A Tiny Tuner For The Low Power Ham

May 18, 2024 by Jenny List 10 Comments

Something that all radio amateurs encounter sooner or later is the subject of impedance matching. If you’d like to make sure all that power is transferred from your transmitter into the antenna and not reflected back into your power amplifier, there’s a need for the impedance of the one to match that of the other. Most antennas aren’t quite the desired 50 ohms impedance, so part of the standard equipment becomes an antenna tuner — an impedance matching network. For high-power hams these are big boxes full of chunky variable capacitors and big air cored inductors, but that doesn’t exclude the low-power ham from the impedance matching party. [Barbaros Aşuroğlu WB2CBA] has designed the perfect device for them: the credit card ATU.

The circuit of an antenna tuner is simple enough, two capacitors and an inductor in a so-called Pi-network because of its superficial resemblance to the Greek letter Pi. The idea is to vary the capacitances and inductance to find the best match, and on this tiny model it’s done through a set of miniature rotary switches. There are a set of slide switches to vary the configuration or switch in a load, and there’s even a simple matching indicator circuit.

We like this project, in that it elegantly provides an extremely useful piece of equipment, all integrated into a tiny footprint. It’s certainly not the first ATU we’ve brought you.

Thanks [ftg] for the tip!

An Ultra Low Power Dash Cam

April 3, 2023 by Matthew Carlson 19 Comments

Dash cameras are handy as they provide a video recording of interactions on the road. However, their utility comes from the fact that they are always recording while driving. This always-on means power draw. [Kuzysk] took it upon himself to cut that power draw by a factor of almost 70x.

He found his existing dash cam from MiVue consumed 3.5mA in idle which works out to be a whole amp-hour every 12 days. The custom version takes just 50uA which means it will draw an amp-hour in two years. The brains of the chip are formed by an ATmega328 and an LM2596M, which is a simple step-down regulator. Interestingly, [Kuzysk] purchased clones and original chips and found that the cheaper clones had a lower switching frequency but a much lower power draw. Programming an Arduino bootloader onto the board is fairly straightforward and [Kuzysk] kindly provides his code. It can detect the ACC voltage that’s on when the engine is on and is powered by a permanent 12v connection to the battery.

Overall it’s a straightforward hack that goes through rolling your own Arduino, optimizing for low power, and putting it all together into a polished project. Perhaps for the next version, he can use the ATmega to control a cheaper camera and make it smart.

Thanks to [Microchip makes] and [Abe] for the tip!

A solar-powered device with a small LCD screen

Low Power Challenge: LCD Solar Creatures Live On Sunlight, Sleep At Night

March 13, 2023 by Robin Kearey 8 Comments

With all those e-paper based projects doing the rounds these days, including in our Low Power Challenge, you’d almost forget that monochrome LCDs were the original ultra-low-power display. Without them, we wouldn’t have had watches, calculators and handheld games operating off button cell batteries or tiny solar panels back in the ’80s and ’90s. [Gabor] decided to build a set of gadgets with a 1990s LCD aesthetic, called LCD Solar Creatures. These cute little beasts live on nothing but solar power and provide some amusing animations on a classic seven-segment LCD screen.

The Creatures’ activity depends entirely on the amount of power that’s available to them. If their supercapacitors dip below 3.3 V, their micros enter a deep sleep state and do nothing except briefly flash an LED every now and then as a sign of life. When light hits the solar panel, the supercaps are charged up and the Creatures come to life and display a few basic stats. Once the caps hit 4.1 V, they really start their day and run a few programs, including a Game of Life-style simulation and an animation of Euclidean rhythms. Continue reading “Low Power Challenge: LCD Solar Creatures Live On Sunlight, Sleep At Night” →

A yellow computer with a black keyboard and a small monochrome LCD screen

Low Power Challenge: The PotatoP Runs Lisp For Months Without Recharging

March 6, 2023 by Robin Kearey 53 Comments

A common complaint among laptop users is that while battery technology has vastly improved over the past decades, a simulltaneous shrink in form factors has meant that a typical laptop today doesn’t last much longer on a battery charge than one from the early 2000s. But it doesn’t have to be that way, as [Andreas Eriksen] demonstrates with his entry for the Low Power Challenge. The PotatoP is a portable computer that should be able to run for about two years on a single battery charge, and can be topped up through an integrated solar panel.

Granted, it doesn’t have the processing power of even the cheapest laptop you can buy today, but it’s perfectly fine for [Andreas]’s use case. He’s a Lisp hacker, and a Sparkfun RedBoard Artemis can run uLisp just fine on its 48 MHz Cortex-M4F processor. The operating environment is very basic though, even requiring [Andreas] to write his own text editor, called Typo, to give him editing luxuries like backspace functionality and a movable cursor.

The Artemis board is very power-efficient by itself – typical power consumption is less than 1 mA. [Andreas] added a simple monochrome black-and-white LCD screen capable of displaying 53 columns of text, plus an SD card reader for data storage, and designed a sleek 3D-printed case to hold everything together. When running a typical piece of code, the entire system uses around 2.5 mA, which translates to about 125 days of continuous run-time on the beefy 12000 mAh lithium battery. Add a bit of solar power, plus a more realistic eight-hour working day, and the two year runtime estimated by [Andreas] appears entirely reasonable.

This has to be one of the most power-efficient portables we’ve ever seen, and one running Lisp at that. Despite its age, Lisp keeps popping up in interesting custom computers like the Lisperati1000 cyberdeck and The Lisp Badge.

Continue reading “Low Power Challenge: The PotatoP Runs Lisp For Months Without Recharging” →

Low Power Challenge: Keep Plants Green And Clean With E-Paper Smart Tags

February 25, 2023 by Dan Maloney 7 Comments

There are plenty of reasons to devote oneself to the care of houseplants — after all, a room full of bright, glossy-leaved plants can be a joy to behold, and that’s not even one of the more tangible benefits they bring. But as any green thumb knows, there’s a fine line between a healthy, vibrant plant and one that’s soon to give up the ghost.

If your thumb tends less toward green and more toward the brown and crusty side of things, something like [Jon]’s Smart Plant system might be just the thing for you. These low-power plant tags are built around increasingly ubiquitous e-Paper displays, like the kind you might find in a retail shelf price tag system. The current version of [Jon]’s tags uses a Waveshare 2.9″ tricolor display and a PCB with capacitive probes that stick into the plant’s soil. An ESP32-S lives on the top section of the PCB, along with a 1,000 mAh LiPo pack that’s charged off USB-C. The design includes an optional solar panel for keeping the battery topped off, which may or may not help depending on the plant’s place in your personal jungle.

In addition to the soil moisture sensor, the Smart Tag has an ambient temperature and humidity sensor and a light sensor — everything to keep your plant happy. The power-hungry sensors are only powered on when the Smart Tag pops out of deep sleep; this gives and estimated five to six weeks runtime between charges, without solar charging of course. The e-Paper display shows custom graphics of the plant’s current environmental state, and the same data is also available via Home Assistant thanks to the ESPHome firmware.

These are nice-looking plant tags that can really pull a lot of weight in keeping plants healthy. Check out the other offerings in our Low Power Challenge Contest, and maybe get an entry together yourself.

A clock with an e-paper display in a 3D-printed case

Low Power Challenge: E-Paper Shelf Label Becomes Ultra-Frugal Clock

February 24, 2023 by Robin Kearey 12 Comments

Over the past two decades, e-paper has evolved from an exotic and expensive display technology to something cheap enough to be used for supermarket price tags. While such electronic shelf labels are now easy to find, actually re-using them is often tricky due to a lack of documentation. Luckily, [Aaron Christophel] has managed to reverse engineer many types of shelf labels, and he’s demonstrated the results by turning one into an ultra-low-power clock called Triink. It’s based on a 128×296 pixel e-ink display paired with an nRF52832 BlueTooth Low-Energy SoC and uses just 65 micro-amperes on average: low enough to keep it running for more than a year on a single battery charge.

A PCB for an e-ink clock — Power on the left, e-ink on the right: the custom PCB is clever and compact, too

The clock is housed in an enclosure that’s simple but effective: a 3D-printed triangular prism with a slot for the screen and space for the 18650 lithium battery. One side can be opened to access the internal components, although that’s really only needed to charge the battery. You can see how cleverly everything snaps together in the video embedded below. Continue reading “Low Power Challenge: E-Paper Shelf Label Becomes Ultra-Frugal Clock” →

Low Power Challenge: Weather Station Runs For Months Thanks To E-Ink Display

February 20, 2023 by Robin Kearey 1 Comment

Having a device in your living room that shows weather information is convenient, and building one of those is a great project if you enjoy tinkering with microcontrollers and environmental sensors. It’s also a great way to learn about low-power design, as [x-labz] demonstrated with their e-ink weather station which works for no less than 60 days on a single battery charge. It has a clear display that shows the local temperature and humidity, as well as the weather forecast for the day.

The display is a 4.2″ e-paper module with a resolution of 400 x 300 pixels. It uses just 26 mW of power for a few seconds while it updates its image, and basically zero watts when showing a static picture. It’s driven by a tiny ESP32C3 processor board, which downloads the weather forecast from weatherapi.com every two hours. The indoor climate is measured by an SHT-21 temperature and humidity sensor mounted behind the display, while the outdoor data is gathered by a WiFi-connected sensor installed on [x-labz]’s balcony.

The key to achieving low power usage here is to keep the ESP32 in sleep mode as much as possible. The CPU briefly wakes up once every five minutes to read out the indoor sensor and once every fifteen minutes to gather data from outside, using the relatively power-hungry WiFi module.

To further reduce power consumption, the CPU core is driven at the lowest possible clock speed at all times: 10 MHz when reading the indoor sensor, and 80 MHz when using the WiFi connection. All of this helps ensure that just one 600 mAh lithium battery can keep everything running for those 60 days.

E-ink displays are perfect for text and simple graphics that don’t change too often, which is why they’re very popular in weather stations. With a bit of tweaking though, LCDs can also be optimized for low power.