Electromechanical 7-Segment Display Is High Contrast Brilliance

January 13, 2025 by Lewin Day 10 Comments

The seven-segment display is most well known in LED form, but the concept isn’t tied to that format. You can build a seven-segment display out of moving parts, too. [tin-foil-hat] has achieved just that with a remarkably elegant design.

As you might expect, the build relies heavily on 3D-printed components—produced in white and black plastic to create a high-contrast display. It’s a simple choice that makes the display easy to read in a wide variety of lighting conditions, and far less fussy than toying with LEDs and diffusers and all that.

Actuation of each display segment is achieved electromagnetically. Effectively, each segment behaves like a flip dot, with the orientation controlled by energizing one of two electromagnets per segment. Controlling the electromagnets is an ESP32, which is hooked up to the various segments via a Darlington transistor array, with multiplexing used to minimize the number of IO pins required. A shift register was also employed to let the microcontroller easily drive four of these electromechanical digits.

It’s a simple build, well explained—and the final result is aesthetically pleasing. We’ve seen a few builds along these lines before, albeit using altogether different techniques. Lots of different techniques, in fact! Video after the break.

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A Simple Serial Display

January 9, 2023 by Matthew Carlson 11 Comments

Often with more “modern” complex protocols involving handshaking, token exchanges, and all the other hoops and whistles accompanying them, we forget how useful and powerful serial can be. In what might be a wonderful tribute to that, [Davide Gironi] created a simple AVR-powered 16-digit serial display.

It can display two numbers, and that’s it. A MAX7219 drives the display, and the brains are an ATmega8. It’s straightforward to send new values: a start byte, a CRC, the data to display, and an end byte. A CP2102 provides a UART to USB interface to connect to a host. An EEPROM helps it remember the last numbers shown. It supports positive, negative, and floating-point numbers.

This is a beautiful example of doing one thing and doing it well. The design is simple and allows it to be used for anything. You can show the current stock market price, the time for the next two trains for your commute, or whatever else you can think of. [Davide] included a schematic, code, and a 3d printed enclosure.

Perhaps the idea could be combined with a clever design for a single-motor seven-segment display.

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A personal computer drive bay with a glowing LED display

Turbo Button Pays Charming Homage To Early Personal Computers

November 3, 2022 by Chris Wilkinson 33 Comments

The PC turbo button and LED clock speed display were common features on early personal computers. Wanting to add a little retro chic to his modern battle-station, [Matthew Frost] assembled a charming and functional homage to the turbo button control panel.

In days past, this automotive nomenclature implied a performance boost when activated. Instead, ‘turbo mode’ would clock your x86 processor at its rated speed. Disabling ‘turbo’ would throttle the CPU, often all the way down to 4.77MHz. Inherited from the original IBM PC, some early computer programs relied on this specific clock speed, and would otherwise run too fast (or not at all) on faster hardware. PC marketing teams and engineers alike stopped including the turbo button and glowing clock speed numbers around the Pentium era.

This modern re-imagining of the turbo button uses an Arduino microcontroller, seven-segment display and tactile switches to emulate the look and feel of the original hardware. Instead of directly adjusting the CPU clock speed, hitting turbo switches between balanced and high-performance Windows power plans. The seven-segment display measures this clock speed in GHz to two decimal places. We’ll admit that it’s pretty satisfying to see those numbers inch higher when switching to turbo.

The rightmost button switches between measuring CPU speed, GPU utilization, network load and memory utilization, which improves on its original inspiration. The tubular key lock, also a common sight on early PCs, enables and disables networking for the entire system, which is great for keeping the kids off the ‘net (at least until they figure out how to remove the 5.25″ drive bay from the system and hot-wire the network adapter with a paperclip).

There are more details on the GitHub page, in case you want to build your own. This project could look especially fetching in PC sleeper builds, where new components are ‘hidden’ in old case hardware. And if this has made you feel nostalgic at all, you may want to hear our thoughts on why it’s all about the Pentiums.

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An electromechanical wall clock on a workbench, showing "8888"

Silent Stepper Motors Make Electromechanical Clock Fit For A Living Room

March 10, 2022 by Robin Kearey 13 Comments

Large mechanical seven-segment displays have a certain presence that you just don’t get in electronic screens. Part of this comes from the rather satisfying click-click-clack sound they make at every transition. Unfortunately, such a noise quickly becomes annoying in your living room; [David McDaid] therefore designed a silent electromechanical seven-segment clock that has all the presence of a mechanical display without the accompanying sound.

As [David] describes in a very comprehensive blog post, the key to this silent operation is to use stepper motors instead of servos, and to drive them using a TMC2208 stepper motor driver. This chip has a unique method of regulating the current that does not introduce mechanical vibrations inside the motor. A drawback compared to servos is the number of control wires required: with four wires going to each motor, cable management becomes a bit of an issue when you try to assemble four seven-segment displays.

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Three-Dimensional Design Yields Compact Seven-Segment Hex Displays

November 11, 2021 by Adam Zeloof 10 Comments

Computers, from the simplest to the most complex, aren’t very useful if they can’t provide feedback to a user. Whether that interface takes the form of a monitor, a speaker, or a simple LED, there’s almost always some kind of output. One of the most ubiquitous is the ever-present seven-segment display. They’re small, they’re easy to use, and, perhaps most important, they’re cheap.

While the displays themselves are relatively compact, they often require some sort of driver circuitry — something that translates a digit into voltage at the correct pins. These drivers can take up valuable space, especially on a breadboard, and can sometimes make using seven-segment displays cumbersome. Thankfully, [John Lonergan] has a great solution: driver boards that sit completely beneath the displays. His dual seven-segment hex display project was born out of necessity — he needed it for the breadboard CPU SPAM-1, which was getting a bit too bulky. Each module is two seven-segment displays atop a small PCB. Beneath the displays lives an 8-bit PIC microcontroller, which acts as a driver for both of the displays.

It’s so easy to restrict ourselves to thinking in two dimensions when working on electronic design — even designing multilayer PCBs often feels like working on several, distinct two-dimensional areas rather than one three-dimensional one. The concept of stacking components to save space, while fairly straightforward to implement, is a great example of the kind of problem-solving we love to see here at Hackaday. Of course, if you like the idea of 3D circuit design, you have to check out some of these incredible circuit sculptures we’ve featured in the past.

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Incandescent 7-Segment Displays Are Awesome

April 20, 2021 by Lewin Day 17 Comments

When we think of 7-segment displays as the ubiquitous LED devices that sprung into popularity in the 1970s. However, numbers have existed for a lot longer than that, and people have wanted to know what the numbers are for quite some time, too. Thus, a variety of technologies were used prior to the LED – such as these magnificent incandescent 7-segment displays shown off by [Fran Blanche].

The displays are basic in concept, but we imagine a little frustrating in execution. Electronics was tougher back in the days when valves needed huge voltages and even a basic numerical display drew a load of current. Built to industrial-grade specifications, they’re complete with a big heatsinking enclosure and rugged gold-plated connectors. [Fran] surmises that due to the likely military applications of such hardware, the filaments in the bulbs were likely built in such a way as to essentially last indefinitely. The glow of the individual segments has a unique look versus their LED siblings; free of hotspots and the usual tapered shape on each segment. Instead, the numerals are pleasingly slab-sided for a familiar-but-not-quite aesthetic.

[Fran] demonstrates the display running with a CD4511B BCD-to-7-segment decoder, hooked up with a bunch of 3904 power transistors to get the chip working with filament bulbs instead of LEDs. It’s a little fussy, but the displays run great with the hardware sorted.

We’d love to see these used on a very heavy ridiculous watch; nixies aren’t the only game in town after all. If you do happen to make one, be sure to let us know. Video after the break.

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Huge Seven Segment Display Made From Broken Glass

February 10, 2020 by Tom Nardi 12 Comments

A staple of consumer devices for decades, seven segment displays are arguably one of the most recognizable electronic components out there. So it’s probably no surprise they’re cheap and easy to source for our own projects. But that doesn’t mean there isn’t room for personal interpretation.

[MacCraiger] wanted to build a wall clock with the classic seven segment LED look, only his idea was to make it slightly larger than average. With RGB LED strips standing in for individual LEDs, scaling up the concept isn’t really a problem on a technical level; the tricky part is diffusing that many LEDs and achieving the orderly look of a real seven segment display.

All those segments perfectly cut out of a sheet of plywood come courtesy of a CNC router. Once the rectangles had been cut out, [MacCraiger] had to fill them with something that could soften up the light coming from the LEDs mounted behind them. He decided to break up a bunch of glass bottles into small chunks, lay them inside the segments, and then seal them in with a layer of clear epoxy. The final look is unique, almost as though the segments are blocks of ice.

At first glance the use of a Raspberry Pi Zero to control the LED strips might seem overkill, but as it turns out, [MacCraiger] has actually added in quite a bit of extra functionality. The purists might say it still could have been done with an ESP8266, but being able to toss some Python scripts on the Linux computer inside your clock certainly has its appeal.

The big feature is interoperability with Amazon’s Alexa. Once he tells the digital home assistant to set an alarm, the clock will switch over to a countdown display complete with digits that change color as the timer nears zero. He’s also written some code that slowly shifts the colors of the digits towards red as the month progresses, a great way to visualize at a glance how close you are to blowing past that end of the month deadline.

We’ve seen something of a run on custom multi-segment displays recently. Just last month we saw a clock that used some incredible 25-segment LED displays, complete with their own unique take on the on epoxy-filled diffusers.

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