When choosing a low-level language, it’s hard to beat the efficiency of Forth while also maintaining some amount of readability. There are open source options for the language which makes it accessible, and it maintains its prevalence in astronomical and other embedded systems for its direct hardware control and streamlined use of limited resources even though the language started over 50 years ago. Unlike 50 years ago, though, you can now take your own self-contained Forth programmer on the go with you.

The small computer is built on a design that [Dennis] built a while back called my4TH which has its own dedicated 8-bit CPU and can store data in a 256 kB EEPROM chip. Everything else needed for the computer is built in as well but that original design didn’t include a few features that this one adds, most notably a small 40×4 character LCD and a keyboard. The build also adds a case to tie everything together, with ports on the back for I2C and power plus an RS232 port. An optional battery circuit lets the computer power up without an external power supply as well.

Part of the appeal of Forth for systems like this is that it includes an interpreter and compiler in addition to the programming language itself, meaning that it has everything needed for a usable computer system built right in. For some more details on this unique language, or if you’d like to explore below the world of Python or C, check out [Elliot]’s discussion on the “hacker’s language.”. While Forth can tackle big problems, it can fit on tiny machines, too.

Displays are crucial to modern life; they are literally everywhere. But modern flat-panel LCDs and cheap 7-segment LED displays are, well, a bit boring. When we hackers want to display the progress of time, we want something more interesting, hence the plethora of projects using Nixie tubes and various incantations of edge-lit segmented units. Here is [upir] with their take on the simple edge-lit acrylic 7-segment design, with a great video explanation of all the steps involved.

The idea behind this concept is not new. Older displays of this type used tiny tungsten filament bulbs and complex light paths to direct light to the front of the display. The modern version, however, uses edge-lit panels with a grid of small LEDs beneath each segment, which are concealed within a casing. This design relies on the principle of total internal reflection, created by the contrast in refractive indices of acrylic and air. Light entering the panel from below at an angle greater than 42 degrees from normal is entirely reflected inside the panel. Fortunately, tiny LEDs have a wide dispersion angle, so if they are positioned close enough to the edge, they can guide sufficient light into the panel. Once this setup is in place, the surface can be etched or engraved using a CNC machine or a laser cutter. A rough surface texture is vital for this process, as it disrupts some of the light paths, scattering and directing some of it sideways to the viewer. Finally, to create your display, design enough parallel-stacked sheets for each segment of the display—seven in this case, but you could add more, such as an eighth for a decimal point.

How you arrange your lighting is up to you, but [upir] uses an off-the-shelf ESP32-S3 addressable LED array. This design has a few shortcomings, but it is a great start—if a little overkill for a single digit! Using some straightforward Arduino code, one display row is set to white to guide light into a single-segment sheet. To form a complete digital, you illuminate the appropriate combination of sheets. To engrave the sheets, [upir] wanted to use a laser cutter but was put off by the cost. A CNC 3018 was considered, but the choice was bewildering, so they just went with a hand-engraving pick, using a couple of 3D printed stencils as a guide. A sheet holder and light masking arrangement were created in Fusion 360, which was extended into a box to enclose the LED array, which could then be 3D printed.

If you fancy an edge-lit clock (you know you do) check out this one. If wearables are more your thing, there’s also this one. Finally, etched acrylic isn’t anywhere near as good as glass, so if you’ve got a vinyl cutter to hand, this simple method is an option.

Morse code, often referred to as continuous wave (CW) in radio circles, has been gradually falling out of use for a long time now. At least in the United States, ham radio licensees don’t have to learn it anymore, and the US Coast Guard stopped using it even for emergencies in 1999. It does have few niche use cases, though, as it requires an extremely narrow bandwidth and a low amount of power to get a signal out and a human operator can usually distinguish it even if the signal is very close to the noise floor. So if you want to try and learn it, you might want to try something like this Morse trainer from [mircemk].

While learning CW can be quite tedious, as [mircemk] puts it, it’s actually fairly easy for a computer to understand and translate so not a lot of specialized equipment is needed. This build is based around the Arduino Nano which is more than up for the job. It can accept input from any audio source, allowing it to translate radio transmissions in real time, and can also be connected to a paddle or key to be used as a trainer for learning the code. It’s also able to count the words-per-minute rate of whatever it hears and display it on a small LCD at the front of the unit which also handles displaying the translations of the Morse code.

If you need a trainer that’s more compact for on-the-go CW, though, take a look at this wearable Morse code device based on the M5StickC Plus instead.

While we aren’t typically put off by a large wristwatch, we were taken a bit aback by [Chris Fenton]’s latest timepiece — if you can call it that. It’s actually a 1/25th-scale Cray C90 worn as a wristwatch. The whole thing started with [Chris] trying to build a Cray in Verilog. He started with a Cray-1 but then moved to a Cray X-MP, which is essentially a Cray-1 with two extra address bits. Then he expanded it to 32 bits, which makes it a Cray Y-MP/C90/J90 core. As he puts it, “If you wanted something practical, go read someone else’s blog.”

The watch emulates a Cray C916 and uses a round OLED display on the top. While the move from 22 to 32 address bits sounds outdated, keep in mind the Cray addresses 64-bit words exclusively, so we’re talking access to 32 gigabytes of memory. The hardware consists of an off-the-shelf FPGA board and a Teensy microcontroller to handle mundane tasks like driving the OLED display and booting the main CPU. Interestingly, the actual Cray 1A used Data General computers for a similar task.

Of course, any supercomputer needs a super program, so [Chris] uses the screen to display a full simulation of Jupiter and 63 of its moons. The Cray excels at programs like this because of its vector processing abilities. The whole program is 127 words long and sustains 40 MFLOPs. Of course, that means to read the current time, you need to know where Jupiter’s moons are at all times so you can match it with the display. He did warn us this would not be practical.

While the Cray wouldn’t qualify as a supercomputer today, we love learning about what was state-of-the-art not that long ago. Cray was named, of course, after [Seymour Cray] who had earlier designed the Univac 1103, several iconic CDC computers, and the Cray computers, of course.

The Frame AR glasses by Brilliant Labs, which contain a small display, are an entirely different approach to hacker-accessible and affordable AR glasses. [Karl Guttag] has shared his thoughts and analysis of how the Frame glasses work and are constructed, as usual leveraging his long years of industry experience as he analyzes consumer display devices.

It’s often said that in engineering, everything is a tradeoff. This is especially apparent in products like near-eye displays, and [Karl] discusses the Frame glasses’ tradeoffs while comparing and contrasting them with the choices other designs have made. He delves into the optical architecture, explaining its impact on the user experience and the different challenges of different optical designs.

The Frame glasses are Brilliant Labs’ second product with their first being the Monocle, an unusual and inventive sort of self-contained clip-on unit. Monocle’s hacker-accessible design and documentation really impressed us, and there’s a pretty clear lineage from Monocle to Frame as products. Frame are essentially a pair of glasses that incorporate a Monocle into one of the lenses, aiming to be able to act as a set of AI-empowered prescription glasses that include a small display.

We recommend reading the entire article for a full roundup, but the short version is that it looks like many of Frame’s design choices prioritize a functional device with low cost, low weight, using non-specialized and economical hardware and parts. This brings some disadvantages, such as a visible “eye glow” from the front due to display architecture, a visible seam between optical elements, and limited display brightness due to the optical setup. That being said, they aim to be hacker-accessible and open source, and are reasonably priced at 349 USD. If Monocle intrigued you, Frame seems to have many of the same bones.

We would not be surprised if DSI screens made up the majority of screens on our planet at this moment in time. If you own a smartphone, there’s a 99.9% chance its screen is DSI. Tablets are likely to use DSI too, unless it’s eDP instead, and a smartwatch of yours definitely will. In a way, DSI displays are inescapable.

This is for a good reason. The DSI interface is a mainstay in SoCs and mobile CPUs worth their salt, it allows for higher speeds and thus higher resolutions than SPI ever could achieve, comparably few pins, an ability to send commands to the display’s controller unlike LVDS or eDP, and staying low power while doing all of it.

There’s money and power in hacking on DSI – an ability to equip your devices with screens that can’t be reused otherwise, building cooler and cooler stuff, tapping into sources of cheap phone displays. What’s more, it’s a comparably underexplored field, too. Let’s waste no time, then!

Decently Similar Internals

DSI is an interface defined by the MIPI Alliance, a group whose standards are not entirely open. Still, nothing is truly new under the sun, and DSI shares a lot of concepts with interfaces we’re used to. For a start, if you remember DisplayPort internals, there are similarities. When it comes to data lanes, DSI can have one, two or four lanes of a high-speed data stream; smaller displays can subsist with a single-lane, while very high resolution displays will want all four. This is where the similarities end. There’s no AUX to talk to the display controller, though – instead, the data lanes switch between two modes.

The first mode is low-speed, used for sending commands to the display, like initialization sequences, tweaking the controller parameters, or entering sleep mode. You can capture this with a logic analyzer. If you’ve ever sniffed communications of an SPI display, you will find that there are many similarities with how DSI commands are sent – in fact, many SPI displays use a command set defined by the MIPI Alliance that DSI displays also use. (If your Sigrok install lists a DSI decoder, don’t celebrate too soon – it’s an entirely different kind of DSI.)

The second mode is high-speed, and it’s the one typically used for pixel transfer. A logic analyzer won’t do here, at least not unless it’s seriously powerful when it comes to capture rate. You will want to use a decent scope for working with high-speed DSI signals, know your way around triggers, and perhaps make a custom PCB tap with a buffer for the the DSI signal so that your probe doesn’t become a giant stub, and figure out a way to work with the impedance discontinuities. Still, it is very much possible to tap into high-speed DSI, like [Wenting Zhang] has recently demonstrated, sometimes an approximation of the high-speed signal is more than enough for reverse-engineering.

Got a datasheet for your panel? Be careful – the initialization sequence in it might be wrong; if your bringup is not successful or your resulting image is weird, this just might be the culprit, so even if you have procured the correct PDF, you might still end up having to capture the init sequence with a logic analyzer. Whether your display’s initialization are well-known, or you end up capturing them from a known-working device, you will need something to drive your display with – a typical Arduino board will no longer do; though, who knows, an RP2040 just might, having seen what you all are capable of.

Ideally, you will want a microcontroller or a CPU that has a DSI peripheral, with decent documentation and/or examples on how to use it – that part is important. Linux-capable Raspberry Pi boards can help you here a surprising amount – you may remember the Raspberry Pi DSI header as being proprietary, but that was only true initially. With developments like the official Raspberry Pi screen and open-source graphics drivers aided by that $10k driver bounty they put out, it became viable to connect custom screens. WaveShare DSI screens are a known alternative if you want to get a DSI display for your Pi. On the regular Pi, you only get two lanes of DSI, but that is good enough for many a display. Funnily enough, you can get a third-party display for your Pi that uses the same panel, with two extra chips that seem to run the display without a driver like the official Pi display (this thread on these displays is fascinating!); the display is still limited to the same resolution, the only advantage is a slightly lower price, and the ability to overload your 3.3V rail is a questionable benefit. It’s not quite clear why this display exists, but you might want to resist the temptation.

If you’re using a Pi Compute Module, you get entire two DSI peripherals to play with, one four-lane and one two-lane, and it doesn’t take long to find a good few examples of Raspberry Pi Compute Module boards with DSI screens. If you have a Compute Module and its devboard somewhere on a shelf, you can do four-lane DSI, with a Linux-exposed interface that works in the same way alternative OSes do on your phone. Given that CMs are typically used for custom stuff and a hacker using one is more likely to have patience for figuring out DSI panel parameters, a Compute Module baseboard is a pretty popular option to hack on that one cheap DSI display from a tablet that caught your eye! Don’t have a baseboard? You can even etch one, here’s a single-layer breakout with a DSI socket. Not that you don’t need a Compute Module if you’re doing two-lane DSI: a regular Pi will do.

So, get out there and hack – there is a ton of unexplored potential in the never-ending supply of aftermarket screens for older iPhone and Samsung models!  Speaking of phones, they are the forefront of DSI hacking, as you might suspect, thanks to all the alternative OS projects and Linux kernel mainlining efforts. You can enjoy fruits of their labour fairly easily, sparing you a logic analyzer foray – reusing a seriously nice DSI display might be as easy as loading a kernel module.

Want A Panel? Linux Is Here To Help

There’s a fun hacker tactic – if you’re looking for an I2C GPIO expander chip, you can scroll through the Linux kernel config file that lists supported GPIO expanders, and find a good few ICs you’ve never known about! What’s great is, you know you’re getting a driver, too.

The same goes for DSI screens, except the payoff is way higher. If you’re on the market for a DSI screen, you can open the list of Linux kernel drivers for various DSI panels. Chances are, all you need is just the physical wireup part, maybe some backlight driving, and a Device Tree snippet.

Want a $20 1920 x 1200 IPS display for your Compute Module? Who doesn’t! Well, wouldn’t you know, the Google Nexus 7 tablet uses one, and the driver for it is in mainline Linux! Just solder together a small FPC-to-bespoke-connector adapter board (or order PCBA), add a Device Tree snippet into your configuration, and off you go; there are even custom boards for using this display with a CM4, it’s that nice.

New displays get added into the kernel all the time; all it takes is someone willing to poke at the original firmware, perhaps load a proprietary kernel module into Ghidra and pull out the initialization sequence, or simply enable the right kind of debug logging in the stock firmware. All of this is thanks to tireless efforts of people trying to make their phones work beyond the bloatware-ridden shackles of the stock Android OS; sometimes, it’s some company doing the right thing and upstreaming a driver for a panel used by hundreds of thousands of devices in the wild.

There are some fun nuances in the display scene, as much as of a “scene” it is – people are just trying to make their devices work for them, then share that work with other people in the same situation, figuring out a display is part of the process. It’s not uncommon that a smartphone will use slightly different screens in the same batch – it’s an uncommon but real issue with alternative OSes like LineageOS, where, say, 10% of your firmware’s users might have their panel malfunction because, despite the phone listing the same model on the lid, their specific phones use a display with a different controller, that only the manufacturer’s firmware properly accounts for.

Our DSI Role Models

These are the basics of what you need to reuse DSI displays as if effortlessly. Now, I’d like to highlight a good few examples of people hacking on DSI, from our coverage and otherwise.

Without a doubt, the first one that springs to mind is [Mike Harrison] aka [mikeselectricstuff], from way back in 2013. I’ve spent a lot of time with the exact iPod Nano being reverse-engineered, and [Mike]’s videos gave me insight into a piece of tech I relied on for a fair bit. For instance, in this video, [Mike] masterfully builds a scoping jig, solders microscoping wires to the tiny PCB, walks us through the entire reverse-engineering process, and successfully reuses the LCD for a project.

Following in [Mike]’s footsteps, we’ve even seen this display reused in an ESP32 project, thanks to a parallel RGB to DSI converter chip!

[Wenting Zhang] reverse-engineering a Macbook Touchbar display is definitely on my favourites list. In this short video, he teaches us DSI fundamentals, and manages to show the entire reverse-engineering process from start to end., no detail spared. Having just checked the video description, the code is open-source, and it’s indeed a RP2040 project – just like I forecasted a good few paragraphs above.

Are mysterious ASICs your vibe, and would you like to poke at some firmware? You should see this HDMI-to-DSI adapter project, then. The creator even turns it into a powerbank with a built-in screen as a demo – that’s a hacker accessory if I’ve ever seen one. More of a gateware fan? Here’s an FPGA board doing the same, and another one, that you can see here driving a Galaxy S4 screen effortlessly. Oh, and if you are friends with a Xilinx+Vivado combination, there are DSI IP cores for you to use with barely any restrictions.

The Year Of DSI Hacking

DSI is an interface that is becoming increasingly hacker-friendly – the economies of scale are simply forcing our hand, and even the microcontroller makers are following suit. The official devboard for Espressif’s ESP32-P4, a pretty beefy RISC-V chip, sports a DPI interface alongside the now-usual CSI for cameras. We will see DSI more and more, and I raise a glass of water for numerous hackers soon to reap the fields of DSI. May your harvest be plentiful.

I thank [timonsku] for help with this article!

If there’s one thing we like better around here than old, obscure displays, it’s old, obscure displays with no documentation that need a healthy dose of reverse engineering before they can be put to use. These Plessey dot-matrix displays are a perfect example of that.

We’re not sure where [Michael] scored these displays, but they look fantastic. Each 8-pin DIP has two 5×7-matrix, high-visibility LED displays. They bear date codes from the late 80s under the part number, GPD340, but sadly, precious little data about them could be dredged up from the Interwebz. With 70 pixels and only six pins after accounting for power and ground, [Michael] figured there would be a serial protocol involved, but which pins?

He decided to brute-force the process of locating them, using a Pico to sequentially drive every combination while monitoring the current used with a current sensor. This paid off after only a few minutes, revealing that each character of the display has its own clock and data pins. The protocol is simple: pull the clock and data pins high then send 35 bits, which the display sorts out and lights the corresponding pixels. The video below shows a 12-character scrolling display in action.

Plessey made a lot of displays for military hardware, and these chunky little modules certainly have a martial air about them. Given that and the date code, these might have come from a Cold War-era bit of military hardware, like this Howitzer data display which sports another Plessey-made display.

Unique clocks are a mainstay around here, and while plenty are “human readable” without any instruction, there are a few that take a bit of practice before someone can glean the current time from them. Word clocks are perhaps on the easier side of non-traditional displays but at the other end are binary clocks or even things like QR code clocks. To get the best of both worlds, though, multiple clock faces can be combined into one large display like this clock build from [imitche3].

The clock is actually three clocks in one. The first was inspired by a binary clock originally found in a kit, which has separate binary “digits” for hour, minute, and second and retains the MAX 7219 LED controller driving the display. A standard analog clock rests at the top, and a third clock called a retrograde clock sits at the bottom with three voltmeters that read out the time in steps. Everything is controlled by an Arduino Nano with the reliable DS3231 keeping track of time. The case can be laser-cut or 3D printed and [imitche3] has provided schematics for both options.

As far as clocks builds go, we always appreciate something which can be used to tell the time without needing any legends, codes, or specialized knowledge. Of course, if you want to take a more complex or difficult clock face some of the ones we’re partial to are this QR code clock which needs a piece of hardware to tell the time that probably already has its own clock on it.

[Felipe Tavares] wasn’t satisfied with the boring default fonts on an HD44780-based display. And while you can play some clever tricks with user-defined characters, if you want to treat the display as an array of pixels, you’ve got to get out your scalpel and cut up a data line.

The hack builds on work from [MisterHW] who documented the bits going from the common display driver to the display, and suggested that by cutting the data line and sending your own bits, you could send arbitrary graphics. The trick was to make sure that they’re in sync with the display, though, which means reading the frame sync line in user code.

This done, it looks like [Felipe] has it working! If you can read Rust for the ESP32, he has even provided us with a working demo of the code that makes it work.

We can’t help but wonder if it’s not possible to go even lower-level and omit the HD44780 entirely. Has anyone tried driving one of these little LCD displays directly from a microcontroller, essentially implementing the HD44780 yourself?

Any way you slice it, this is a cool hack, and it opens up the doors to DOOM, or as [MisterHW] suggests, Bad Apple on these little displays . If you do it, we want to see it.

If your needs aren’t so exotic, the classic HD44780 display is a piece of cake to get working, and an invaluable tool in anyone’s toolbox.

[Jens] wanted a subscriber counter for his YouTube channel. He could have gone with a simple OLED, LCD, or LED display, but he wanted something more tactile and interesting. So he built a mechanical 7-segment display instead!

Currently, [Jens]’s channel is in the four-digit subscriber range, so he planned to build a four-digit display. He started by searching for existing projects in this space, and came across the designs of [shiura] on Thingiverse. [shiura] had a 3D printed cam-driven 7-segment digit that runs on a single servo motor. Once armed with four of the digits, he hooked them up to a Pi Pico W to drive them all with four servo outputs. The Pico W is responsible for querying the channel subscriber count online, and updating the display in turn.

It’s a neat build, and [Jens] learned some things along the way—like how Super Lube seemed to ruin filament for him. Ultimately, the build came good, and it looks great. We’ve seen some other mechanical 7-segment builds before, too!

While split-flap alarm clocks once adorned heavy wood nightstands in strong numbers, today the displays are most commonly found in train stations and airports. Hey, at least they’re still around, right? Like many of us, [The Wrench] has always wanted to make one for themselves, but they actually got around to doing it.

This doesn’t seem like a beginner-friendly project, but [The Wrench] says they were a novice in 3D design and so used Tinkercad to design all the parts. After so many failures, they settled on a design for each unit that uses a spool to attach the flaps, which is turned by a stepper motor.

A small neodymium magnet embedded in the primary gear and a Hall effect sensor determine where the stepper motor is, and in turn, which number is displayed. Everything is handled by an Arduino Nano on a custom PCB.

Aside from the sleek, minimalist look, our favorite part is that [The Wrench] used even more magnets to connect each display segment to the base. You may have noticed that there are only three segments, because the hours are handled by a single display that has flaps for 10, 11, and 12. This makes things simpler and gives the clock an interesting look. Be sure to check out the build video after the break.

Want to build a more complicated clock? Try suspending sand digits in the air with persistence of vision.

With the demands of modern computing, from video editing, streaming, and gaming, many of us will turn to a monitoring system of some point to keep tabs on CPU usage, temperatures, memory, and other physical states of our machines. Most are going to simply display on the screen but this data can be sent to external CPU monitors as well. This retro-styled monitor built on analog voltmeters does a great job of this and adds some flair to a modern workstation as well.

The build, known as bbMonitor, is based on the ESP32 platform which controls an array of voltmeters via PWM. The voltmeters have been modified with a percentage display to show things like CPU use percentage. Software running on the computers sends this data in real time to the ESP32 so the computer’s behavior can be viewed at a glance. Each voltmeter is also augmented with RGB LEDs that change color from green to red as use increases as well. The project’s creator, [Corebb], also notes that the gauges will bounce around if the computer is under heavy load but act more linearly when under constant load, also helping to keep an eye on computer status.

While the build does seem to rely on a Windows machine to run the software for export to the monitor, all of the code is open-sourced and available on the project’s GitHub page and could potentially be adapted for other operating systems. And, as far as the voltmeters themselves go, there have been similar projects in the past that use stepper motors as a CPU usage monitor instead.