Move Aside Mercury: Measuring Temperature Accurately with an RTD

Temperature is one of the most frequently measured physical quantities, and features prominently in many of our projects, from weather stations to 3D printers. Most commonly we’ll see thermistors, thermocouples, infrared sensors, or a dedicated IC used to measure temperature. It’s even possible to use only an ordinary diode, leading to some interesting techniques.

Often we only need to know the temperature within a degree Celsius or two, and any of these tools are fine. Until fairly recently, when we needed to know the temperature precisely, reliably, and over a wide range we used mercury thermometers. The devices themselves were marvels of instrumentation, but mercury is a hazardous substance, and since 2011 NIST will no longer calibrate mercury thermometers.

A typical Pt100 RTD probe

Luckily, resistance temperature detectors (RTDs) are an excellent alternative. These usually consist of very thin wires of pure platinum, and are identified by their resistance at 0 °C. For example, a Pt100 RTD has a resistance of 100 Ω at 0 °C.

An accuracy of +/- 0.15 °C at 0 °C is typical, but accuracies down to +/- 0.03 °C are available. The functional temperature range is typically quite high, with -70 °C to 200 °C being common, with some specialized probes working well over 900 °C.

It’s not uncommon for the lead wires on these probes to be a meter or more in length, and this can be a significant source of error. To account for this, you will see that RTD probes are sold in two, three, and four wire configurations. Two-wire configurations do not account for lead wire resistance, three-wire probes account for lead resistance but assume all lead wires have the same resistance, and four-wire configurations are most effective at eliminating this error.

In this article we’ll be using a 3-wire probe as it’s a good balance between cost, space, and accuracy. I found this detailed treatment of the differences between probe types useful in making this decision.

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TerraDome Gives Plants And Dinosaurs A New Home

Housing exotic plants or animals offer a great opportunity to get into the world of electronic automation. When temperature, light, and humidity ranges are crucial, sensors are your best friend. And if woodworking and other types of crafts are your thing on top, why not build it all from scratch. [MagicManu] did so with his Jurassic Park themed octagonal dome built from MDF and transparent polystyrene.

With the intention to house some exotic plants of his own, [MagicManu] equipped the dome with an Arduino powered control system that regulates the temperature and light, and displays the current sensor states on a LCD, including the humidity. For reasons of simplicity regarding wiring and isolation, the humidity itself is not automated for the time being. A fan salvaged from an old PC power supply provides proper ventilation, and in case the temperature inside the dome ever gets too high, a servo controlled set of doors that match the Jurassic Park theme, will automatically open up.

[MagicManu] documented the whole build process in a video, which you can watch after the break — in French only though. We’ve seen a similar DIY indoor gardening project earlier this year, and considering its simple yet practical application to learn about sensors, plus a growing interest in indoor gardening itself (pun fully intended), this certainly won’t be the last one.
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Internal Power Pills

Arguably the biggest hurdle to implanted electronics is in the battery. A modern mobile phone can run for a day or two without a charge, but that only needs to fit into a pocket and were its battery to enter a dangerous state it can be quickly removed from the pocket. Implantable electronics are not so easy to toss on the floor. If the danger of explosion or poison isn’t enough, batteries for implantables and ingestibles are just too big.

Researchers at MIT are working on a new technology which could move the power source outside of the body and use a wireless power transfer system to energize things inside the body. RFID implants are already tried and tested, but they also seem to be the precursor to this technology. The new implants receive multiple signals from an array of antennas, but it is not until a couple of the antennas peak simultaneously that the device can harvest enough power to activate. With a handful of antennas all supplying power, this happens regularly enough to power a device 0.1m below the skin while the antenna array is 1m from the patient. Multiple implants can use those radio waves at the same time.

The limitations of these devices will become apparent, but they could be used for releasing drugs at prescribed times, sensing body chemistry, or giving signals to the body. At this point, just being able to get the devices to turn on so far under flesh is pretty amazing.

Recently, we asked what you thought of the future of implanted technology and the comment section of that article is a treasure trove of opinions. Maybe this changes your mind or solidifies your opinion.

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Asgard: The Open Source Air Data Computer

We get a lot of awesome projects sent our way via the tip line. Well, mainly it seems like we get spam, but the emails that aren’t trying to sell us something are invariably awesome. Even so, it’s not often we get a tip that contains the magic phrase “determine Mach number” in its list of features. So to say we were interested in the Asgard Air Data Computer (ADC) is something of an understatement.

Now we’ll admit right up front: we aren’t 100% sure who the target audience for the Asgard is, but it certainly looks impressive. Team member [Erik] wrote into tip line with information about this very impressive project, which is able to perform a number of measurements on incoming air, such as true speed, viscosity, and temperature. The team says it has applications ranging from HVAC to measuring the performance of bicycles. We don’t know who’s going so fast on their bike that they need to measure air speed, but of course the hacker community never ceases to amaze us.

Even if you don’t have a jet fighter that could benefit from a high performance ADC such as Asgard, you have to be impressed by the incredible work the team has done not only designing and building it, but documenting it. From the impeccably designed 3D printed case to the stacked PCB internals, every aspect of Asgard screams professional hardware.

Data collected from Asgard can be stored on the internal micro SD if the device is to be used in stand-alone mode, or you can connect to it over USB or Bluetooth thanks to the HC-05 module. The team has even put together some scripts to merge the Asgard’s generated air data with GPS position information.

We’re all for putting high quality sensors in the hand’s of the community and seeing what they can come up with. The spirit and build quality of this project reminds us of the impressive work [Radu Motisan] has been doing with his distributed air quality sensors.

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DIY Graphene Putty Makes Super Sensitive Sensor

It is sort of an electronics rule 34 that if something occurs, someone needs to sense it. [Bblorgggg], for reasons that aren’t immediately obvious, needs to sense ants moving over trees. No kidding. How are you going to do that? His answer was to use graphene.

Actually, his super sensitive sensors mix graphene in Silly Putty, an unlikely combination that he tried after reading (on Hackaday, no less) about similar experiments at Trinity College resulting in Gputty. The Gputty was highly sensitive to pressure, and so it appears is his DIY version called Goophene. At Trinity they claimed to be able to record the footsteps of a spider, so detecting ant stomping didn’t seem too far-fetched. You can see a video of the result, below.

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Shah Selbe: Science in the World’s Wildest Places

When we think of building research hardware, lab coats and pristine workbenches come to mind. Shah Selbe used to do something kind of like that when he was engineering satellite propulsion systems. But after putting twelve of them into space, he ditched the office gig and took his gear to some of the wildest places on earth. He’s an explorer and fellow with the National Geographic Society, and at the Hackaday Superconference he shared his experiences building research hardware that gathers data in incredibly remote places.

Shah makes a really good point about two very different trends in our world over the past several decades. While we’ve had unparalleled technological growth, we’ve also seen horrifying wildlife trends to the point that some scientists believe we’re currently in a sixth mass extinction event. But to know that for sure, and look for ways to prevent and reverse it, we need reliable data. This is a fascinating problem because the world is huge, and we simply can’t monitor everything.

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Intellibuoy Keeps Track of the Water

With world oceans ranging in cleanliness from pretty nasty to OMG, we need to get a handle on what exactly is going on. High School students from Hackensack, NJ built the Intellibuoy, a floating water quality sensor. The buoy has an anemometer and digital rain gauge up top, as well as a LED beacon to comply with maritime regulations.

Flotation is provided by a framework of sealed 3/4″ and 3″ PVC pipes that look strong enough to protect the electronics from a casual boat-bump. High above the water (under ideal conditions) there is the waterproof control box, packing two Arduino UNOs which listen to the sensors. A turbidity sensor measures how much silt is in the water; the other sensors measure Ph, dissolved oxygen, and temperature. The sensor pod is suspended inside a double ring of PVC for maximum protection. Each ‘Duino also has a SD card shield that stores the data of the respective sensors.

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