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Getting To Know The TP223 Capacitive Touch Sensor

October 9, 2026 by 14 Comments

Mechanical and prone to failure, switches can seem quaint these days. Plus, everyone is used to having touch screens on their phones and other devices. So why not use touch sensors on your next project? [Tarantula3] has details on using the TP223 instead of ordinary switches.

These inexpensive modules work through plastic, glass, or wood, opening up many interesting possibilities for building a front panel. Of course, the thicker the surface above the module, the less sensitive the switch is, but that’s not always a bad thing. In particular, you may want to reduce sensitivity anyway. Thicker panels, reducing the size of the touch pad, or adding an external capacitor can reduce the sensor’s range.

You may be worried about eating up batteries with a bunch of electronic switches. But according to [Tarantula3], the modules consume less than 2 microamps at rest. You can configure the modules with our favorite scripting language: solder. There are two jumpers, initially unsoldered, and this results in four possible states. By default, the output goes high when someone is touching the sensor and stays high until they release.

However, you can solder jumper A to invert the output. Jumper B causes the switch output to toggle on each press. Of course, you can also do both jumpers, which toggles but has the opposite default state. If you get false triggers, consider adding a small capacitor to filter the power supply to the module.

These would be great “drop ins” for 3D printing to add switches to your designs. You might even be able to use these as power switches with a little work.

Ways To Empirically Identify A Magnet’s Polarity

September 27, 2026 by 13 Comments

Every magnet has a north and a south pole, but which is which? Sometimes it matters. If a product one builds features a magnetic closure or other part, the polarity of those magnets should be consistent in assembly. So how does one ensure they never glue a magnet wrong again? [Clough42] shows several ways to identify a magnet’s north and south poles using things many of us probably have ready at hand, and goes into a bit of theory while he’s at it.

Probably the easiest way is to use a known-good and clearly labeled reference magnet. Same poles repel, and opposites attract. But if that’s not available, a simple magnetic compass can help. Because opposite poles attract, a compass’s north point will be attracted toward a magnet’s south pole, and vice versa.

A Hall effect sensor, or an electromagnet — the winding and current flow determine the polarity — are other ways to measure a magnet’s poles. And here’s where [Clough42] dives into some details of how magnetic fields actually act, because it explains some seemingly strange behavior.

For example, at around 4:08 he demonstrates a Hall effect sensor board that is documented as lighting an LED when the south pole of a magnet is held to its front. It does that, but it also lights the LED when the north end of the magnet is held to the sensor’s back. That’s because the sensor isn’t actually directly sensing the magnet’s pole, it’s sensing the orientation of a magnetic field. The lesson is clear: make sure you’re measuring what you think you’re measuring. Near the end of the video he demonstrates a similar experience with a handy mobile phone app that senses magnetic fields by reading the device’s internal magnetic compass; by waving a strong magnet around, the detected polarity flips back and forth even though the magnet’s orientation isn’t changed.

So what does one do after positively identifying a magnet’s north and south poles? Label it clearly for use as a known-good reference magnet in the future is our suggestion. Watch the whole video below, then take a few minutes to dive into the nitty-gritty of what magnets actually are and how they work.

Continue reading “Ways To Empirically Identify A Magnet’s Polarity” →

The Different Ways To Look At Negative Resistance

September 8, 2026 by 22 Comments

[lcamtuf] has an in-depth look at the concept of negative resistance that goes somewhat further than one might expect. Normally, as voltage across a resistance increases so too does the current. Negative resistance is the concept of current decreasing as voltage increases. But beyond the raw concept, there are a few other ways to look at this idea.

The usual way to think about it is negative differential resistance (NDR). Not everything has a linear relationship between voltage and current, and for a device to exhibit NDR means that in certain ranges the I–V curve actually slopes downward; increasing one of voltage or current decreases the other. This kind of thing occurs in neon lamps. Once they are glowing, increasing current can result in decreasing voltage.

True negative resistance, that of a literal -100 Ω resistor, does not exist. Not in the sense of a passive component, anyway. Such a device would supply power into a circuit rather than dissipating it, and would therefore require an external power source to do so. If that’s not a deal breaker, then it’s actually fairly simple to build one. [lcamtuf] provides a design for a device that uses an op-amp to exhibit ideal constant negative resistance. Naturally it only does so within its operating range; going beyond risks letting out the magic smoke.

Is making a literal negative resistor of practical use? Perhaps only in very specialized situations. But it is worth having a basic understanding if for no other reason than it rears its head in unusual places: the strange tunnel diode comes to mind.

Casting Engine Parts From 3D Prints

August 28, 2026 by 29 Comments

After building a couple of internal combustion engines by milling billet aluminium stock and cringing at the absolute waste of material this created, [Camden Bowen] figured he’d give casting metal parts a shot. Of course, the key here is to create the molds for said casting, which is where you got a few options available.

Since DIY is really his thing, he also made his own kiln using cement and perlite, plus a propane burner. For the aluminium material to melt, he bought a stack of aluminium alloy wheels, as these are made of an alloy that’s actually suitable for casting. These were turned into ingots as a first step towards casting the engine parts, which among other things helps to purify the metal.

For the actual casting method he picked lost PLA, meaning the intended shape is 3D printed in PLA, then put into plaster before it’s melted out of the newly minted mold in an oven and subsequently burned out in the kiln. For the plaster [Camden] used regular Plaster of Paris, mixed with sand to give it suitable heat-resistant properties.

After some trial and error, as well as a lot of trouble burning out all the PLA, he got a usable mold and managed to eventually cast an engine cylinder with only a few imperfections. Considering just how convoluted it would have been to mill that part out of billet aluminium, it’s easy to see why commercial manufacturers are casting such parts as well.

Continue reading “Casting Engine Parts From 3D Prints” →

Robotic Screw And Bolt Sorter Seeks A New Challenge

August 8, 2026 by 21 Comments

As someone who disassembles and repairs hardware, [Aad] eventually ended up with a huge collection of mixed bolts and screws. This led to creating the automatic bolt and screw sorting system you see here, although in a way it is just a proof of concept. Bolts and screws happen to be a useful application for now, but the system is capable of sorting just about any small objects.

A bit of machine vision detects the size and shape of each object. Weight can also be measured.

Mixed pieces go onto a large conveyor belt, shown on the right. This feeds a few screws at a time down a chute, where they roll onto an illuminated platform.

Above the lit platform is a camera, and machine vision is used to detect the size and shape and orientation of each screw. A robotic gripper on a gantry picks the screws up one by one — separating them first if they happened to clump together — and places each in a drop-off cart. The cart drops the object into a receptacle with its brethren, making sure similar ones are grouped together. Watch it in action in the video, embedded below the page break.

It’s a great build that shows fancy components aren’t necessary for good results. Servos and steppers are controlled with an ESP32-WROOM board, and a piezo sensor detects screws falling off the conveyor. Some of you may have noticed a repurposed Ultimaker 3D printer serving as the bulk of the system, its hot end having been replaced with a gripper that can raise and lower. The overhead camera is an ESP32-CAM adapted to accept M12 lenses so it can focus on the platform.

There’s one more feature worth mentioning — the system also has the ability to measure the weight of a picked object by placing it onto a moveable inspection platform, which can optionally put it under a USB microscope for a closer look. Everything is controlled by a nearby PC, so there’s a lot of flexibility built into the system.

We suppose that once all the screws and bolts in a shop are sorted, it only makes sense to sort all the nuts. Are there other objects besides screws and bolts that would be useful to sort with a system like this? If you have any ideas, don’t keep them to yourself! [Aad] would love to hear your comments and ideas, so share them below.

Continue reading “Robotic Screw And Bolt Sorter Seeks A New Challenge” →

Junkbin, A Way To Efficiently Reuse Your Old Electronics

August 8, 2026 by 31 Comments

We all have that bin in the corner of our shops — the one with all the circuit boards or broken electronics that we are totally gonna do something with. We might rationalize that they’re worth keeping for the parts alone, but the reality is, unless you desolder and sort all the components ahead of time, most of us will never really use these spare parts to their full potential. Except it really doesn’t have to be that way. Junkbin.io is an attempt to improve on the state of that corner bin.

Though in its early years, Junkbin has a variety of the previously mentioned resources as well as many others. Currently, it is ripe to contribute, and we here at Hackaday know how important the community is to get these projects truly off the ground and to their full potential.

Created by [Steve Cap], Junkbin is a community dictionary of sorts to document and reuse electronic components found on many of the devices found around you. Do you need a single small form factor resistor of a specific resistance? That’s where Junkbin comes in to show you where you might find that specific component.

If you want a more macro-scale example of electronics recycling, make sure to check out our other featured projects such as these reused laptops! Or maybe take a look at this graveyard of defunct electronics to add to Junkbin…

A 3D Printed Cycloidal Gearbox

August 6, 2026 by 5 Comments

Stepper motors are undeniably useful, but sometimes they need a bit of gearing to help perform their task. [Gjhudson2008] has a compact gearbox for NEMA 17 or 23 steppers that is mostly 3D printed. How compact? The gearbox, named VANTIX, is exactly the height of a standard NEMA 17 axle.

However, for it to be that thin, your stepper has to have the D-bore on the shaft go all the way down. Some steppers leave a shank uncut at the base, and that won’t work for VANTIX.

The recommendation is to print in ABS with a 0.2 mm nozzle for certain parts to help improve tolerance. Most of the assembly is either press fit or installed during the printing process. Some parts of the gearbox are better to print with a larger nozzle, too.

There are some heat-set inserts and, of course, you’ll need lube to keep everything moving smoothly. There are a few top plates you can print to fit various mounting scenarios.

We have seen a number of similar designs. We’ve also looked at some e-bike-inspired drives.