Let's Build a Mechanical 7-Segment Display (video, 14m)

This is a seven-segment display. We are surrounded by them every day, but they all share one common weakness, their reliance on power. So I set out to design a mechanical display that retains its information even without power. In theory, this project shouldn't be too hard. All I need are seven colored strips that I can control electronically. And it turns out people have already done this, so it should be simple, right? Well, not really. Whilst these displays are super cool, there are a few flaws with them. Some require manual inputs, whilst others require extremely complex controlling circuitry. And others have design limitations. Take this mechanical display invented by Jay from Ingenisi. It uses mechanical cams to push out flaps to display digits. And this allows you to predefine the sequence needed for each number you wish to display. That means when displaying a zero from nine, you need to iterate through every other number. Not only that, but it means you can't display letters. And there are a few commercial ones still available. But due to them being vintage, well, I can't afford them. So why not make my own? How hard could it be? Traditionally, the way that these displays work is that they use seven segments that can light up individually to therefore display a bunch of numbers and letters. Well, eight if you include the decimal. This allows you to easily display numbers in both binary and hexadecimal, as well as some basic words. But these displays use little lights. And it's 2025. And that means it's the perfect time to over-engineer something. My first thought was to raise or lower sections so that it appears as if a number or letter is being displayed. But when viewed from the front, you can't tell which ones have been raised or lowered, meaning that the display is only useful when viewed from the side. We want this display to be easily visible, even from far. And I remembered this really cool video I saw a while back about something called a flip-dot. The way flip-dots work is by using tiny magnets you can electronically switch on or off. This means that you can repel a permanent magnet that is fixed on the dot, making it flip over. This allows you to quickly flip between two colors and thus display images. The issue is professional flip-dots have some magic ceramic core, which allows the electromagnet to retain its magnetism even once the power has been removed. But then I stumbled across some 3D-printed flip-dots by Larry Bills. And this got me thinking. Could I design a flip-dot that was shaped like one of the seven segments of a seven-segment display by simply using a bolt and some 3D-printed parts? The advantage is when power is not applied, the magnet is still attracted to the iron in the bolt, helping it retain its position. The reason any of this works is because when a current is passed through a wire, it generates a small magnetic field, which means when you wrap a bunch of wires around an iron core, their fields compound and turn the iron into a temporary magnet. This is similar to an experiment you might have done when you were younger, where you can rub a magnet over a piece of iron and turn it into a temporary magnet. What it's doing is it's aligning domains, or small magnetic poles within the iron, into the same direction, allowing it to act as a magnet. However, the advantage of an electromagnet is that by reversing the current, you can also reverse the polarity of the magnet. Circuits that flip current start to get more complex, and more importantly, expensive. And remember, we need seven of these per digit. We can get around this by using two electromagnets. This allows us to have a constant direction of current and just repel the permanent magnet based on which electromagnet it's closest to. Now, I just have to replicate this process six more times, which transforms a single flap, or segment, into a full seven segment mechanical display. I also designed a case, as well as room for all 14 electromagnets, and a custom circuit board. Time to print out some flaps and assemble a digit. After putting the two flat pieces together and pushing in the magnet, we can snap them into the center panel and make sure they rotate freely. Then we can fill in those gaps with some front panels. And since I've bought the wrong length bolts, I have to do a bit of welding. These will make up the cores of our electromagnets. To help keep everything in place, I then push on some 3D printed spools. I quickly got sick of winding these by hand, and so opted to build myself a little electromagnet spooler. The resistance of these coils is super important. Then it's time to put everything together. So far, nothing is broken, which is great. Although these wires are starting to get a little bit out of hand. So I think it's about time to try and make a custom PCB. We'll need one as a main controller, and one in the back of every digit to help connect all the electromagnets. And done, just like that. A quick check in 3D to see how it's all going to look, and I'm pretty happy with the results. It's all going to look, and I'm pretty happy with that. So now it's time to export the Gerber files and take them to my CNC. But then I realized, I have no idea how to use this thing. For a start, it uses an SD card, not a USB. And I'm completely terrified, because, well, I built it. If only there was someone that could make them for me, someone like PCBWay. PCBWay is an all-in-one PCB manufacturing company. They allow engineers and makers to have custom circuit boards made at a professional quality and for an affordable price. Not only that, but they provide stencils and can assemble your circuit boards for you. Once you've placed your order and uploaded your files, you can easily keep track of how the production process is going via their website. And then, within a week or so of ordering, they arrive. Overall, I was super impressed by PCBWay's customer service and quality of their product. Neither of the circuit boards had any problems. So thank you, PCBWay, for sending me these circuit boards free of charge. And now, it's time to build them. It's soldering time. MUSIC PLAYS The last thing we need is a brain to control it all. And I don't fancy putting chips in mine just yet. But this is an ESP. It's a small microcontroller that should work just fine for our purposes. Which means it's time for nerd stuff. And no, I won't bore you with all the code as much as I know you want to hear all about it. So let's see what it can do. MUSIC PLAYS And I also added another neat little feature to the bottom of the PCB circuit boards. After scoring these little tabs on the bottom and very carefully breaking them off... MUSIC PLAYS Then, after a quick sand and some soldering, you're left with two joining PCBs that connect multiple digits together and a breakout board that goes in the back of each digit. Now all I need is some more digits. Lucky for me, I can just go back... MUSIC STOPS And grab one from earlier. Although, in all seriousness, these digits took ages to make. But instead of sitting through months of work, I've put it all in an 80-second build montage. MUSIC PLAYS MUSIC STOPS MUSIC PLAYS And after all that, they don't work. These digits are supposed to display separate numbers, but right now they're just copying each other. So it was back to the wiring diagram. And then suddenly, it hit me. It was right there. The electricity was backtracking through a bunch of places it shouldn't be. So all I needed was a couple more diamonds. Then, after plugging in all the rest of the digits, it was time for a final test. MUSIC STOPS Yes! Finally! And it worked flawlessly. The last neat trick of this project is because we're using ESP8266, we were able to host our own website, allowing us to configure our digits and display using a variety of modes that I've programmed. This includes dice, counters, clocks, and countdowns. I won't go into too much depth of what this counter can do, but if you're interested in making your own or seeing these modes in full depth, then feel free to check out the Instructables linked in the description below. But, let's say you want to create a clock so you can keep track of time in your favourite place, such as Samoa. All you have to do is configure it on the website and then add one of these colon pieces between two digits. And then, you have a clock that keeps track of time. And, so after all this hard work, it's time to just sit back and listen to the clicks. This counter is incredibly satisfying. It makes such a lovely click noise and is everything I could have hoped for. I'm super happy with how this project turned out. And again, if you want to build your own, you can find all the files for free in the description below. If you're still here, thank you so much for watching. Subscribe, so you don't miss out on the next one.

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Let's Build a Mechanical 7-Segment Display (video, 14m)

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