USB-C Adapted For Legacy Sprinkler Systems

August 31, 2026 by Bryan Cockfield 47 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.

Leaky Player Piano Gets MIDI Upgrade In YouTube Restomod

June 17, 2026 by Tyler August 5 Comments

The word “restomod” is a bit nebulous, but it’s normally used in the automotive world to describe taking an old car and making it better-than-new with all the technological improvements the original builders would have used, had they been available. We think the word applies to [Alnwlsn]’s MIDI-actuated player piano, because what are those punched rolls of paper, but the MIDI of the 19th century?

Unlike a lot of automotive restomods though, this one is mostly reversible. He did drill few holes and slots in the original wood, but nowhere that it would alter the integrity or original operation of the player piano mechanism. The MIDI-controlled solenoids just poke the same key paddles from below that the pneumatic mechanism used. From the listener or operator’s perspective, unless the doors that reveal the music scroll or lack thereof are open, the piano behaves exactly the same. Except now it has access to the whole wide array of tracks that exist in MIDI form, rather than a paltry selection of hard-to-find piano rolls.

Each of the relays is driven by a MOSFET via shift registers to get 88 outputs out of the single Pi Pico in charge, with a level shifter involved to get the RP2040 speaking 5 V logic. If you’re wondering how that gets volume control, no, the piano isn’t smacking keys at full volume all the time. He’s using the RP2040’s powerful PIO to create a sort of PWM signal to soften the solenoid blows when needed. To save his power supply, he’s also got it set up to stagger the pulses, so multiple relays aren’t pulsed at the same time when the MIDI file calls for chords.

There was actually more overlap between player pianos and MIDI than you might think, given this presentation of an Apple ][ being used to create the piano rolls.

Continue reading “Leaky Player Piano Gets MIDI Upgrade In YouTube Restomod” →

2026 Green Powered Challenge: Supercapacitor Enables High-Power IoT

April 28, 2026 by Bryan Cockfield 3 Comments

With all the battery technologies and modern low-current sleep modes in most microcontrollers, running a sensor and microcontroller combo off-grid and far away from any infrastructure is usually not too difficult a task. Often these sorts of systems can go years without maintenance or interaction. But for something that still has to be off-grid but needs to do some amount of work every now and then like actuating a solenoid or quickly turning a servo, these battery-based systems can quickly run out of juice. To solve that problem, [Nelectra] has come up with this high-power capacitor-based IoT system.

Although supercapacitors don’t tend to have the energy density of batteries, they’re perfectly capable of powering short tasks in off-grid situations like this. They’re also typically able to tolerate lower voltages, extreme temperatures, and shock better than most batteries as well. A small solar cell on the top of this device keeps it topped up, and when running in deep sleep mode can hold a charge for up to six days. In more real-world applications supporting sensors, relays, or other actuators, [Nelectra] has found that it can hold a charge for around three days. When a quick burst of power is needed, it can deliver 1.5 A at 9 V or 500 mA at 24 V.

[Nelectra]’s stated goal for this build is to bridge low-power energy harvesting and practical field actuation, enabling maintenance-free systems such as irrigation control and remote switching without batteries, going beyond simple sensor applications while not relying on always-on power from somewhere else. Something like this would work really well in applications like this automated farm, which has already provided some unique solutions to intermittent power and microcontroller applications that need very high reliability.

Converting AC Irrigation Valves To DC Operation

February 9, 2026 by Zoe Skyforest 34 Comments

Due to historical engineering decisions made many decades ago, a great many irrigation systems rely on solenoid valves that operate on 24 volts AC. This can be inconvenient if you’re trying to integrate those valves with a modern smart home control system. [Johan] had read that there were ways to convert these valves to more convenient DC operation, and dived into the task himself.

As [Johan] found, simply wiring these valves up to DC voltage doesn’t go well. You tend to have to lower the voltage to avoid overheating, since the inductance effect used to limit the AC current doesn’t work at DC. However, even at as low as 12 volts, you might still overheat the solenoids, or you might not have enough current to activate the solenoid properly.

The workaround involves wiring up a current limiting resistor with a large capacitor in parallel. When firing 12 volts down the line to a solenoid valve, the resistor acts as a current limiter, while the parallel cap is initially a short circuit. This allows a high current initially, that slowly tails off to the limited value as the capacitor reaches full charge. This ensures the solenoid valve switches hard as required, but keeps the current level lower over the long term to avoid overheating. According to [Johan], this allows running 24V AC solenoid valves with a 12V DC supply and some simple off-the-shelf relay boards.

We’ve seen similar work before, which was applied to great effect. Sometimes doing a little hack work on your own can net you great hardware to work with. If you’ve found your own way to irrigate your garden as cheaply and effectively as possible, don’t hesitate to notify the tipsline!

DIY Pinball Machine Uses Every Skill

November 1, 2025 by Bryan Cockfield 6 Comments

Pinball machines have something for everyone. They’re engaging, fast-paced games available in a variety of sizes and difficulties, and legend has it that they can be played even while deaf and blind. Wizardry aside, pinball machines have a lot to offer those of us around here as well, as they’re a complex mix of analog and digital components, games, computers, and artistry. [Daniele Tartaglia] is showing off every one of his skills to build a tabletop pinball machine completely from the ground up.

Continue reading “DIY Pinball Machine Uses Every Skill” →

Converting A Sprinkler System To DC

August 22, 2025 by Bryan Cockfield 14 Comments

Famously, Nikola Tesla won the War of the Currents in the early days of electrification because his AC system could use transformers to minimize losses for long distance circuits. That was well before the invention of the transistor, though, and there are a lot of systems that still use AC now as a result of electricity’s history that we might otherwise want to run on DC in our modern world. Sprinkler systems are one of these things, commonly using a 24V AC system, but [Vinthewrench] has done some work to convert over to a more flexible 24 VDC system instead.

The main components of these systems that are set up for AC are solenoids which activate various sets of sprinklers. But these solenoids can take DC and still work, so no major hardware changes are needed. It’s not quite as simple as changing power supplies, though. The solenoids will overheat if they’re fully powered on a DC circuit, so [Vinthewrench] did a significant amount of testing to figure out exactly how much power they need to stay engaged. Once the math was done, he uses a DRV103 to send PWM signals to the solenoids, which is set up to allow more current to pull in the solenoids and then a lower holding current once they are activated.

With a DC power supply like this, it makes it much easier to have his sprinkler system run on a solar powered system as well as use a battery backup without needing something like an inverter. And thanks to the DRV103 the conversion is not physically difficult; ensuring that the solenoids don’t overheat is the major concern here. Another great reason to convert to a DIY sprinkler controller is removing your lawn care routine from an unnecessary cloud-based service.

Wireless Doorbell Extension Features Home-Wound Coil

May 16, 2025 by John Elliot V 12 Comments

Today in the it’s-surprising-that-it-works department we have a ding dong doorbell extension from [Ajoy Raman].

What [Ajoy] wanted to do was to extend the range of his existing doorbell so that he could hear it in his workshop. His plan of attack was to buy a new wireless doorbell and then interface its transmitter with his existing doorbell. But his approach is something others might not have considered if they had have been tasked with this job, and it’s surprising to learn that it works!

What he’s done is wrap a new coil around the ding dong doorbell’s solenoid. When the solenoid activates, a small voltage is induced into the coil. This then gets run into the wireless doorbell transmitter power supply (instead of its battery) via a rectifier diode and a filter capacitor. The wireless doorbell transmitter — having also had its push-button shorted out — operates for long enough from this induced electrical pulse to transmit the signal to the receiver. To be clear: the wireless transmitter is fully powered by the pulse from the coil around the solenoid. Brilliant! Nice hack!

We weren’t sure how reliable the transmitter would be when taken out of the lab and installed in the house so we checked in with [Ajoy] to find out. It’s in production now and operating well at a distance of around 50 feet!

Of course we’ve published heaps of doorbell hacks here on Hackaday before, such as this Bluetooth Low Energy (BLE) doorbell and this light-flashing doorbell. Have you hacked your own doorbell? Let us know on the tips line!

Continue reading “Wireless Doorbell Extension Features Home-Wound Coil” →