniak, it used the MOS technologies 6502 processor, an 8-bit processor running at about 1 MHz. [Maxstaunch] wrote his bachelor thesis about emulating the 6502 in software on an AVR1284 and came up with a handheld prototype Apple II with screen and keyboard.

Prototype on veroboard

Originally, [maxstrauch] wanted to build an NES, which uses the same 6502 processor, but he calculated the NES’s Picture Processing Unit would be too complicated for the AVR, so he started on emulating the Apple II instead. It’s not quite there – it can only reference 12K of memory instead of the 64K on the original, so hi-res graphic mode, and therefore, many games, won’t work, but lo-res mode works as well as BASIC (both Integer BASIC and Applesoft BASIC.)

[Maxstrauch] details the 6502 in his thesis and, in a separate document, he gives an overview of the project. A third document has the schematic he used to build his emulator. His thesis goes into great detail about the 6502 and how he maps it to the AVR microcontroller. The build itself is pretty impressive, too. Done on veroboard, the build has a display, keyboard and a small speaker as well as a micro SD card for reading and storing data. For more 6502 projects, check out the Dis-Integrated 6502 and also, this guide to building a homebrew 6502.

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Character Generation in 144 Bytes

[Jaromir Sukuba]  has an awesome BrainF*ck interpreter project going. He’s handling the entire language in less than 1 kB of code. Sounds like a great entry in the 1 kB Challenge. The only problem is the user interface. The original design used a 4 line character based LCD. The HD44780 controller in these LCDs have their own character table ROM, which takes up more than 1 kB of space alone.

[Jaromir] could have submitted the BrainF*ck interpreter without the LCD, and probably would have done well in the contest. That wasn’t quite enough for him though. He knew he could get character based output going within the rules of the contest. The solution was a bit of creative compression.

bf-cs-3Rather than a pixel-by-pixel representation of the characters, [Jaromir] created a palette of 16 single byte vectors of commonly used patterns. Characters are created by combining these vectors. Each character is 4 x 8 pixels, so 4 vectors are used per character. The hard part was picking commonly used bit patterns for the vectors.

The first iteration was quite promising – the text was generally readable, but a few characters were pretty bad. [Jaromir] kept at it, reducing and optimizing his vector pallet twice more. The final design is pretty darn good. Each character uses 16 bits of storage (four 4-bit vector lookup values). The vector pallet itself uses 16 bytes. That means 64 characters only eat up 144 Bytes of flash.
This is exactly the kind of hack we were hoping to see in the 1 kB challenge. A bit of creative thinking finds a way around a seemingly impossible barrier. The best part of all is that [Jaromir] has documented his work, so now anyone can use it in the 1 kB challenge and beyond.



If you have a cool project in mind, there is still plenty of time to enter the 1 kB Challenge! Deadline is January 5, so check it out and fire up your assemblers!


High-Quality Film Transfers with this Raspberry Pi Frame Grabber

Untold miles of film were shot by amateur filmmakers in the days before YouTube, iPhones, and even the lowly VHS camcorder. A lot of that footage remains to be discovered in attics and on the top shelves of closets, and when you find that trove of precious family memories, you’ll be glad to have this Raspberry Pi enabled frame-by-frame film digitizer at your disposal.

With a spare Super 8mm projector and a Raspberry Pi sitting around, [Joe Herman] figured he had the makings of a good way to preserve his grandfather’s old films. The secret of high-quality film transfers is a frame-by-frame capture, so [Joe] set about a thorough gutting of the projector. The original motor was scrapped in favor of one with better speed control, a magnet and reed switch were added to the driveshaft to synchronize exposures with each frame, and the optics were reversed with the Pi’s camera mounted internally and the LED light source on the outside. To deal with the high dynamic range of the source material, [Joe] wrote Python scripts to capture each frame at multiple exposures and combine the images with OpenCV. Everything is stitched together later with FFmpeg, and the results are pretty stunning if the video below is any indication.

We saw a similar frame-by-frame grabber build a few years ago, but [Joe]’s setup is nicely integrated into the old projector, and really seems to be doing the job — half a million frames of family history and counting.

Continue reading “High-Quality Film Transfers with this Raspberry Pi Frame Grabber”