Datalogger uses ESP32 and ESP8266 Low Power Modes

[G6EJD] wanted to design a low power datalogger and decided to look at the power consumption of an ESP32 versus an ESP8266. You can see the video results below.

Of course, anytime someone does a power test, you have to wonder if there were any tricks or changes that would have made a big difference. However, the relative data is interesting (even though you could posit situations where even those results would be misleading). You should watch the videos, but the bottom line was a 3000 mAh battery provided 315 days of run time for the ESP8266 and 213 days with the ESP32.

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How Low-Power Can You Go?

[lasersaber] has a passion: low-power motors. In a bid to challenge himself and inspired by betavoltaic cells, he has 3D printed and built a small nuclear powered motor!

This photovoltaic battery uses fragile glass vials of tritium extracted from keychains and a small section of a solar panel to absorb the light, generating power. After experimenting with numerous designs, [lasersaber] went with a 3D printed pyramid that houses six coils and three magnets, encapsulated in a glass cloche and accompanied by a suitably ominous green glow.

Can you guess how much power and current are coursing through this thing? Guess again. Lower. Lower.

Under 200mV and 20nA!

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At Last, (Almost) A Cellphone With No Batteries!

If you are tired of constantly having to worry about the state of the battery in your mobile phone, then maybe help is at hand courtesy of the University of Washington. They are reporting the first-ever battery free cell phone, able to make calls by scavenging ambient power. An impressive achievement, and one about which we’d all like to know more.

On closer examination though, the story is revealed as not quite what it claims to be. It’s still a very impressive achievement, but instead of a cell phone with which you can make calls through the public cell network, it’s more of a remote handset for a custom base station through which it can place Skype calls. Sadly the paper itself is hidden behind a journal publisher’s paywall, so we’re left to poke underneath the research group’s slightly baffling decision to use the word “Cellphone” for something that plainly isn’t, and the university PR department’s dumbing-down for the masses. Aren’t peer reviewers supposed to catch misleading descriptions as well as dodgy science?

In radio terms, it’s an analog AM two-way radio that uses a backscatter transmission technique of applying the modulation as switching to an absorbing antenna tuned to the RF source whose ambient energy is being utilized. This modulates the ambient field within the range of the device, and resulting modulated field can be received and demodulated like any other radio signal. It’s a simplex device, in that you can’t listen and talk at the same time. Other ambient power used by the circuitry is harvested by rectifying received RF and through capturing ambient light on a set of photodiodes. There is a short video explaining the system, which we’ve placed below the break.

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Using Backscatter Radio for a Soil Sensor Network

With almost 8 billion souls to feed and a changing climate to deal with, there’s never been a better time to field a meaningful “Internet of Agriculture.” But the expansive fields that make industrial-scale agriculture feasible work against the deployment of sensors and actuators because of a lack of infrastructure to power and connect everything. So a low-power radio network for soil moisture sensors is certainly a welcome development.

We can think of a lot of ways that sensors could be powered in the field. Solar comes to mind, since good exposure to the sun is usually a prerequisite for any cropland. But in practice, solar has issues, the prime one being that the plants need the sun more, and will quickly shade out low-profile soil-based sensors.

That’s why [Spyros Daskalakis] eschewed PV for his capacitive soil moisture sensors in favor of a backscatter technique very similar to that used in both the Great Seal Bug and mundane RFID tags alike. The soil sensor switches half of an etched PCB bowtie antenna in and out of a circuit at a frequency proportional to soil moisture. A carrier signal from a separate transmitter is reflected off the alternately loaded and unloaded antenna, picking up subcarriers with a frequency proportional to soil moisture. [Spyros] explains more about the sensor design and his technique for handling multiple sensors in his paper.

We really like the principles [Spyros] leveraged here, and the simplicity of the system. We can’t help but wonder what sort of synergies there are between this project and the 2015 Hackaday Prize-winning Vinduino project.

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Looking Back at QRP Transmitters

When you get to a certain age, you get unsettled by people calling “your” music oldies. That’s how a few of us felt when we saw [Mikrowave1’s] video about Retro QRP – Solid Gold Years (see below). “QRP” is the ham radio term for low power operation, and the “solid gold” years in question are the 1960s to 1980. The videox has some good stuff, including some old books and some analysis of a popular one-transistor design from that time. He even tries a few different period transistors to see which works best.

[Mikrowave1] talks about the construction techniques used in that time frame, old transistors, and some vintage test equipment. You can even see an old ARC-5 command receiver in use to listen to the transmitter. These were made for use in military aircraft and were very common as surplus.

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Chronio DIY Watch: Slick and Low Power

[Max K] has been testing the battery life of his self-designed watch under real-world conditions. Six months later, the nominally 3 V, 160 mAh CR2025 cell is reading 2.85 V, so the end is near, but that’s quite a feat for a home-engineered smart watch.

We’ve tipped our hats to the Chronio before in this Hacklet, but now that the code is available, as well as the sweet 3D-printed case files, it’s time to make your own. Why? It looks sweet, it plays a limited version of Flappy Bird (embedded below), and six month’s on a button cell is a pretty great accomplishment, considering that it’s driving a 96×96 pixel LCD display.

The Chronio is more than inspired by the Pebble watch — he based his 3D model directly on theirs — so that’s bound to draw comparisons. The Pebble is color, and has Bluetooth and everything else under the sun. But after a few weeks away from a power socket, ask a Pebble wearer what time it is. Bazinga!

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Keeping Time with a Spring Powered Integrated Circuit

Watch aficionados have a certain lust for mechanical watches. These old school designs rely on a spring that’s wound up to store energy. The movement, an intricate set of gears and other mechanical bits, ensures that the hands on the watch face rotates at the right speed. They can be considered major feats of mechanical engineering, with hundreds of pieces in an enclosure that fits on the wrist. They’re quite cheap, and you have to pay a lot for accuracy.

Quartz watches are what you usually see nowadays. They use a quartz crystal oscillator, usually running at 32.768 kHz. These watches are powered by batteries, and beat out their mechanical counterparts for accuracy. They’re also extremely cheap.

Back in 1977, a watchmaker at Seiko set off to make a mechanical watch regulated by a quartz crystal. This watch would be the best of both words. It did not become a reality until 1997, when Seiko launched the Spring Drive Movement.

A Blog To Watch goes through the design and history of the Spring Drive movement. Essentially, it uses a super low power integrated circuit, which consumes only 25 nanowatts. This IC receives power from the wound up spring, and controls an electromagnetic brake which allows the movement to be timed precisely. The writeup gives a full explanation of how the watch works, then goes through the 30 year progression from idea to product.

Once you’ve wrapped your head around that particularly awesome piece of engineering, you might want to jump into the details that make those quartz crystal resonators so useful.

[Thanks to John K. for the tip!]