Wireless Hacks

1047 Articles

3D Printed WiFi Reflectors Custom Designed For The Building

November 18, 2017 by 35 Comments

Are you a wizard at antenna design? Chances are you’ve never even given it a try, but this tool could change that. Most home-made WiFi signal boosting antenna plans around the Internet share one feature: they are directional antennas or reflectors. But WiPrint is a tool for designing custom WiFi reflectors that map to the specific application.

If we want to increase the signal strength in two or three different locations the traditional solution is an omnidirectional antenna. The problem is, although a good omnidirectional antenna increases the signal power in those locations we want, it also increases the signal power where we don’t want.

A team of researchers led by Dartmouth College created WiPrint to allow users to input a floor plan, the location of the WiFi access point and a desired signal map into the system. The software uses an optimization algorithm to produce a custom reflector shape for that floor plan. The reflector can then be fabricated and placed next to the access point antenna to reflect and concentrate the signal in the specified area, while decreasing signal strength outside of it. The best thing is: you can actually 3D print the reflector and just glue tin foil on it!

The results show that optimized reflectors can weaken or enhance signals in target areas by up to 10 or 6 dB, respectively, and resulting in throughput changes by up to -63.3% or 55.1%. That is not the only advantage, as the researchers point out:

Our approach provides four benefits. First, it provides strong physical security by limiting the physical reach of wireless signals, hence creating a virtual wall for wireless signals. Second, it relies on a low-cost ($35), reproducible 3D reflector, which can be easily replaced upon substantial changes in the environment or coverage requirement. Third, it offers an easily accessible and easy-to-configure solution to non-expert users. Users only need to specify coverage requirements and a coarse environment model, with which our system computes a reflector shape tailored to the built environment. Finally, it is applicable to commodity low-end Wi-Fi APs without directional or multiple antennas.

The sad part is that, for now, no software is available. The study and results have just been presented at ACM’s BuildSys 2017. It would be great to see something like this open-sourced. Meanwhile, this is further proof that [Brian Benchoff] knew what he was doing when he told you to use duct tape for superior WiFi range.

Raspberry Pi Learns Slow Morse Code

November 13, 2017 by 11 Comments

It wasn’t long ago that you needed to know Morse code to be a ham radio operator. That requirement has gone in most places, but code is still useful and many hams use it, especially hams that like to hack. Now, hams are using the Raspberry Pi to receive highly readable Morse code using very low power. The software is QrssPiG and it can process audio or use a cheap SDR dongle.

There are a few reasons code performs better than voice and many other modes. First, building transmitters for Morse is very simple. In addition, Morse code is highly readable, even under poor conditions. This is partly because it is extremely narrow bandwidth and partly because your brain is an amazing signal processor.

Like most communication methods, the slower you go the easier it is to get a signal through. In ham radio parlance, QRS means “send slower”, so QRSS has come to mean mean “send very slowly”. So hams are using very slow code, and listening for it using computerized methods. Because the data rate is so slow, the computer has time to do extreme methods to recover the signal — essentially, it can employ an extremely narrow filter. Having a QRSS signal detected around the world from a transmitter running much less than a watt is quite common. You can see a video introduction to the mode from [K6BFA] and [KI4WKZ], below.

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Repair Job Fixes Compressor, Gets It Online

November 5, 2017 by 35 Comments

We’ll never cease to be amazed at the things people try to put on the Internet of Things. Some are no-brainers, like thermostats, security cameras, and garage door openers. Others, like washing machines and refrigerators, are a little on the iffy side, but you can still make a case for them. But an IoT air compressor? What’s the justification for such a thing?

As it turns out, [Boris van Galvin] had a pretty decent reason for his compressor hacks, and it appears that the IoT aspect was one of those “why not?” things. Having suffered the second failure of his compressor’s mechanical pressure switch in a year, and unwilling to throw good money after the $120 that went into replacing the first contactor, [Boris] looked for a cheaper and more interesting way to control the compressor. An ESP8266 dev board made interfacing the analog pressure sensor a snap, and while he was at it, [Boris] added a web interface with a nice graphical air pressure gauge and some on-off controls. Now he can set the pressure using his phone and switch it off in the middle of the night without going outside. That’s an IoT win right there.

No air compressor? No worries — build your own from an old fridge. The non-IoT kind, preferably.

Review: New 3G And Cat-M1 Cellular Hardware From Hologram

October 5, 2017 by 31 Comments

In July we reported on the launch of the Hologram developer program that offered a free SIM card and a small amount of monthly cellular data for those who wanted to build connectivity into their prototypes. Today, Hologram has launched some new hardware to go along with that program.

Nova is a cellular modem in a USB thumb drive form factor. It ships in a little box with a PCB that hosts the u-blox cellular module, two different antennas, a plastic enclosure, and a SIM card. The product is aimed at those building connected devices around single-board computers, making it easy to plug Nova in and get connected quickly.

This device that Hologram sent me is a 3G modem. They have something like 1,000 of them available to ship starting today, but what I find really exciting is that there is another flavor of Nova that looks the same but hosts a Cat-M1 version of the u-blox module. This is a Low Power Wide Area Network technology built on the LTE network. We’ve seen 2G and 3G modems available for some time now, but if go that route you’re building a product around a network which has an end-of-life concern.

Cat-M1 will be around for much longer and it is designed to be low power and utilizes a narrower bandwidth for less radio-on time. I asked Hologram for some power comparison estimates between the two technologies:

AVERAGE current consumption comparisons:

Cat-M1: as low as 100 mA while transmitting and never more than 190 mA
Equivalent 3G: as high as 680 mA while transmitting

PEAK current consumption comparisons (these are typically filtered through capacitors so the power supply doesn’t ever witness these values, and they are only momentary):

Cat-M1: Less than 490 mA
Equivalent 3G: As high as 1550 mA

This is an exciting development because we haven’t yet seen LTE radios available for devices — of course there are hotspots but those are certainly not optimized for low power or inclusion in a product. But if you know your ESP8266 WiFi specs you know that those figures above put Cat-M1 on a similar power budget and in the realm of battery-operated devices.

The Cat-M1 Nova can be ordered beginning today, should ship in limited quantities within weeks, with wider availability by the end of the year. If you can’t get one in the first wave, the 3G Nova is a direct stand-in from the software side of things.

I suspect we’ll see a lot of interest in Cat-M1 technology moving forward simply because of the the technology promises lower power and longer support. (I’m trying to avoid using the term IoT… oops, there it is.) For today, let’s take a look at the 3G version of the new hardware and the service that supports it.

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Datalogger Uses ESP32 And ESP8266 Low Power Modes

September 24, 2017 by 64 Comments

[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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Piezomagnetic Trick Shrinks 2.5 GHz Antennas

September 15, 2017 by 20 Comments

To a ham radio operator used to “short”-wave antennas with lengths listed in tens of meters, the tiny antennas used in the gigahertz bands barely even register. But if your goal is making radio electronics that’s small enough to swallow, an antenna of a few centimeters is too big. Physics determines plausible antenna sizes, and there’s no way around that, but a large group of researchers and engineers have found a way of side-stepping the problem: resonating a nano-antenna acoustically instead of electromagnetically.

Normal antennas are tuned to some extent to the frequency that you want to pick up. Since the wavelength of a 2.5 GHz electromagnetic wave in free space is 120 cm mm, most practical antennas need a wire in the 12-60 cm mm range to bounce signals back and forth. The trick in the paper is to use a special piezomagnetic material as the antenna. Incoming radio waves get quickly turned into acoustic waves — physical movement in the nano-crystals. Since these sound waves travel a lot slower than the speed of light, they resonate off the walls of the crystal over a much shorter distance. A piezoelectric film layer turns these vibrations back into electrical signals.

Ceramic chip antennas use a similar trick. There, electromagnetic waves are slowed down inside the high-permittivity ceramic. But chip antennas are just slowing down EM waves, whereas the research demonstrated here is converting the EM to sound waves, which travel many orders of magnitude slower. Nice trick.

Granted, significant material science derring-do makes this possible, and you’re not going to be fabricating your own nanoscale piezomagnetic antennas any time soon, but with everything but the antenna getting nano-ified, it’s exciting to think of a future where the antennas can be baked directly into the IC.

Thanks [Ostracus] for the tip in the comments of this post on antenna basics. Via [Science Magazine].

DIY Wireless Sprinkler System? Don’t Mind If I Do.

September 5, 2017 by 13 Comments

What to do once you have a sprinkler system installed on your property: buy a sprinkler control system or make your own? The latter, obviously.

[danaman] was determined to hack together a cheap, IoT-enabled system but it wasn’t easy — taking the better part of a year to get working. Instead of starting right from scratch, he used the open-source Sustainable Irrigation Platform(SIP) control software — a Python sprinkler scheduler with some features [danman] was looking for(eg: it won’t activate if there’s rain in the forecast). Since he wasn’t running it with a Raspberry Pi as recommended, [danman] wrote a Python plugin that runs on his home server as a daemon which listens to TCP port 20000 for connections and then updates the relevant relays. Ok, software done; on to the relay controller box!

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