Not that long ago, making a low-power and wireless weather display complete with an e-ink screen would have required a lot of work and almost certainly would have been larger than the device [Dmitry] created.
His low power e-ink weather gadget takes advantage of one of the niftier developer boards out there to create a useful and slim device that does exactly what he needs and not a lick more. It’s fast to look up weather online, but not as fast as glancing at a display in a convenient location.
The board [Dmitry] selected is a LilyGO TTGO T5s, an ESP32-based board that integrates an e-ink display, which requires no power unless being updated. It has been loaded with just enough smarts to fetch weather information using the OpenWeather API, and update the display accordingly.
Powering up the WiFi to fetch an easily-parsed JSON file and update the display only once per hour means that a battery can provide months of runtime. As a bonus, the LilyGO board even includes the ability to charge the battery, making things awfully convenient.
Soil moisture sensors are cheap and easy to interface with, to the point that combining one with an Arduino and blinking an LED when your potted plant is feeling a bit parched is a common beginners project. But what about on the long term? Outside of a simple proof of concept, what would it take to actually read the data from these sensors over the course of weeks or months?
One of the biggest challenges for wireless sensor networks is that of power. Solar panels usually produce less power than you hoped, especially small ones, and designing super low power circuits is tricky. [Strange.rand] has dropped into the low-power rabbit hole, and is designing a low-cost wireless sensor node that runs on solar power and a supercapacitor.
The main components of the sensor node is an ATMega 328P microcontroller running at 4Mhz, RFM69 radio transceiver, I2C temperature/humidity sensor, 1F supercapacitor, and a small solar panel. The radio, MCU, and sensor all run on 1.5-3.6V, but the supercap and solar panel combination can go up to 5.5V. To regulate the power to lower voltage components a low-drop voltage regulator might seem like the simplest solution, but [strange.rand] found that the 3.3V regulator was consuming an additional 20uA or more when the voltage dropped below 3.3V. Instead, he opted to eliminate the LDO, and limit the charging voltage of the capacitor to 3.6V with a comparator-based overvoltage protection circuit. Using this configuration, the circuit was able to run for 42 hours on a single charge, transmitting data once per minute while above 2.7V, and once every three minutes below that.
Another challenge was undervoltage protection. [strange.rand] discovered that the ATmega consumes an undocumented 3-5 mA when it goes into brown-out below 1.8V. The small solar panel only produces 1 mA, so the MCU would prevent the supercapacitor from charging again. He solved this with another comparator circuit to cut power to the other components.
Building a weather station isn’t too tall of an order for anyone getting into an electronics project. There are plenty of plans online, and you can even put your station on Weather Underground if it meets certain standards. These usually have access to a reliable source of power, though, and like any electronics project can get challenging quickly once it needs to work reliably in a remote location. The weather station from [Tegwyn☠Twmffat] has met this challenge though, and has been working reliably for three years now.
Getting that sort of reliability from any circuit that has to be powered by an unreliable source (solar, wind, etc.) and a battery is quite a challenge. Not only do you need to sort out the power management and make sure that you can get enough sun in the winter for your application, but you’ll need to do some extreme low power modifications to your circuitry as well. This weather station accomplishes all of that, helped by using LoRa for communication, and also comes complete with a separate hardware watchdog timer that can reboot the weather station if it loses power or hangs up for some reason.
If you’ve been looking for a weather station to build, this is a great place to start. [Tegwyn☠Twmffat] also goes through the assembly of the weather station, complete with a guy-wire-supported platform to mount it on. There are other weather stations out there too, if you need even more ideas about saving power in remote areas.
The Internet of Things is eating everything alive, and the world wants to know: how do you make a small, battery-powered, WiFi-enabled microcontroller device? This is a surprisingly difficult problem. WiFi is not optimized for low-power operations. It’s power-hungry, and there’s a lot of overhead. That said, there are microcontrollers out there with WiFi capability, but how do they hold up to running off of a battery for days, or weeks? That’s what [TvE] is exploring in a fantastic multi-part series of posts delving into low-power WiFi microcontrollers.
The idea for these experiments is set up in the first post in the series. Basically, the goal is to measure how long the ESP8266 and ESP32 will run on a battery, using various sleep modes. Both the ESP8266 and ESP32 have deep-sleep modes, a ‘sleep’ mode where the state is preserved, a ‘CPU only’ mode that turns the RF off, and various measures for sending and receiving a packet.
The takeaway from these experiments is that a battery-powered ESP8266 can’t be used for more than a week without a seriously beefy battery or a solar panel. Run times are much longer with an open network as compared to a secured network, and that security eats up a ton of power: connecting to a secure network every now and again means your ESP might only run for a day, instead of a week.
There is another option, though: the ESP32. While the ’32 is vastly more powerful and more capable than the ESP8266, it also has a few improved features that help with power consumption. Importantly, there’s a bug in the ESP8266 where it drops into modem sleep instead of light sleep about half the time. This error was fixed in the ESP32, but all that power does come at a cost. On the whole, if you’re concerned about security, the ESP32 is slightly better, simply because it does the ‘security’ part of connecting to a WiFi network faster. This is really a remarkable amount of testing that’s gone into this write-up, so if you’re developing something battery-powered with any ESP, it’s well worth the read.
Building your own weather station is a fun project in itself, but building it to be self-sufficient and off-grid adds another set of challenges to the mix. You’ll need a battery and a solar panel to power the station, which means adding at least a regulator and charge controller to your build. If the panel and battery are small, you’ll also need to make some power-saving tweaks to the code as well. (Google Translate from Italian) The tricks that [Danilo Larizza] uses in his build are useful for more than just weather stations though, they’ll be perfect for anyone trying to optimize their off-grid projects for battery and solar panel size.
When it comes to power conservation, the low-hanging fruit is plucked first. [Danilo] set the measurement intervals to as long as possible and put the microcontroller (a NodeMCU) to sleep in between. Removing the power from the sensors when the microcontroller was asleep was another easy step, but the device was still crashing overnight. Then he turned to a hardware solution and added a more efficient battery charger to the setup, which saved even more power. This is all the more impressive because the station communicates via WiFi which is notoriously difficult to run in low-power applications.
Besides the low power optimizations, the weather station itself is interesting for its relative simplicity. It could be built with things most of us have knocking around. Best of all, [Danilo] published the source code on his site, so most of the hard work has been done already. If you’re thinking he seems a little familiar, it’s because we’ve featured some of his projects before, like his cheap WiFi extender antenna and his homemade hybrid tube amplifier.
A NAS is always a handy addition to a home network, but they can be a little pricey. [Blake Burkhart] decided to create his own, prioritising budget and low power considerations, with a secondary objective to produce some router and IoT functionality on the side.
A Banana Pi R2 was a good choice to meet these requirements, being a router-based development board that also sports dual SATA connectors and gigabit Ethernet. [Blake] had some retrospective regrets about the performance of this particular SBC, but it does just fine when functioning purely as a NAS.
The enclosure for the device is a three bay hot-swap HDD module, with one of the bays gutted and used for the Banana Pi. It’s a simple idea, elegantly executed, which looks great. To access the ports of the Banana Pi, a custom acrylic side panel was laser cut, which also allowed LEDs to shine through – obligatory for any DIY server/computer build. When mounting this panel to the existing enclosure, [Blake] was reluctant to take his chances tapping the brittle acrylic, instead opting to melt the threads into the plastic with a pre-torched screw. We find that tapping acrylic is usually okay if you take it slow, but heat-tapping does sound fun.
The 12 V fan that came built into the hot-swap enclosure was too loud and awkwardly came in a non-standard size with a non-standard connector. What’s more, a buzzer alarm was triggered any time the fan was disconnected and 0 RPM was detected. [Blake]’s solution was to rewire the power pin of the connector to a 5 V rail; he found that running the fan at 5 V led to much quieter performance whilst keeping the HDDs sufficiently cool.