Wireless Quad Voltmeter Brings It All Together

If you’re reading Hackaday, you almost certainly have a voltmeter. Matter of fact, we wouldn’t be surprised to hear you had two of them. But what if you needed to monitor four voltage levels at once? Even if you had four meters, getting them all connected and in a convenient enough place where you can see them all at once is no small feat. In that case, it sounds like the multi-channel wireless voltmeter put together by [Alun Morris] is for you.

Built as an exercise in minimalism, this project uses an array of components that most of us already have kicking around the parts bin. For each transmitter you’ll need an ATtiny microcontroller, a nRF24L01+ radio, a small rechargeable battery, and a handful of passive components. On the receiver side, there’s an OLED screen, another nRF radio module, and an Arduino Nano. You could put everything together on scraps of perfboard like [Alun] has, but if you need something a bit more robust for long-term use, this would be a great excuse to create some custom PCBs.

While the hardware itself is pretty simple, [Alun] clearly put a lot of work into the software side. The receiver’s 128 x 32 display is able to show the voltages from four transmitters at once, complete with individual indicators for battery and signal level. When you drill down to a single transmitter, the screen will also display the minimum and maximum values. With the added resolution of the full screen display, you even get a very slick faux LCD font to ogle.

Of course, there are some pretty hard limitations on such a simple system. Each transmitter can only handle positive DC voltages between 0 and 20, and depending on the quality of the components you use and environmental considerations like temperature, the accuracy may drift over time and require recalibration. Still, if you need a way to monitor multiple voltages and potentially even bring that data onto the Internet of Things, this is definitely a project to take a look at.

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Roll Your Own Tracking

The smartphone is perhaps the signature device of our modern lives. For most of the population it is never more than an arm’s length away, it’s on your person more than any other device in your life. Smartphones are packed with all sorts of radios and ways to communicate wireless. [Amine Mansouri] built an ESP8266 based tracking device that takes advantage of this.

Most WiFi-enabled devices will send out “probe requests” frames trying to search for the SSIDs they were connected to. These packets contain the device MAC address as well as the SSIDs you’ve connected to. Using about 12 components, [Amine] laid out a small board in Eagle. By putting the ESP8266 in monitor mode, the probe frames can be logged and uploaded. The code can be updated OTA making it easy to service while in the field.

With permission from his local library, eight repeater boards were scattered throughout the building to forward the probe packets to where the tracker could pick them up. A simple web interface was built that allows the library to figure out how many people are in the library and how often they frequent the premises.

While an awesome project with open-source code on Github, it is important to stress how important is it to get permission to do this kind of tracking. While some phones implement MAC randomization, there are still many out in the wild that don’t. While this is similar to another project that listens to radio signals to determine the coming and going of ships and planes, tracking people with this sort of granularity is in a different category altogether.

Thanks [Amine] for sending this one in!

Cell Phone Signal Booster Gets Teardown And Demo

Ever wonder what was inside a cell phone booster, or what it is like to set up or use one? If so, [Kerry Wong]’s got you covered with his teardown of a Cel-Fi Go X Cell Signal Booster by Nextivity. [Kerry] isn’t just ripping apart a cheap unit for laughs; his house has very poor reception and this unit was a carefully-researched, genuine investment in better 4G connectivity.

The whole setup consists of three different pieces: the amplifier unit pictured above, and two antennas. One is an omnidirectional dome antenna for indoors, and the other is a directional log-periodic dipole array (LPDA) antenna for outdoors. Mobile phones connect to the indoor antenna, and the outdoor antenna connects to the distant cell tower. The amplifier unit uses a Bluetooth connection and an app on the mobile phone to manage settings and actively monitor the device, which works well but bizarrely doesn’t seem to employ any kind of password protection or access control whatsoever.

Overall [Kerry] is happy, and reports that his mobile phone enjoys a solid connection throughout his house, something that was simply not possible before. Watch a hands-on of the teardown along with a short demonstration in the video embedded below.

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DropController Sets The Bar For Documentation

dropController has the kind of documentation we wish would spontaneously generate itself whenever we build something. [Martyn Currey] built a robust rig for water droplet photography, and we don’t want to dismiss the hardware, but the most impressive part might be the website. It might not be very fancy, but it’s thorough and logically organized. You can find parts lists, assembly manuals, tutorials, sketches, and schematics. If only all the projects that came our way were so well detailed.

Water droplet photography is pretty cool, although freehanding it will make your patience fall faster than 9.81 m/s². The concept is that a solenoid valve will flicker open to release a drop of water, wait for a certain number of microseconds, and then trigger your DSLR via a wired remote cable. The tricky part comes from controlling as many as six valves and three flashes. We don’t have enough fingers and toes to press all those buttons.

The bill of materials contains many commonly available parts like an Arduino Nano, an LM2596 voltage regulator, some MOSFETS, an HC-06 Bluetooth module, plus standard audio connectors to hook everything up. Nothing should break the bank, but if money is not an issue, [Martyn] sells kits and complete units.

Waterdrop controllers are not the newest kids on the block, and strobe photography is a time-honored tradition.

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ESP8266 Makes A Wireless Card Reader

You can find commercial USB sticks that can also connect via WiFi. But [Neutrino] made his own using an ESP8266 married to a card reader. It all starts with the old trick of soldering a header to an SD card adapter. The USB port is still there, but it is only for power. A 3.3 V regulator and an ESP12E board round out the hardware.

Of course, the trick is the software. Starting from a few examples, he wound up providing an FTP server that you can connect to and send or receive files using that protocol.

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Hands On With A Batteryless E-Paper Display

E-paper displays are unusual in that power is only needed during a screen update. Once the display’s contents have been set, no power whatsoever is required to maintain the image. That’s pretty nifty. By making the display driver board communicate wirelessly over near-field communication (NFC) — which also provides a small amount of power — it is possible for this device to be both wireless and without any power source of its own. In a way, the technology required to do this has existed for some time, but the company Waveshare Electronics has recently made easy to use options available for sale. I ordered one of their 2.9 inch battery-less NFC displays to see how it acts.

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Hackaday Links: May 24, 2020

We’re saddened to learn of the passing of Gershon Kingsley in December 2019 at the age of 97. The composer and electronic music pioneer was not exactly a household name, but the things he did with the Moog synthesizer, especially the surprise hit “Pop Corn”, which he wrote in 1969, are sure to be familiar. The song has been covered dozens of times, in the process of which the spelling of the name changed to “Popcorn.” We’re most familiar with the 1972 cover by Hot Butter, an earworm from our youth that doesn’t hide the Moog as deeply in the backing instruments as Kingsley did in the original. Or, perhaps you prefer the cover done by a robotic glockenspiel, because robotic glockenspiel.

A few months back, we covered the audacious plan to recover the radio gear from the Titanic. At the time, the potential salvors, Atlanta-based RMS Titanic, Inc., were seeking permission to cut into the submerged remains of the Titanic‘s Marconi room to remove as much of the wireless gear as possible. A federal judge granted permission for the salvage operation last Friday, giving the company the green light to prepare an expedition for this summer. The US government, through the National Oceanic and Atmospheric Administration and the National Park Service, argued strenuously to leave the wreck be and treat it as a tomb for the 1,527 victims. For our part, we had a great discussion about the merits in the comments section of the previous article. Now that it’s a done deal, we’d love to hear what you have to say about this again.

Although life appears to be slowly returning to what passes for normal, that doesn’t mean you might not still have some cycles to spare, especially when the time spent can bolster your skillset. And so if you’re looking to adding FPGAs to your resume, check out this remote lab on FPGA vision systems offered by Bonn-Rhein-Sieg University. The setup allows you to watch lectures, download code examples, and build them on your local computer, and then upload the resulting binaries to real hardware running on the lab’s servers in Germany. It sounds like a great way to get access to FPGA hardware that you’d otherwise have a hard time laying hands on. Or, you know, you could have just come to the 2019 Hackaday Superconference.

Speaking of skill-builders, oscilloscope owners who want to sharpen their skills could do worse than to listen to the advice of a real scope jockey like Allen Wolke. He recently posted a helpful video listing the five most common reasons for your scope giving “wrong” voltage readings. Spoiler alert: the instrument is probably doing exactly what you told it to do. As a scope newbie, we found the insights very helpful, and we can imagine even seasoned users could make simple mistakes like using the wrong probe attenuation or forgetting that scope response isn’t flat across its bandwidth.

Safety tip for the gearheads among us: your jack stands might be unsafe to use. Harbor Freight, the stalwart purveyor of cheap tools, has issued a recall of two different models of its jack stands. It seems that the pawls can kick out under the right conditions, sending the supported load crashing to the ground. This qualifies as a Very Bad Day for anyone unlucky enough to be working underneath when it happens. Defective jack stands can be returned to Harbor Freight for store credit, so check your garage and be safe out there in the shop.

And finally, because everyone loves a good flame war, Ars Technica has come up with a pronunciation guide for common tech terms. We have to admit that most of these are not surprising; few among the technology literate would mispronounce “Linux” or “sudo”. We will admit to a non-fanboy level of ignorance on whether the “X” in “iOS X” was a Roman numeral or not, but learning that the “iOS” part is correctly pronounced as three syllables, not two was a bit shocking. It’s all an exercise in pedantry that reminds us of a mildly heated discussion we had around the secret Hackaday writers’ bunker and whether “a LED” or “an LED” is the correct style. If the Internet was made for anything, it was stuff like this.