Defeating Bacteria In Hot Water Systems With A Heat Exchanger

August 31, 2026 by Zoe Skyforest 39 Comments

The average hot water is a relatively simple appliance to understand. It uses gas or electricity to dump energy into water in the form of heat, keeping it at a pleasant temperature for uses like bathing and cleaning. Basic mechanisms are in place to ensure the water stays at a relatively constant temperature, neither too hot where it could cause burns, nor too cold such that it wouldn’t be fit for purpose.

One of the problems, though, is that sometimes storing water at the desired temperature can create the perfect breeding ground for bacteria. However, a neat little trick developed by NIST could solve that problem rather elegantly.

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USB-C Adapted For Legacy Sprinkler Systems

August 31, 2026 by Bryan Cockfield 31 Comments

In the modern world USB has become a truly universal connector, with its inclusion on almost every major piece of consumer electronics. It has even expanded well beyond things that we’d think of as consumer electronics, like the solenoids on automatic sprinkler systems.

This project comes to us from [Ray Wang] at opensprinkler.org who has been working on various ways of controlling the old sprinkler standards, which generally rely on a 24 VAC power supply to drive solenoids. This tests uses the power available from USB-PD and closely examines four methods of energizing the solenoids: unipolar PWM, dual voltage, synthesizing an AC wave from a DC supply, and producing a bipolar square wave. The bipolar square wave had some interesting results, being able to get pretty close to the behavior of a true sine wave while minimizing the dedrmand on power electronics.

For those working on old sprinkler systems, or many other antiquated systems that still rely on 24 VAC, this project shows that USB can deliver a surprising amount of power in unique ways, and the fact that it’s near-ubiquitous and affordable makes it that much easier to adapt into situations it was never really designed for.

These old sprinkler systems have other ways of working on modern systems as well, like this one which replaces the AC source for a DC one, but with a few caveats.

Dissecting A Lethal Universal Travel Adapter

August 30, 2026 by Maya Posch 49 Comments

The world’s refusal to standardize on a single type of mains power outlet has led to a vibrant market of so-called travel adapters, all of which try to outdo each other in convenience and universality. This comes at the cost of complexity, something which ultimately reflects in the price. The cheapo $9.26 universal travel adapter that [Brainiac 75] got off an online retailer’s site is thereby a good example of how safety suffers if the overarching goal is to ‘make it cheap’.

The first exciting discovery is that when you plug any of its three sets of connectors into an outlet, the others become live at the same voltage. This would suggest that they’re just wired together, a fact soon confirmed with a quick resistance check between the respective prongs. Though to the adapter’s credit, the prongs are not live when fully retracted into the enclosure. Yet as demonstrated in the video, the retracting of prongs is not enforced, so mistakes here are possible.

The adapter also has two USB ports that claim to provide 5 V at 2.1 A, with as it turns out no hard cut-off. This is probably the best part of the adapter despite not featuring any advanced charging features. After opening the adapter, you can see that the sliding mains prongs connect to a central bus bar when either unfolded or extended, which is definitely straightforward, but doesn’t enforce that only one type of prongs can be used at any given time.

To make it safer, [Brainiac75] removed the less useful US and UK plugs, taping over the empty holes. It’s now just a USB charger with a universal mains port to plug random non-EU plugs into, which is probably relatively safe and a better idea than really using it as a travel adapter.

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Woodstove Assistant Keeps The Heat On Safely

August 30, 2026 by Bryan Cockfield 3 Comments

Those who have never lived in a cold climate might romanticize winters around a fire, keeping warm under blankets while snow gently falls outside. While it certainly can be a cozy experience, using a woodstove comes with a number of pitfalls, and when operated improperly can even cause house-destroying chimney fires. Modern stoves operated properly with properly dried wood make this possibility extremely remote, but it’s still worth keeping an eye on. Reddit user [nas886] built a system called Oru which takes a lot of the guesswork out using one of these pieces of heating equipment.

The real danger of a woodstove isn’t necessarily running the fire too hot, although that can be a problem, but running it too cold. Without full combustion of the wood, flammable creosote builds up on the inside of the chimney which eventually can combust. This system uses a probe placed in the stovepipe to monitor the temperature of the exhaust gasses. If it’s too low an ESP32 notifies [nas886] remotely with with a status LED inside a seperate custom-built walnut enclosure so that more wood can quickly be added or airflow increased to bring up the temperature, and in the case that the fire gets too hot the LED changes to a different color and the air can be closed off a bit.

Woodstoves themselves have quite a bit of variability in the size wood they can burn, the amount they can hold at once, their efficiency, and their thermal mass, so this could find utility for anyone from those with tiny stoves that have to be fed constantly to those trying to get all-night burns in massive units, all without having to constantly sit by the fire and monitor it. [nas886] found initial success selling a few of these custom units and plans to put it into further production as well, but the general idea is not too difficult to replicate for most of us here either.

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Hacking A Cat Litter Box

August 21, 2026 by Zoe Skyforest 19 Comments

[Joseph DiGiovanni] is the owner of a Litter Robot 4. It’s a convenient mechanized litter box for cats that can clean itself to reduce unwelcome odors inside the home. He wanted to run automations based on the operation of the litter box, but was not eager to use the manufacturer’s cloud service to do it. Instead, he set about reverse engineering the device for his own ends.

Since the Litter Robot 4 relies on an ESP32 microcontroller for external connectivity, it was entirely possible for [Joseph] to whip up a custom firmware for the device instead. He started with ESPHome as a base, which is a popular firmware used for building smarthome devices based on Espressif hardware. The architecture of the Litter Robot 4 helped in this regard. It uses a PIC microcontroller to handle the low level hardware control, while the ESP32 is responsible for connecting to the cloud over WiFi. This allowed [Joseph] to mess with the connectivity features and get the device hooked up to Home Assistant without compromising the basic mechancial functionality of the device or any of the safety features.

All [Joseph] had to do was figure out how the original hardware’s ESP32 talked to the PIC and emulate that in his own firmware, which was achieved with some snooping and data capture and processing with an LLM. This was used as a basis to whip up an ESPHome firmware that could integrate the hardware neatly with Home Assistant.

Files are on Codeberg for those eager to tinker. It’s not the first time we’ve looked at cat litter management, and it won’t be the last. Video after the break.

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Smarting Up A Doorbell With Zigbee

August 19, 2026 by Zoe Skyforest 12 Comments

Once upon a time a doorbell was little more than a button, a transformer, and a bell tucked somewhere around the house. These days, they get a little bit fancier. [Philipp Schweizer] has recently been exploring how to turn existing dumb doorbells into smarter ones.

The build is based around a wired doorbell setup, in particular, a Vistadoor ADV-100. [Philipp] was able to find a simple place to tap in to a signal that went to 5 V when the doorbell was rung. He wanted to hook this into his smart home system as easily as possible. Thus, he grabbed a rather unique part—the ESP32-H2. This is notable in the ESP32 family for having no WiFi connectivity. What it does have, however, is an 802.15.4 radio good for Thread and Zigbee communications.

[Phillip] explains that hooking the ESP32-H2 up to fire a notification to Home Assistant every time the doorbell goes off is easy—and it doesn’t mess with the standard doorbell’s chiming behavior one bit. He also explains how to set up neat automations, such as having a separate smart camera capture an image when the door bell is fired.

If you’re looking to integrate an existing doorbell into your Home Assistant setup, this project could be just what you need. We’ve featured some other neat doorbell builds too, like this touchless design from the dark days of the coronavirus pandemic.

Building Custom Backyard Solar Lights

August 19, 2026 by Zoe Skyforest 20 Comments

In this modern age, if you want a truly swish garden that makes your friends sad when they visit, you need good lighting. [technocraftStudio] has been working on just such a project, creating custom wedge lights to illuminate garden beds in style.

You might look at the plastic housings involved and assume that they’re 3D printed, like the vast majority of such projects we cover these days. Instead, the enclosures are crafted out of PVC plastic, harvested by flattening sections of pipe with a heat gun. It has the benefit of being highly weather resistant, and cheap to boot. The lights themselves are small LED panels mounted on aluminium plate as a heatsink, and fitted with an acrylic diffuser to spread the light out more evenly. Power for the lights comes from an 18650 lithium-ion cell, charged by a pair of solar panels hooked up to an MPPT charge controller. A TP223 capacitive touch module is also included in the design to allow the lights to be turned on with just the touch of a finger.

The result is a surprisingly stylish bit of garden furniture which provides warm, even light and, ideally, needs a minimum of maintenance and attention since the sun provides the power. We’ve featured some other great solar lamps before, too, like this lovely Pokemon-themed build. If you’re building your own solar projects at home, or doing weird things with PVC, we’d probably love to hear about it on the tipsline!