Two types of polymer clay hand warmers with a digital temperature controller.

Adjustable Electric Hand Warmers

August 30, 2024 by Kristina Panos 6 Comments

It may be the last gasp of summer here in the Northern Hemisphere, but it’s always cold somewhere, whether it’s outdoors or inside. If you suffer from cold, stiff hands, you know how difficult it can be to work comfortably on a computer all day. Somehow, all that typing and mousing does little to warm things up. What you need are hand warmers, obviously, and they might as well be smart and made to fit your hands.

Fifteen-year-old [Printerforge] created these bad boys in an effort to learn how to code LCDs and control heat like Magneto controls ferrous metals. Thanks to digital control, they can heat up to specific temperatures, and they happen to run for a long time.

Power-wise, these warmers use a 18650 cell and a TP4056 charging module. Everything is controlled by an Arduino Nano, which reads from both a thermistor and a potentiometer to control the output.

[Printerforge] really thought this project through, as you’ll see in the Instructable. There’s everything from a table of design requirements to quick but thorough explanations of nichrome wire and basic electronic theory.

And then there’s the material consideration. [Printerforge] decided that polymer clay offers the best balance of heat conductivity and durability. They ended up with two styles — flat, and joystick grip. The best part is, everything can fit in a generous pocket.

Clay is good for a lot of things, like making the perfect custom mouse.

Power Resistance Isn’t Futile

May 14, 2024 by Al Williams 17 Comments

As [Electronoobs] points out, everything has resistance. So, how hard can it be to make a high-power resistor? In the video below, he examines a commercial power resistor and how to make your own using nichrome wire.

Sure, in theory, you can use a long piece of wire, but normally, you want to minimize the amount of space occupied. This leads to winding the wire around some substrate. If you just wind the wire, though, you get an inductor. This can cause nasty voltage spikes when there is a change in current through the resistor. You can get “noninductive” wire wound resistors that use either two opposing windings or alternate the turn direction on each turn. This causes the magnetic fields to tend to cancel out, reducing the overall inductance.

Nichrome wire has more resistance per millimeter and can dissipate more power. Modern digital meters can measure the resistance of a wire if you account for the test leads. To make a substrate, [Electronoobs] got creative since he anticipated generating a lot of heat. The final product even uses water cooling.

Why do you want a big resistor? Maybe you need a dummy load, or you want to drain some batteries. If you want to recycle nichrome wire, it is much more common than you might expect.

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Fixing An Expensive Smart Toaster Is Worth The Time

April 7, 2024 by Al Williams 49 Comments

There was a time when the simplest and cheapest kitchen appliance you could think of was a toaster. Some nichrome wire, a spring, and a mechanical thermostat were all you needed. Those days are gone and today’s toasters are full of special features, network connections, and fancy cases.

Take [boilerbot]’s Breville die-cast smart toaster. The four-slice model is upwards of $200. As Star Trek’s [Mr. Scott] said, “The more they overthink the plumbing, the easier it is to stop up the drain.” That seems to be the case here. The toaster failed and while [boilerbot] did fix it, he got lucky. He mentions that if the damage had been lower in the toaster, getting to it would have been nearly impossible.

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Foam Cutter Moves Like A Hot Knife Through Butter

July 28, 2022 by Kristina Panos 13 Comments

Make enough attempts to cut foam using whatever you’ve got — utility knife, hacksaw, serrated plastic knife — and you’ll wish hard for something that cuts cleaner, faster, and better. While there are all sorts of ways to build a hot wire foam cutter, this design from [jasonwinfieldnz] is both interesting and imitable.

If you don’t already know it, nichrome wire is nifty stuff that’s readily available in thrift store hair dryers and toasters. It stretches as it heats up, and shrinks as it cools back down.

The interesting part of this build is that instead of using a spring to keep tension on the nichrome wire, [jasonwinfieldnz] designed and 3D-printed a bow out of PLA that does the job elegantly. While [jason] was initially concerned that the bow might possibly melt, he found in practice that although the bow does get warm to the touch, it’s nowhere near hot enough to even warp.

One nice touch is the simple fence that rides along two slots and secures with wingnuts. We also like that [jason] made this foam cutter largely from scrap material, and rather than buy a spool of nichrome, he opted for a skinny heating element and pillaging the wire.

If you’re a nichrome noob, know that it doesn’t take much juice to do the job. Even though a computer power supply is what [jason] had lying around, it’s complete overkill, so you would definitely want to limit the current. Check out the build video after the break.

Still not portable enough for you? All you really need is a 18650, some nichrome, and a few bits and bobs to hold it all together.

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Hot Wire Foam Cutter Does Circles, Too

December 2, 2020 by Kristina Panos 3 Comments

Foam is all kinds of useful, but trying to cut it with scissors or a serrated plastic knife is usually an exercise in futility. What you really need is a hot wire for nice clean cuts. [Elite Worm] built a hot wire foam cutter that can cut any type of foam with ease, be it Styrofoam or grey craft foam.

There are a ton of ways to heat up a taut piece of nichrome wire, but few of them are as good looking as this one. [Elite Worm] designed and printed a table with an adjustable fence so it can be used like a table saw. There is also a circle-cutting jig that looks really handy.

This design uses a 12 V power regulator to heat up a piece of tension-adjustable nichrome wire for buttery smooth cuts. This thing looks fantastic all the way down to the cable management scheme. All the files are available on Thingiverse if you want to build one for yourself, but you’ll need to use something other than PLA.

This wire cutter is pretty versatile, but you could go even smaller with a handheld version, or build a larger, CNC-based machine.

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Hot Wire Ribbon Cutter Ceremoniously Heats Up Productivity

March 16, 2020 by Kristina Panos 8 Comments

Anyone who’s ever cut ribbon, grosgrain or otherwise, may be dismayed by the frayed edge. There are methods of avoiding this, like cutting the ribbon diagonally, or double-diagonally into a forked point, or cutting it straight across and cauterizing the threads with a lighter. But if you have a thirteen dozen baker’s dozens’ worth of goodies to festoon, ain’t nobody got time for that.

[IgorM92] made this hot wire ribbon cutter for his wife, who has a yummy-looking baking business. It combines the cutting and the heat-sealing into a single step by using the heating element from an old soldering iron. If you don’t have one of those, you could just as easily use the nichrome wire from an old hair dryer, a toaster, or wire-wound resistor.

Since the idea is essentially shorting a power source to heat up a wire, it should be done safely. [IgorM92] used a phone charger to condition mains power down to 5 V. There isn’t much else to the circuit, just a rocker switch, a power-indicating LED, and its resistor, but this simple project will no doubt save a lot of time and labor. Burn past the break to watch it ramp up production.

Nichrome wire is good for cutting foam, too. Here’s a bare-bones version that can be made in minutes.

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Arduino-Powered Rocket Test Stand

December 14, 2018 by Tom Nardi 10 Comments

If you’re into amateur rocketry, you pretty quickly outgrow the dinky little Estes motors that they sell in the toy stores. Many hobbyists move on to building their own homebrew solid rocket motors and experimenting with propellant mixtures, but it’s difficult to know if you’re on the right track unless you have a way to quantify the thrust you’re getting. [ElementalMaker] decided he’d finally hit the point where he needed to put together a low-cost test stand for his motors, and luckily for us decided to document the process and the results.

The heart of the stand is a common load cell (the sort of thing you’d find in a digital scale) coupled with a HX711 amplifier board mounted between two plates, with a small section of vertical PVC pipe attached to the topmost plate to serve as a motor mount. This configuration is capable of measuring up to 10 kilograms with an 80Hz sample rate, which is critically important as these type of rocket motors only burn for a few seconds to begin with. The sensor produces hundreds of data points during the short duration of the burn, which is perfect for graphing the motor’s thrust curve over time.

Given such a small window in which to make measurements, [ElementalMaker] didn’t want to leave anything to chance. So rather than manually igniting the motor and triggering the data collection, the stand’s onboard Arduino does both automatically. Pressing the red button on the stand starts a countdown procedure complete with flashing LED, after which a relay is used to energize a nichrome wire “electronic match” stuck inside the motor.

In the video after the break you can see that [ElementalMaker] initially had some trouble getting the Arduino to fire off the igniter, and eventually tracked the issue down to an overabundance of current that was blowing the nichrome wire too fast. Swapping out the big lead acid battery he was originally using with a simple 9V battery solved the problem, and afterwards his first test burns on the stand were complete successes.

If model rockets are your kind of thing, we’ve got plenty of content here to keep you busy. In the past we’ve covered building your own solid rocket motors as well as the electronic igniters to fire them off, and even a wireless test stand that lets you get a bit farther from the action at T-0.

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