Misc Hacks

4170 Articles

Blinking An LED With A Single Transistor

October 20, 2025 by 16 Comments

Let’s say you want to blink an LED. You might grab an Arduino and run the Blink sketch, or you might lace up a few components to a 555. But you needn’t go so fancy! [The Design Graveyard] explains how this same effect can be achieved with a single transistor.

The circuit in question is rather odd at first blush. The BC547 NPN transistor is hooked up between an LED and a resistor leading to a 12V DC line, with a capacitor across the emitter and collector. Meanwhile, the base is connected to… nothing! It’s just free-floating in the universe of its own accord. You might expect this circuit to do nothing at all, but if you power it up, the LED will actually start to flash.

The mechanism at play is relatively simple. The capacitor charges to 12 volts via the resistor. At this point, the transistor, which is effectively just acting as a poor diode in this case, undergoes avalanche breakdown at about 8.5 to 9 volts, and starts conducting. This causes the capacitor to discharge via the LED, until the voltage gets low enough that the transistor stops conducting once again. Then, the capacitor begins to charge back up, and the cycle begins again.

It’s a weird way to flash an LED, and it’s not really the normal way to use a transistor—you’re very much running it out of spec. Regardless, it does work for a time! We’ve looked at similar circuits before too. Video after the break.

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Classy Desk Simulates Beehive Activity

October 20, 2025 by 6 Comments

Beehives are impressive structures, an example of the epic building feats that are achievable by nature’s smaller creatures. [Full Stack Woodworking] was recently building a new work desk, and decided to make this piece of furniture a glowing tribute to the glorious engineering of the bee. (Video, embedded below.)

The piece is a conventional L-shaped desk, but with a honeycomb motif inlaid into the surface itself. [Full Stack Woodworking] started by iterating on various designs with stacked hexagons made out of laser cut plywood and Perspex, filled with epoxy. Producing enough hexagons to populate the entire desk was no mean feat, requiring a great deal of cutting, staining, and gluing—and all this before the electronics even got involved! Naturally, each cell has a custom built PCB covered in addressable LEDs, and they’re linked with smaller linear PCBs which create “paths” for bees to move between cells.

What’s cool about the display is that it’s not just running some random RGB animations. Instead, the desk has a Raspberry Pi 5 dedicated to running a beehive simulation, where algorithmic rules determine the status (and thus color) of each hexagonal cell based on the behavior of virtual bees loading the cells with honey. It creates an organic, changing display in a way that’s rather reminiscent of Conway’s Game of Life.

It was a huge build, but the final result is impressive. We’ve featured some other great custom desks over the years too. Video after the break.

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Decoding A 350 Year Old Coded Message

October 19, 2025 by 2 Comments

Usually, a story about hacking a coded message will have some computer element or, at least, a machine like an Enigma. But [Ruth Selman] recently posted a challenge asking if anyone could decrypt an English diplomatic message sent from France in 1670. Turns out, two teams managed it. Well, more accurately, one team of three people managed it, plus another lone cryptographer. If you want to try decoding it yourself, you might want to read [Ruth’s] first post and take a shot at it before reading on further here: there are spoilers below.

No computers or machines were likely used to create the message, although we imagine the codebreakers may have had some mechanized aids. Still, it takes human intuition to pull something like this off. One trick used by the text was the inclusion of letters meant to be thrown out. Because there were an odd number of Qs, and many of them were near the right margin, there was a suspicion that the Qs indicated a throw-away character and an end of line.

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A photo of the camera.

F/0.38 Camera Lens Made With Oil Immersion Microscope Objective

October 17, 2025 by 14 Comments

Over on YouTube [Applied Science] shows us how to make an f/0.38 camera lens using an oil immersion microscope objective.

The f-number of a lens indicates how well it will perform in low-light. To calculate the f-number you divide the focal length by the diameter of the aperture. A common f-number is f/1.4 which is generally considered “fast”.

We are told the fastest commercial lens ever used had f/0.7 and was used by Stanley Kubrick to shoot the film Barry Lyndon which was recorded only with candle light.

A microscope objective is a crucial lens that gathers and magnifies light to form an image. It plays a key role in determining the quality and clarity of the final magnified image produced by a microscope.

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Positive Results With Negative Resistance

October 16, 2025 by 18 Comments

Try an experiment. Next time you are in a room with someone, ask them to name everything in the room. Only certain kinds of people will say “air” or “light.” For most people, those are just givens, and you don’t think about them unless, for some reason, you don’t have them. Resistance is like that in electronics. You use it constantly, but do you ever think much about what it is? For a resistor, the value in ohms really represents the slope of the line that describes the amount of voltage you’ll see across the component when it carries a certain amount of current. For resistors, that slope is — at least in theory — constant and positive. But [Void Electronics] made a video exploring negative resistance, and it is worth watching, below.

If you haven’t seen negative resistance before, you might wonder how that is possible. Ohm’s law is just a shorthand for calculating the slope of a graph with voltage on the Y axis and current on the X axis. It works because the voltage and current are always zero at the same time, so the slope is (V-0)/(I-0), and we just shorten that to the normal Ohm’s law equation.

But not everything has a linear response to current. Some devices will have different slopes over different current regions. And sometimes that slope can be negative, meaning that an increase in current through the device will cause it to drop less voltage. Of course, this is usually just over a narrow range and, as [Void] points out, most devices don’t specify that parameter on their data sheets. In fact, some transistors won’t even work in the circuit.

The circuit in question in the video below the break is an odd one. It uses two resistors, an LED, and a transistor. But the transistor’s base is left disconnected. No 555 needed. How does it work? Watch the video and you’ll see. There’s even a curve tracer if you don’t like to see hand-drawn graphs.

We’ve looked at negative resistance more than once. There are a few exotic devices, like tunnel diodes, that are explicitly used for the negative resistance property. When the gas in a neon bulb breaks down, you get the same effect. Continue reading “Positive Results With Negative Resistance” →

A photo of the old mechanical and new digital altimeters

Ben Eater Explains How Aircraft Systems Communicate With The ARINC 429 Protocol

October 14, 2025 by 6 Comments

Over on his YouTube channel the inimitable [Ben Eater] takes a look at an electronic altimeter which replaces an old mechanical altimeter in an airplane.

The old altimeter was entirely mechanical, except for a pair of wires which can power a backlight. Both the old and new altimeters have a dial on the front for calibrating the meter. The electronic altimeter has a connector on the back for integrating with the rest of the airplane. [Ben] notes that this particular electronic altimeter is only a backup in the airplane it is installed in, it’s there for a “second opinion” or in case of emergency.

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Motors Make The Best Knobs With SimpleFOC

October 9, 2025 by 17 Comments

The worst thing about a volume knob is that, having connected it to a computer, it might be wrong: if you’ve manually altered the volume settings somewhere else, the knob’s reading won’t be correct. [I Got Distracted] has a quick tutorial on YouTube showing how to use a BLDC, a hall effect sensor, Pi Pico and the SimpleFOC library to make a knob with active haptic feedback and positioning.

We covered the SimpleFOC library a few years ago, but in case you missed it, it’s, well, a simple library for FOC on all of our favorite microcontrollers, from Arduino to ESP to Pico. FOC stands for field-oriented control, which is a particular way of providing smooth, precise control to BLDCs. (That’s a BrushLess DC motor, if the slightly-odd acronym is new to you.) [I Got Distracted] explains exactly how that works, and shows us just how simple the SimpleFOC project is to use in this video.  Why, they even produce their own motor controllers, for a fully-integrated experience. (You aren’t restricted to that hardware, but it certainly does make things easy.)

The haptic feedback and self-dialing knob make for an easy introductory project, but seeing how quick it hacks together, you can doubtless think of other possibilities. The SimpleFOC controller used in this video is limited to relatively small motors, but if you want to drive hundreds of kilowatts through open source hardware, we’ve covered that, too.  

Arguably, using a motor as a knob isn’t within the design spec, and so could almost qualify for our ongoing Component Abuse Challenge, had [I Got Distracted] thought to enter.

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