Toothbrush Speed Controller Secrets Revealed

May 18, 2023 by Lewin Day 21 Comments

Typically, when we want to build something with a DC motor, we might grab a bunch of AAs, or a single lithium cell at the very least. Electric toothbrushes often run on more humble power sources, like a single NiMH battery. They’re designed to get useful motion out of just 1.2V, and [Marian Hryntsiv] has taken a look at what makes them tick.

The article focuses on an electric toothbrush built around the Low Voltage GreenPAK™ SLG47513 chip. It’s designed to work at voltages from just 1 to 1.65 V. To make the most of the limited power available, the toothbrush stays in sleep mode most of the time when it’s not working in oral health.

[Marian] steps through the various parts of the circuit, and also explains the unique functionality baked into the brush. Of particular interest are the timer routines that guide the user through brushing each section of the mouth in turn, before a notification that tells them that 2 minutes of brushing time has elapsed. There’s also a useful explanation of the inductive charging method used.

Electric toothbrushes may be mundane home items today, but they’re an example of a product that has largely already been optimized to the nth degree. Until laser-based plaque removal or enamel regeneration technology gets off the ground, this is as good as it gets. We can dream, though!

Tube Amplifier Uses Low Voltage, Sips Battery

April 6, 2023 by Bryan Cockfield 25 Comments

Much like vinyl records, tube amplifiers are still prized for their perceived sound qualities, even though both technologies have been largely replaced otherwise. The major drawback to designing around vacuum tubes, if you can find them at all, is often driving them with the large voltages they often require to heat them to the proper temperatures. There are a small handful of old tubes that need an impressively low voltage to work, though, and [J.G.] has put a few of them to work in this battery-powered audio tube amplifier.

The key to the build is the Russian-made 2SH27L battery tubes which are originally designed in Germany for high-frequency applications but can be made to work for audio amplification in a pinch. The power amplifier section also makes use of 2P29L tubes, which have similar characteristics as far as power draw is concerned. Normally, vacuum tubes rely on a resistive heater to eject electrons from a conductive surface, which can involve large amounts of power, but both of these types of tubes are designed to achieve this effect with only 2.2 volts provided to the heaters.

[J.G.] is powering this amplifier with a battery outputting 5V via a USB connection, and driving a fairly standard set of speakers borrowed from a computer. While there aren’t any audio files for us to hear, it certainly looks impressive. And, as it is getting harder and harder to find vacuum tubes nowadays, if you’re determined to build your own amplifier anyway take a look at this one which uses vacuum tubes built from scratch.

Breakers for the system on a DIN rail, with markings like 48V and 24V and 12V and so on on the bottom, and two hefty devices of some kind on the bottom, probably MPTT controllers, with hefty wires running from them.

Low-Voltage DC Network Build Incited By Solar Panels

November 2, 2022 by Arya Voronova 50 Comments

Nowadays, some people in Europe worry about energy prices climbing, and even if all the related problems disappear overnight, we’ll no doubt be seeing some amounts of price increase. As a hacker, you’re in a good position to evaluate the energy consuming devices at your home, and maybe even do something about them. Well, [Peter] put some solar panels on his roof, but couldn’t quite figure out a decent way to legally tie them into the public grid or at least his flat’s 220V network. Naturally, a good solution was to create an independent low-voltage DC network in parallel and put a bunch of devices on it instead!

He went with 48V, since it’s a voltage that’s high enough to be efficient, easy to get equipment like DC-DCs for, safe when it comes to legal matters concerned, and overall compatible with his solar panel setup. Since then, he’s been putting devices like laptops, chargers and lamps onto the DC rail instead of having them be plugged in, and his home infrastructure, which includes a rack full of Raspberry Pi boards, has been quite content running 24/7 from the 48V rail. There’s a backup PSU from regular AC in case of overcast weather, and in case of grid power failures, two hefty LiFePO4 accumulators will run all the 48V-connected appliances for up to two and a half days.

The setup has produced and consumed 115kWh within the first two months – a hefty contribution to a hacker’s energy independence project, and there’s enough specifics in the blog post for all your inspiration needs. This project is a reminder that low-voltage DC network projects are a decent choice on a local scale – we’ve seen quite viable proof-of-concept projects done at hackercamps, but you can just build a small DC UPS if you’re only looking to dip your feet in. Perhaps, soon we’ll figure out a wall socket for such networks, too.

A Lot Of Effort For A Pi Laptop

April 13, 2021 by Bryan Cockfield 7 Comments

Building a Raspberry Pi laptop is not that uncommon. In fact, just a few clicks from any of the major electronics suppliers will have the parts needed for such a project speeding on their way to your house in no time at all. But [joekutz] holds the uncontroversial belief that the value in these parts has somewhat diminishing returns, so he struck out to build his own Pi laptop with a €4 DVD player screen and a whole lot of circuit wizardry to make his parts bin laptop work.

The major hurdle that he needed to overcome was how to power both the display and the Pi with the two small battery banks he had on hand. Getting 5V for the Pi was easy enough, but the display requires 8V so he added one lithium ion battery in series (with its own fuse) in order to reach the required voltage. This does make charging slightly difficult but he also has a unique four-pole break-before-make switch on hand which doesn’t exactly simplify things, but it does make the project function without the risk of short-circuiting any of the batteries he used.

The project also makes use of an interesting custom circuit which provides low voltage protection for that one lonely lithium battery as well. All in all it’s a master course in using some quality circuit-building skills and electrical theory to make do with on-hand parts (and some 3D printing) rather than simply buying one’s way out of a problem. And the end result is something that’s great for anything from watching movies to playing some retro games.

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PCB Mods Silence Voltage Warnings On The Pi 4

February 12, 2021 by Tom Nardi 122 Comments

If you’ve ever pushed the needle a bit on your Raspberry Pi, there’s a good chance you’ve been visited by the dreaded lightning bolt icon. When it pops up on the corner of the screen, it’s a warning that the input voltage is dipping into the danger zone. If you see this symbol often, the usual recommendation is to get a higher capacity power supply. But experienced Pi wranglers will know that the board can still be skittish.

Sick of seeing this icon during his MAME sessions, [Majenko] decided to attack the problem directly by taking a close look at the power supply circuitry of the Pi 4. While the official schematics for everyone’s favorite single-board computer are unfortunately incomplete, he was still able to identify a few components that struck him as a bit odd. While we wouldn’t necessarily recommend you rush out and make these same modifications to your own board, the early results are certainly promising.

The first potential culprit [Majenko] found was a 10 ohm resistor on the 5 V line. He figured this part alone would have a greater impact on the system voltage than a dodgy USB cable would. The components aren’t labeled on the Pi’s PCB, but with a little poking of the multimeter he was able to track down the 0402 component and replace it with a tiny piece of wire. He powered up the Pi and ran a few games to test the fix, and while he definitely got fewer low-voltage warnings, there was still the occasional brownout.

Going back to the schematic, he noticed there was a 10 uF capacitor on the same line as the resistor. What if he bumped that up a bit? The USB specifications say that’s the maximum capacitive load for a downstream device, but he reasoned that’s really only a problem for people trying to power the Pi from their computer’s USB port.

Tacking a 470 uF electrolytic capacitor to the existing SMD part might look a little funny, but after the installation, [Majenko] reports there hasn’t been a single low-voltage warning. He wonders if the addition of the larger capacitor might make removing the resistor unnecessary, but since he doesn’t want to mess with a good thing, that determination will be left as an exercise for the reader.

It’s no secret that the Raspberry Pi 4 has been plagued with power issues since release, but a newer board revision released last year helped smooth things out a bit. While most people wouldn’t go this far just to address the occasional edge case, it’s good to know folks are out there experimenting with potential fixes and improvements.

So Where’s My Low Voltage DC Wall Socket?

December 21, 2016 by Jenny List 185 Comments

What are the evocative sounds and smells of your childhood? The sensations that you didn’t notice at the time but which take you back immediately? For me one of them is the slight smell of phenolic resin from an older piece of consumer electronics that has warmed up; it immediately has me sitting cross-legged on our living room carpet, circa 1975.

"Get ready for a life that smells of hot plastic, son!" John Atherton [CC BY-SA 2.0], via Wikimedia Commons. — “Get ready for a life that smells of hot plastic, son!” John Atherton [CC BY-SA 2.0], via Wikimedia Commons.

That phenolic smell has gone from our modern electronics, not only because modern enclosures are made from ABS and other more modern plastics, but because the electronics they contain no longer get so hot. Our LCD TV for instance nowadays uses only 50 watts, while its 1970s CRT predecessor would have used several hundred. Before the 1970s you would not find many household appliances that used less than 100 watts, but if you take stock of modern electrical appliances, few use more than that. Outside the white goods in your kitchen and any electric heaters or hair dryers you may own, your appliances today are low-powered. Even your lighting is rapidly being taken over by LEDs, which are at their heart low-voltage devices.

There are many small technological advancements that have contributed to this change over the decades. Switch-mode power supplies, LCD displays, large-scale integration, class D audio and of course the demise of the thermionic tube, to name but a few. The result is often that the appliance itself runs from a low voltage. Where once you would have had a pile of mains plugs competing for your sockets, now you will have an equivalent pile of wall-wart power supplies. Even those appliances with a mains cord will probably still contain a switch-mode power supply inside.

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Ask Hackaday: Dude, Where’s My MOSFET?

December 13, 2016 by Elliot Williams 126 Comments

(Bipolar Junction) Transistors versus MOSFETs: both have their obvious niches. FETs are great for relatively high power applications because they have such a low on-resistance, but transistors are often easier to drive from low voltage microcontrollers because all they require is a current. It’s uncanny, though, how often we find ourselves in the middle between these extremes. What we’d really love is a part that has the virtues of both.

The ask in today’s Ask Hackaday is for your favorite part that fills a particular gap: a MOSFET device that’s able to move a handful of amps of low-voltage current without losing too much to heat, that is still drivable from a 3.3 V microcontroller, with bonus points for PWM ability at a frequency above human hearing. Imagine driving a moderately robust small DC robot motor forwards with a microcontroller, all running on a LiPo — a simple application that doesn’t need a full motor driver IC, but requires a high-efficiency, moderate current, and low-voltage-logic compatible transistor. If you’ve been here and done that, what did you use?

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