Rotary encoders are critical to many applications, even at the hobbyist level. While considering his own rotary encoding needs for upcoming projects, it occurred to [Jan Mrázek] to try making his own DIY capacitive rotary encoder. If successful, such an encoder could be cheap and very fast; it could also in part be made directly on a PCB.
The encoder design [Jan] settled on was to make a simple adjustable plate capacitor using PCB elements with transparent tape as the dielectric material. This was used as the timing element for a 555 timer in astable mode. A 555 in this configuration therefore generates a square wave that changes in proportion to how much the plates in the simple capacitor overlap. Turn the plate, and the square wave’s period changes in response. Response time would be fast, and a 555 and some PCB space is certainly cheap materials-wise.
The first prototype gave positive results but had a lot of problems, including noise and possibly a sensitivity to temperature and humidity. The second attempt refined the design and had much better results, with an ESP32 reliably reading 140 discrete positions at a rate of 100 kHz. It seems that there is a tradeoff between resolution and speed; lowering the rate allows more positions to be reliably detected. There are still issues, but ultimately [Jan] feels that high-speed capacitive encoders requiring little more than some PCB real estate and some 555s are probably feasible.
Yes, it has its limits, but every new technology does, especially totally home-brew builds like this. The aptly named [NSA_listbot] has been putting a lot of work into his railgun, and this is but the most recent product of an iterative design cycle.
The principle is similar to other railguns we’ve featured before, which accelerate projectiles using rapidly pulsed electromagnets. The features list in the video below reads like a spec for a top-secret military project: field-augmented circular bore, 4.5kJ capacitor bank, and a custom Arduino Nano that’s hardened against the huge electromagnetic pulse (EMP) generated by the coils. But the interesting bits are in the mechanical design, which had to depart from standard firearms designs to handle the caseless 6 mm projectiles. The resulting receiver and magazines are entirely 3D printed. Although it packs a wallop, its cyclic rate of fire is painfully slow. We expect that’ll improve as battery and capacitor technology catches up, though.
We love our props here at Hackaday, and whenever we come across a piece from the Back To The Future fandom, it’s hard to resist showcasing it. In this case, [Xyster101] is showing of his build of Doc Brown’s Flux Capacitor.
[Xyster101] opted for a plywood case — much more economical than the $125 it would have cost him for a proper electrical box. Inside, there’s some clever workarounds to make this look as close as possible to the original. Acrylic rods and spheres were shaped and glued together to replicate the trinity of glass tubes, 3/4″ plywood cut by a hole saw mimicked the solenoids, steel rods were sanded down for the trio of points in the centre of the device and the spark plug wires and banana connectors aren’t functional, but complete the look. Including paint, soldering and copious use of hot glue to hold everything in place, the build phase took about thirty hours.
The LEDs have multiple modes, controlled by DIP switches hidden under a pipe on the side of the box. There’s also motion sensor on the bottom of the case that triggers the LEDs to flicker when you walk by. And, if you want to take your time-travel to-go, there’s a nine volt plug to let you show it off wherever — or whenever — you’re traveling to. Check out the build video after the break.
Linear voltage regulators are pretty easy to throw into a project if something in it needs a specific voltage that’s lower than the supply. If it needs a higher voltage, it’s almost just as easy to grab a boost converter of some sort to satisfy the power requirements. But if you’re on a mission to save some money for a large production run, or you just like the challenge of building something as simply as possible, there are ways of getting voltages greater than the supply voltage without using anything as non-minimalistic as a boost converter. [Josh] shows us exactly how this can be done using a circuit known as a charge pump to drive a blue LED.
One of the cool things about AVR microcontrollers is that they can run easily on a coin cell battery and source enough current to drive LEDs directly from the output pins. Obviously enough, if the LED voltage is greater than the voltage of the power supply, this won’t work. That is, unless you have a spare diode and capacitor around to build a charge pump.
The negative charge pump works by charging up a capacitor that is connected to an AVR pin, with the other side between the LED and a garden-variety diode to ground. That results in a roughly (VCC – 0.7) volt difference across the capacitor’s plates. When the AVR pin goes low, the other side of the capacitor goes negative by this same amount, and this makes the voltage across the LED high enough to light up. Not only is this simpler than a boost converter, but it doesn’t need any bulky inductors to work properly.
[PhysicsGirl] posts videos that would be good to use in a classroom or homeschool environment. She recently showed a 200KV capacitor made from a cake pan, a bowl, and some other common items (see video, below).
One of the most interesting things about the project was how they charged the capacitor. A PVC pipe and some common hardware made a wand that they’d charge by rubbing a foam sleeve up and down against the dome formed by a metal bowl. We might have used a cat, but there’s probably some law against that.
To discharge, they used the end of the wand and were able to get a 10 cm spark. Based on the dielectric constant for air, they estimated that equated to a 200KV charge. They also discharged it through someone’s finger, which didn’t seem like a great idea.
We’ve talked about [PhysicsGirl’s] videos before. Granted, a lot of this won’t help the experienced hacker, but if you work with kids, they are a great way to make physics interesting and approachable. We wish she’d spent more time on the actual construction (you’ll need to slow it down to see all the details), though. If you really want a capacitor for your high voltage mad science, you might find these more practical. We’ve seen many homemade capacitors for high voltage.
What do you do when you find a small horde of supercapacitors? The correct answer is a spectrum of dangerous devices ranging from gauss guns to quarter shrinkers. [Rinoa] had a less destructive idea: she’s replaced the battery in a laptop with a bank of supercapacitors.
The supercaps in question are 2.7 Volt, 500 Farad caps arranged in banks six for a total of about 3 watt-hours in each bank. The laptop used for this experiment is an IBM Thinkpad from around 1998. The stock battery in this laptop is sufficiently less advanced than today’s laptop batteries. Instead of using a microcontroller and SMBus in the battery, the only connections between the battery and laptop are power, ground, and connections for a thermocouple. This is standard for laptops of the mid-90s, and common in low-end laptops of the early 2000s. It also makes hacking these batteries very easy as there’s no associated microprocessors to futz around with.
With all the capacitor banks charged, the laptop works. It should – there isn’t a lot of intelligence in this battery. With one bank of six supercaps, [Rinoa] is getting a few minutes of power on her laptop. With a stack of supercaps that take up about the same volume as this already think Thickpad, [Rinoa] can play a few turns of her favorite late-90s turn-based strategy game. It’s not much, but it does work.
Some of the most enjoyable projects tend to have the terrible drawback of also having the most potential to cause bodily harm, like getting zapped by the capacitor when digging into a disposable camera. But often — if you’re careful — this curiosity pays off and you wind up learning how to make something cool like this coil gun from a camera flash’s capacitor. This handheld launches a small nail, and is packed in a handheld form factor with a light switch trigger.
[LabRatMatt] dispels any illusions of potential harm upfront and then repeatedly urges caution throughout his detailed guide. He breaks down the physics at work while maintaining a lighthearted tone. This coil gun uses a capacitor and charging circuit ripped from a disposable camera — [LabRatMatt] decided to double up with another capacitor that he had on hand from a previous project. The coil was repurposed from an old doorbell, but make sure to use a few hundred windings if you make your own coil. A light switch ended up being suitable for a trigger since it is able to handle the voltage spikes.
When assembled, it almost looks like something you’d expect to see in a post-apocalyptic wasteland, but it works!