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Reading the temperature of your environment is pretty easy right? A quick search suggests the utterly ubiquitous DHT11, which speaks a well documented protocol and has libraries for every conceivable microcontroller and platform. Plug that into your Arduino and boom, temperature (and humidity!) readings. But the simple solution doesn’t hit every need, sometimes things need to get more esoteric.

The technique summarized by an image from Microchip Appnote AN685

For years we’ve been watching [Edward]’s heroic efforts to build accessible underwater sensing hardware. When we last heard from him he was working on improving the accuracy of his Arduino’s measurements of the humble NTC thermistor. Now the goal is the same but he has an even more surprising plan, throw the ADC out entirely and sample an analog thermistor using digital IO. It’s actually a pretty simple trick based on an intuitive observation, that microcontrollers are better at measuring time than voltage. 

The basic circuit

The circuit has a minimum of four components: a reference resistor, the thermistor, and a small capacitor with discharge resistor. To sense you configure a timer to count, and an edge interrupt to capture the value in the timer when its input toggles. One sensing cycle consists of discharging the cap through the discharge resistor, enabling the timer and interrupt, then charging it through the value to measure. The value captured from the timer will be correlated to how long it took the cap to charge above the logic-high threshold when the interrupt triggers. By comparing the time to charge through the reference against the time to charge through the thermistor you can calculate their relative resistance. And by performing a few calibration cycles at different temperatures ([Edward] suggests at least 10 degrees apart) you can anchor the measurement system to real temperature.

For all the gory details, including tips for how to save every last joule of energy, check out [Edward]’s post and the Microchip appnote AN685 he references. Besides this series [Edward]’s Cave Pearl Project has already yielded an impressive number of Hackday posts. For more great hardware writeups check out a general hardware build for a single sensing node, or the “temperature sensor” [Edward] made with no external parts at all!

The basic 16×2 LCD is an extremely popular component that we’ve seen used in more projects than we could possibly count. Part of that is because modern microcontrollers make it so easy to work with; if you’ve got an I2C variant of the display, it only takes four wires to drive it. That puts printing a line of text on one of these LCDs a step or two above blinking an LED on a digital pin on the hierarchy of beginner’s electronics projects.

What’s that? Even four wires is too many? In that case, you might be interested in this hack from [Vinod] which shows how you can drive the classic 16×2 with data and power on the same pair of wires. You’ll still need a microcontroller “backpack” for the LCD to interpret the modulated voltage, but if you’ve got an application for a simple remote display, this is definitely worth checking out.

The basic idea is to “blink” the 5 V line so quick that a capacitor on the LCD side can float the electronics over the dips in voltage. As long as one of the pins of the microcontroller is connected to the 5 V line before the capacitor, it will be able to pick up when the line goes low. With a high enough data rate and a large enough capacitor as a buffer, you’re well on the way to encoding your data to be displayed.

For the transmitting side, [Vinod] is using a Python script on his computer that’s sending out the text for the LCD over a standard USB to UART converter. That’s fed into a small circuit put together on a scrap of perfboard that triggers a MOSFET off of the UART TX line.

We actually covered the theory behind this technique years ago, but it’s always interesting to see somebody put together a real-world example. There might not be too many practical uses for this trick in the era of dirt-cheap microcontrollers bristling with I/O, but it might make a fun gag at your hackerspace.

Regular readers of Hackaday have certainly seen the work of [Jeremy Cook] at this point. Whether you remember him from his time as a writer for this fine online publication, or recognize the name from one of his impressive builds over the last few years, he’s a bona fide celebrity around these parts. In fact, he’s so mobbed with fans at events that he’s been forced to employ a robotic companion to handle distributing his personalized buttons for his own safety.

Alright, that might be something of a stretch. But [Jeremy] figured it couldn’t hurt to have an interesting piece of hardware handing out his swag at the recent Palm Bay Mini Maker Faire. Anyone can just put some stickers and buttons in a bowl on a table, but that’s hardly the hacker way. In the video after the break, he walks viewers through the design and construction of this fun gadget, which takes a couple unexpected turns and has contains more than a few useful tips which are worth the cost of admission alone.

Outwardly the 3D printed design is simple enough, and reminds us of those track kits for Matchbox cars. As you might expect, getting the buttons to slide down a printed track was easy enough. Especially when [Jeremy] filed the inside smooth to really get them moving. But the goal was to have a single button get dispensed each time the device was triggered, but that ended up being easier said than done.

The first attempt used magnets actuated by two servos, one to drop the button and the other to hold up the ones queued above it. This worked fine…at first. But [Jeremy] eventually found that as he stacked more buttons up in the track, the magnets weren’t strong enough to hold them back and they started “leaking”. This is an excellent example of how a system can work perfectly during initial testing, but break down once it hits the real world.

In this case, the solution ended up being relatively simple. [Jeremy] kept the two servos controlled by an Arduino and a capacitive sensor, but replaced the magnets with physical levers. The principle is the same, but now the system is strong enough to hold back the combined weight of the buttons in the chute. It did require him to cut into the track after it had already been assembled, but we can’t blame him for not wanting to start over.

Just like the arcade inspired candy dispenser, coming up with a unique way of handing out objects to passerby is an excellent way to turn the ordinary into a memorable event. Maybe for the next iteration he can make it so getting a button requires you to pass a hacker trivia test. Really make them work for it.

If you’ve been hanging out here at Hackaday for awhile, you’ve certainly seen projects that were based around the concept of putting a miniature computer inside the carcass of some other piece of electronics. In fact at this point it’s something of a running joke, certainly we must have seen an Arduino or Raspberry Pi shoehorned into every type of consumer gadget ever built by this point. But if you thought this would be another example of that common trope by the headline, you might be in for something of a surprise.

[zapta] didn’t put an Arduino inside this GOJO LTX-7 soap dispenser, it was already in there to begin with. That’s right, apparently we’ve hit the point that even cheap soap dispensers are now running on programmable microcontrollers. While we can’t blame those of you who are no doubt groaning and/or rolling their eyes thanks to this particular case of computational gluttony, it does mean we’re able to report with a straight face something which frankly would have passed as an April Fool’s joke in previous years: the development of an open source soap dispensing firmware.

So how does one upload a new Arduino sketch to their GOJO soap dispenser? It’s not like the thing has a USB port on the side for convenient hacking. As explained by [zapta], it involves stripping the dispenser all the way down until the electronics board is free, and then adding in a programming header to make subsequent firmware fiddling a bit easier. Writing a new firmware to the ATTiny48 powered board will require an external ISP (the Atmel AVRISP MKII was used for this hack, though any should work), but it’s otherwise pretty painless.

[zapta] has done an excellent job documenting the different components on the board, and reverse engineered enough of the critical aspects (such as the motor controller and proximity sensor) to write a new open source firmware which can be flashed to the GOJO LTX-7. Beyond allowing you to “Open Source All the Things”, using this new firmware does have some practical advantage in that you can configure how much soap is dispensed per activation. Going further, we’d be exceptionally interested in hearing about anyone who manages to come up with a firmware that enables some hitherto impossible soap dispensing trickery.

We’ve seen hacks involving dispensers of all types, from Halloween games that spit out candy to gadgets which let dogs get their own treats, but a soap dispenser hack is something truly new for us. More proof that there’s still plenty of hardware out there just waiting to be hacked!

For Hackaday readers who don’t spend their free time underwater, nitrox is a blend of nitrogen and oxygen that’s popular with scuba divers. Compared to atmospheric air, nitrox has a higher concentration of oxygen; which not only allows divers to spend more time underwater but also reduces the risk of decompression sickness. Of course when fiddling with the ratio of gases you breathe there’s a not inconsequential risk of dying, so nitrox diving requires special training and equipment to make sure the gas mixture is correct.

Divers can verify the ratio of oxygen to nitrogen in their nitrox tanks with a portable analyzer, though as you might expect, they aren’t exactly cheap. But if you’re confident in your own hacking skills, [Eunjae Im] might have the solution for divers looking to save some cash. He’s come up with an Arduino based nitrox analyzer that can be built for considerably less than the cost of a commercial unit.

Now before you get the torches lit up, we should be clear: ultimately the accuracy, and therefore safety, of this device depends on the quality of the oxygen sensor used. [Eunjae] isn’t suggesting you get a bottom of the barrel sensor for this build, and in fact links to a replacement sensor that’s intended for commercial nitrox analyzers as a way to verify the unit is up to the task. The downside is that the sensor alone runs $80. If you want to go with something cheaper, you do so at your own risk.

With a suitable sensor in hand, the project really boils down to building up an interface and enclosure for it. [Eunjae] is using an Arduino Nano, a 128×64 OLED screen, and a battery inside of a rugged waterproof case. He also added an ADS1115 16 Bit DAC between the oxygen sensor and the Arduino for fast and accurate readings over I2C. With the hardware assembled, calibrating the device is as simple as taking it outside and making sure you get an oxygen reading of 20.9% (the atmospheric normal).

While [Eunjae] is happy with his analyzer on the whole, he does see a few areas which could be improved in future revisions. The case is bulky and rather unattractive, something that could be addressed with a custom 3D printed case (though waterproofing it might be an issue). He also says the only reason he used a 9V alkaline battery was because he had it on hand, a small rechargeable battery pack would be a much more elegant solution.

We’ll go out on a limb and say that most Hackaday readers aren’t avid scuba divers. For better or for worse, we’re the sort of folks who stay in the shallow end of the pool. But when one of our ilk does dip below the waves, they really seem to go all out.

We’ve seen [Johan]’s AA-battery-sized Arduino/battery crossover before, but soon (we hope!) there will be a new version with more MIPS in the same unique form factor! The original Aarduino adhered to classic Arduino part choices and was designed to run as the third “cell” in a 3 cell battery holder to relay temperature readings via a HopeRF RFM69CW. But as [Johan] noticed, it turns out that ARM development tools are cheap now. In some cases very cheap and very open source. So why not update an outstanding design to something with a little more horsepower?

The Aarduino Zero uses the same big PTH battery terminals and follows the same pattern as the original design; the user sticks it in a battery holder for power and it uses an RFM69CW for wireless communication. But now the core is an STM32L052, a neat low power Cortex-M0+ with a little EEPROM onboard. [Johan] has also added a medium size serial flash to facilitate offline data logging or OTA firmware update. Plus there’s a slick new test fixture to go along with it all.

So how do you get one? Well… that’s the rub. It looks like when this was originally posted at the end of 2017 [Johan] was planning to launch a Crowd Supply campaign that hasn’t quite materialized yet. Until that launches the software sources for the Zero are available, and there are always the sources from the original Aarduino to check out.

The scientific community cannot always agree on how much water a person needs in a day, and since we are not Fremen, we should give it more thought than we do. For many people, remembering to take a sip now and then is all we need and the H2gO is built to remind [Angeliki Beyko] when to reach for the water bottle. A kitchen timer would probably get the job done, but we can assure you, that is not how we do things around here.

A cast silicone droplet lights up to show how much water you have drunk and pressing the center of the device means you have taken a drink. Under the hood, you find a twelve-node NeoPixel ring, a twelve millimeter momentary switch, and an Arduino Pro Mini holding it all together. A GitHub repo is linked in the article where you can find Arduino code, the droplet model, and links to all the parts. I do not think we will need a device to remind us when to use the bathroom after all this water.

Another intrepid hacker seeks to measure a person’s intake while another measures output.

If you’re the kind of person who has friends, and/or leaves the confines of the basement from time to time, we hear that these “Escape Rooms” are all the rage. Basically you get locked into a room with a couple other people and have to solve various problems and puzzles until you’ve finally made enough progress that they let you out. Which actually sounds a lot like the working conditions here at Hackaday HQ, except they occasionally slip some pizza rolls under the door for us which is nice.

Whichever side you find yourself on in one of these lighthearted hostage situations, knowledge of this multi-tag RFID lock created by [Annaane] may come in handy. By connecting multiple MFRC522 RFID readers to an Arduino Uno, she’s come up with a method of triggering a device (like an electronic door lock) only when the appropriate combination of RFID tags have been arranged. With a little imagination, this allows for some very complex puzzle scenarios which are sure to keep your prisoners enthralled until you can lower the lotion down to them.

Her code allows you to configure the type and number of RFID cards required to trigger one of the Arduino’s digital pins, which usually would be connected to a relay to fire off whatever device you want. The Arduino sketch is also setup to give “hints” to the player by way of a status LED: fast blinking let’s you know the tag scanned is wrong, and slow blinking means you don’t have enough scanned in yet.

The video after the break shows some highlights of the build, as well as a quick demonstration of how both the RFID “combination” and manual override can be used to trigger the attached relay.

Hackers do love RFID. Using them for physical access control is a fairly common project around these parts, and we’ve even seen similar setups for the digital realm.

Since its launch in 2013, the Yùn–a small Linux machine and a microcontroller in a small Arduino form factor–found its way into hundreds of thousands of projects and professional applications. Last year, we decided that it was time for a refresh and began working hard to develop a true open-source design, with more compelling features and better overall software support.

The new board, which is expected to hit the market in the second half of April, will include enhanced functionality and compatibility with its predecessor.

Why a New Yùn

The Yùn enjoyed tremendous success; however, it ended up being affected by the internal issues we dealt with over the past couple of years and support has been quite intermittent.

For example, the board was never really an open-source product and the software had some challenges that we wanted to fix, especially from a security point of view.

What’s New in Rev.2

Hardware:  

  • Much better, more robust power supply
  • New Ethernet connector with a clever mounting solution that enables the use of all possible shields with no risk for accidental short circuits
  • Horizontal USB connector to save vertical space
  • Improved USB hub

Software: 

  • Software stack updated to OpenWRT latest version, including all patches
  • SSL support on the bridge Arduino / Linux bridge

Yùn Rev.2 is scheduled to begin shipping in April. Until then, you can stay up-to-date by clicking “NOTIFY ME” on our store

[Andrew MacPherson] found out that compliments, even insincere ones, make the recipients feel better. So, he put together a thermal printer and a hilariously large button with an Arduino and created a machine that prints compliments. And where best to put a machine that prints out compliments? The local bar, where else?

An Arduino Nano clone runs the show connected to a thermal printer. The Nano clone didn’t like the 9 volt power supply, so a buck converter was used to reduce the voltage down to 5 volts for the Nano, while the printer gets the full power. During initial trials, the printer was very slow to print and it took [Andrew] a while to adjust the parameters – after tweaking the speed as well as the heating time, he was able to get the printer working without burning the paper or taking forever to print.

Once the machine was working, it was time to add a button. A large, light-up button was connected and glued to the side of the printer. More glue was used (after some “modifications” to the printer chassis) to secure a barrel connector for the power adapter.

[Andrew] decided that since he’s down at his favorite bar quite a lot, he’d set it up there. The customers could push the button and receive a compliment while drowning their sorrows. He got a friend of his who’s a copywriter to come up with some nicely written compliments to print out. The printer was such a hit that the bartender sent [Andrew] a message on Facebook saying so. If you have a thermal printer lying around, you can use this tutorial to connect it to the internet, or, if you don’t have one, you can build your own.



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