Bask In The Glory Of This 336 LED Digit Display

[Chris Combs] recently took the wraps off of an incredible art piece that he calls Road Ahead which uses 336 seven segment LED digits to create an absolutely gorgeous display. With a piece of smoked acrylic to slightly diffuse the orange glow of the LEDs, the end result has a distinctively retro look that we’d gladly spend all day staring at.

For those looking to dig a bit deeper, [Chris] has put together some very impressive documentation over on that goes into plenty of detail on how he designed and built this beauty. From the design of the PCBs that carry all of the 0.3″ SMD displays to the custom software running on the Raspberry Pi 3 that powers it, there’s no technical stone left unturned.

According to the build log, this is the second version of the display. The first one was housed in a rather attractive wooden enclosure, but as [Chris] explains, that was precisely the problem. He wanted something that looked cold and unfeeling as the nearly 340 digits flashed away with potentially ominous intent. So he ditched the wooden case for a powder coated steel one that looks more like the front panel of a mainframe than something you’d pick up at the craft store.

Another interesting point explained in the write-up is how the Python software is designed to treat the hardware as a contiguous graphical display rather than just an array of independent digits. Grayscale images can be reproduced on the by using PWM to adjust the brightness of each segment’s corresponding “pixel”; though admittedly it takes a bit of imagination to see the intended image with a resolution this low.

This project reminds us of the incredible LED hexdump display we saw not that long ago, down to the PWM trickery for squeezing “graphics” out of these exceptionally non-graphical elements. With any luck, perhaps these are the opening shots in an arms race to see who can build the largest array of multi-segment LED displays.

A Strange Display Gives Up Its Secrets

Providing a display for a project in 2020 is something of a done deal. Standard interfaces and off-the-shelf libraries for easily available and cheap modules mean that the hardest choice you’ll have to make about a display will probably relate to its colour. Three decades ago though this was not such a straightforward matter though, and having a display that was in any way complex would in varying proportion take a significant proportion of your processing time , and cost a fortune. [AnubisTTP] has an unusual display from that era, a four-digit LED dot matrix module, and the take of its reverse engineering makes for a fascinating read.

The LITEF 104267 was made in 1986, and is a hybrid circuit in a metal can with four clear windows , one positioned over each LED matrix. Inside are seven un-encapsulated chips alongside the LED matrices on a golf plated hybrid substrate. The chips themselves are not of a particularly high-density process, so some high-resolution photography was able to provide a good guess at their purpose. A set of shift registers drive the columns through buffers, while the rows are brought out to a set of parallel lines. Thus each column can be illuminated sequentially with data presented on the rows. It’s something that would have saved a designer of the day a few extra 74-series chips, though we are guessing at some significant cost.

This display may seem antiquated to us today, but it wasn’t the only option for 1980s designers. There’s one display driver from back then that’s very much still with us today.

Movie-Style Hacking With A Wall Of Glowing Hex

Over the years, the media has managed to throw together some pretty ridiculous visual depictions of computer hacking. But perhaps none have gone as far down the road of obfuscation as The Matrix, where the most experienced hackers are able to extract information from a display of cascading green glyphs like a cyberpunk version of reading tea leaves. It’s absolutely ridiculous, with zero basis in reality.

Well, maybe not anymore. Taking a page from these outlandish visions of hacking, [Erik Bosman] has constructed a dedicated hex dump display out of fourteen segment alphanumeric LEDs that looks like it could be pulled from a movie set. But make no mistake, it’s more than just a pretty face. By cleverly varying the brightness of the individual characters, he’s managed to make his so-called “hexboard” completely usable despite the fact that everything’s the same color.

While he says the project is not quite at 100% yet, he’s already released the firmware, computer-side software, and even the PCB design files for anyone who might want to build their own version. Though as you might imagine, it’s quite a tall order.

The display is broken up into segments holding eight Houkem-5421 LED modules apiece, each with its own STM32F030F4 and two TC7258E LED controllers. The bill of materials on this one is a bit intimidating, but when the end result look this good it’s hard to complain.

To build a somewhat smaller version that also features a more retro vibe, you might consider doing something similar by chaining together vintage LED “bubble” displays.

Chaining Together A 16×2 Bubble LED Display

We’ve recently noticed an uptick of interest in so-called “bubble displays”: vintage alphanumeric LEDs which are probably best remembered as being used in watches and calculators before the LCD took over. Today they’re available as surplus or even salvage for literally pennies, but unfortunately they only provide four or five characters to work with. Or rather they did, until [sjm4306] built a board that chains them into a 16×2 array.

For the princely sum of 71 cents each, [sjm4306] picked up ten HPDL-1414 displays, each capable of showing four characters. He then designed a PCB that would accept eight of the displays at once, and even thought ahead to use headers so they could be pulled out and swapped as needed. Of course mounting them is only half the battle, you still need to drive the things.

Each display has its own dedicated driver chip on board, but trying to address each one individually would take far too many pins. So [sjm4306] opted to use a trio of 74HC595 shift registers, allowing him to toggle the three dozen pins necessary over SPI from a microcontroller. He’s even written up a little library and some example code that you can grab on the project’s page.

Unfortunately, after all his hard work, tragedy struck. As these displays were a couple decades old given their date code, [sjm4306] thought he would clean them up with a bit of alcohol before their big video debut. But whatever plastic the clear panels are made of didn’t take kindly to the IPA, and they all shattered. They still work, but it’s definitely a quirk to keep in mind if you pick up some of these vintage displays to play with yourself.

In the past we’ve seen a much smaller PCB that allowed similar displays to more easily be interfaced with modern microcontrollers; perfect if you just want to bang out a few retro LED characters with a minimum of fuss.

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LED Driver Board Could Be Your Ticket To FPGA Development

Microcontrollers are a great way to learn about developing for embedded systems. However, once you outgrow their capabilities, FPGAs bring muscle that’s hard for even the fastest-clocked micros to match. If you’re doing anything with high-speed signals, loads of RAM, or something that requires lots of parallel calculation, you can’t go past FPGAs. Dev boards can be expensive, but there are alternatives. There’s a nifty project on Github trying to repurpose commodity hardware into a useful FPGA development platform.

Chubby75 is a project to reverse engineer the RV901T LED “Receiver Card”. This device is used to receive signals over Ethernet, and clock data out to large LED displays. This sort of work is highly processor intensive for microcontrollers, but a cinch for FPGAs to manage. The board packs a user-reprogrammable Spartan 6 FPGA, along with twin Gigabit Ethernet ports and 64MB of SDRAM. Thanks to the fact that its firmware is not locked down, it has the potential to be repurposed into all manner of other projects. The boards are available for under $30 USD, making them a prime target for thrifty hackers.

Thus far, the team have begun poring through the hardware documentation and are looking to develop a toolchain to allow the boards to be easily reprogrammed. With the right tools, these boards could be the next thing in cheap FPGAs, taking over when the Pano Logic thin clients become thin on the ground.

[Thanks to KAN for the tip!]

Visualizing LEDs For More Efficient Pin Packing

The archetypal “blink an LED” is a great starter project on any platform, but once the bug takes hold that quickly turns into an exploration of exactly how many LEDs a given microcontroller can drive. And that often leads to Charlieplexing. A quick search yields many copies of The Table describing how many LEDs can be driven by a given number of pins but that’s just the most rudimentary way to describe it. Way back in 2013 [M Rule] developed a clever trick to describe the number of LED matrices which can be driven by a Charlieplexed array of a given size that makes this process much more intuitive. The post may be old, but we promise the method is still fresh.

[M Rule] was specifically looking to drive those big, cheap single color LED matrices which are often used to make scrolling signs and the like. These parts are typically a matrix of LEDs with a row of common cathodes and one of common anodes. Internally they are completely dumb and can be driven by row/column scanning, or any other way a typical matrix can be controlled. The question is, given known matrix sizes, how many can be driven with a a number of Charlieplexed LED drive pins?

The first step is to visualize the 1D array of available pins as a 2D matrix, as seen to the right. Note each numbered pin is the same on the X and Y, thus the black exclusion zone of illegal drive pin combinations slicing across the graph (you can’t drive an LED connected to one pin twice). The trick, if one were to say it resides in a single place, would be titling the axis anode and cathode, representing two “orientations” the drive pins can be put in. With this diagram [M Rule] observed you can simply drop a matrix into the array. If it fits outside the exclusion zone, it can be driven by those pins!

To the left is what this looks like with two 8×8 matrices, one connected between pins 1-8 and 9-16, the other connected between 9-16 and 1-8. This isn’t terribly interesting, but the technique works just as well with single LEDs and any size matrix, including 7-segment displays. Plus as long as an element doesn’t overlap itself it can wrap around the edges leading to some wild visuals, like 14 RGB LEDs on seven pins to the right.

The most extreme examples are pretty exotic. Check out [M Rule]’s post for the crown jewel; 18 pins to drive six 5×7 modules, six 7-segment displays, 12 single LEDs, and 18 buttons!

If this color coded diagram seems familiar, you may be remembering [openmusiclabs]’ excellent diagram describing ways to scan many of buttons. Or our coverage of another trick of matrix topology by [M Rule] from a few weeks ago.

Make Your Own Old School LED Displays

We live in an era in which all manner of displays are cheap and readily available. A few dollars spent online can net you a two-line alphanumeric LCD, a graphical OLED screen, or all manner of other options. Years ago however, people made do with little monolithic LED devices. [sjm4306] wanted to recreate something similar, and got down to work (Youtube link, embedded below).

The resulting device uses 0603 sized SMD LEDs, soldered onto a tiny PCB. 20 LEDs are used per digit, which can display numbers 0-9 and letters A-F. The LEDs are laid out in a pattern similar to Hewlett-Packard designs from years past. This layout gives the numerals a more pleasant appearance compared to a more-classic 7-segment design. Several tricks are used to make the devices as compact as possible, such as putting vias in the LED pads. This is normally a poor design technique, but it helps save valuable space.

[sjm4306] has developed a breadboard model, and a more advanced version that has a pad on the rear to mount a PIC16F88 microcontroller directly. We look forward to seeing these modules developed further, and can imagine they’d prove useful in a variety of projects.

For reference, check out these Soviet-era 7-segment displays. Video after the break.

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