Minimal MQTT: Power and Privacy

In this installment of Minimal MQTT, I’m going to cover two loose ends: one on the sensor node side, and one on the MQTT server side. Specifically, I’ll tackle the NodeMCU’s sleep mode to reduce power and step you through bridging MQTT servers to get your data securely out of your home server and into “the cloud”, which is really just other people’s servers.

If you’re just stepping into this series now, you should really check out the other three posts, where I set up a server, then build up some sensor nodes, and then flesh-out a few ways to control everything from your phone or the web. That’s the coolest material, anyway. This last installment just refines what we’ve built on. Let’s go!

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Fixing the Terrible Range of your Cheap NRF24L01+ PA/LNA Module

nRF24L01+ PA/LNA module specs look great on paper. Wireless communication up to 1000m in a small package readily available from a variety of cheap sources in China? The hard work of software connectivity already done by a variety of open source projects? Sounds great! But if you mashed BUY and are getting maybe 1% of that range, don’t worry because thanks to these clear directions, they can be fixed.

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Identify Your Devices by Their Unintentional Radiation

RFID was supposed to revolutionize asset tracking, replacing the barcode everywhere. Or at least that was the prediction once tags got under five cents apiece. They still cost seven to fifteen cents, even in bulk, and the barcode is still sitting pretty. [Chouchang (Jack) Yang] and [Alanson Sample] of Disney Research hope to change that.

Instead of tagging every electronic device, they use whatever electromagnetic emissions the device currently produces when it’s powered up. What’s surprising is not that they can tell an iPhone from a toy lightsaber, but that they can tell the toy lightsabers apart. But apparently there’s enough manufacturing and tolerance differences from piece to piece that they appear unique most of the time.

The paper (PDF) goes through the details and procedure. The coolest bit? The sensor they use is an RTL-SDR unit with the radio-mixer front end removed and replaced with a simple transformer. This lets them feed baseband (tuning from 0 to 28.8 MHz) straight into the DAC ADC and on to the computer which does the heavy math. Sawing off the frontend of a TV tuner is a hack, for those of you out there with empty bingo cards.

If you like statistics, you’ll want to read the paper for details about how they exactly do the classification of objects, but the overview is that they first start by figuring out what type of device they’re “hearing” and then focusing on which particular one it is. The measure that they use ends up being essentially a normalized correlation.

While we’re not sure how well this will scale to thousands of devices, they get remarkably good results (around 95%) for picking one device out of five. The method won’t be robust to overclocking or underclocking of the device’s CPU, so we’re concerned about temperature and battery-voltage effects. But it’s a novel idea, and one that’s ripe for the hacker-rebuild. And for the price of an RTL-SDR, and with no additional per-tag outlay as with an RFID system, it’s pretty neat.

Thanks [Static] for the tip! Via Engadget.

Networked Solar Birdhouses Deep in the Woods

[Oitzu] in Germany wrote in to let us know about a series of short but very informative blog posts in which he describes building a series of solar-powered, networked birdhouses with the purpose of spying on the life that goes on within them. He made just one at first, then expanded to a small network of them. They work wonderfully, and [Oitzu]’s documentation will be a big help to anyone looking to implement any of the same elements – which include a Raspberry Pi in one unit as a main gateway, multiple remote units in other birdhouses taking pictures and sending those to the Pi over an nRF24L01+ based radio network, and having the Pi manage uploading those images using access to the mobile network. All with solar power.

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Solving ISP problem with a Homebrew LTE Yagi

We’ve heard reports that internet connectivity in Australia can be an iffy proposition, and [deandob] seems to back that up. At the limit of a decent DSL connection and on the fringe of LTE, [deandob] decided to optimize the wireless connection with this homebrew Yagi antenna.

Officially known as the Yagi-Uda after its two Japanese inventors from the 1920s, but generally shortened to the name of its less involved but quicker to patent inventor, the Yagi is an antenna that provides high gain in one direction. That a homebrew antenna was even necessary at all is due to [deandob]’s ISP using the 2300MHz band rather than the more popular 2400MHz – plenty of cheap 2.4GHz antennas out there, but not so much with 2.3GHz. With multiple parallel and precisely sized and spaced parasitic elements, a Yagi can be a complicated design, but luckily for [deandob] the ham radio community has a good selection of Yagi design tools available. His final design uses an aluminum rod for a boom, 2mm steel wire for reflectors and directors, and a length of coax as the driven element. The result? Better connectivity that pushes his ISP throttling limit, and no more need to mount the modem high enough in his house to use the internal antenna.

People on the fringes of internet coverage go to great lengths to get connections, like this off-grid network bridge. Or if you’d rather use a homebrew Yagi to listen to meteors, that’s possible too.

Tiny Matchbox WiFi Weather Station

Sometimes a project doesn’t have to be technically amazing to win over our hearts. [Malte]’s ESP8266-based weather station is so cute, and so nicely executed, that it’s easily worth a look. It could totally be a commercial product, and it’s smaller than a matchbox.

It combines temperature, humidity, and barometric pressure sensors on one side of a PCB, with pads for soldering a pre-built ESP8266 module on the other side. Solder it all together and flash the firmware and you’re almost all set.

The final step is to configure it to work with the network. For this, [Malte] built in a nice web-based configuration (and display) application. It also can log its data to an MQTT system, so there’s a bunch more configuration (which we’re trying to make easier) needed there, and the web frontend makes that light work. Everything, from the hardware to the firmware, and even a pre-compiled binary, is up on his GitHub. Very complete and very well done.

If you can read German, or are willing to run it through a translator, give his personal projects webpage a look as well. Good stuff here. Now all he needs is a matching nice display for inside.

Thinking of You: IoT Style

Do you have loved ones who live far away? Or do you just want an interesting starter ESP8266 project to get your feet wet? If the answer to either of these questions is “yes”, we’ve got just the project for you. [Craig Lindley] built a “thinking of you” button-and-LED display device that helps people keep in touch, in a very simple way.

We like the minimalism of the design. One party presses their button, electrons flow, WiFis WiFi, data travels through a set of tubes, and an LED far away glows a pre-arranged color. The other side can signal back to say “hi” as well. It’s a cute item to have on your desk, or wherever you spend the most time. If you’re new to all of this, you can hardly beat the circuit for its simplicity.

Yeah, you could totally just send the other person a text message or an e-mail. But then you don’t get an excuse to play around with NodeMCU, and it just lacks the personal hacker touch. The code is available in a zip file here, and if you want to stay in touch with someone other than [Craig]’s sisters, you’ll probably want to customize it a bit.