#FreePCB via Twitter to 2 random RTs

via Dangerous Prototypes

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Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:

  • Hate Twitter and Facebook? Free PCB Sunday is the classic PCB giveaway. Catch it every Sunday, right here on the blog
  • Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
  • Facebook PCB Friday. Free PCBs will be your friend for the weekend

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Check out how we mail PCBs worldwide video.
  • We’ll contact you via Twitter with a coupon code for the PCB drawer.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.

We try to stagger free PCB posts so every time zone has a chance to participate, but the best way to see it first is to subscribe to the RSS feed, follow us on Twitter, or like us on Facebook.

A look back at CTC Valencia Fair 2018

via Arduino Blog

On April 18th, a team from Arduino Education made it to the museum Ciudad de las Artes y las Ciencias in Valencia to participate in the CTC Valencia Fair. A total of 1,200 students (out of 1,500 people in attendance) participated in the five-hour-long event where the students exhibited what they had been producing over the last couple of months.

CTC, the Creative Technologies in the Classroom initiative

CTC started as a project in the region of Castilla La Mancha in Spain. I was asked what kind of process could be implemented in order to bring teachers and school up to speed with new educational technologies. Back then, in 2012, I had been teaching students from many different disciplines, mostly at the university level: interaction design, medicine, engineering, product design, mathematics, multimedia, fine arts… I had also been working with upper secondary school teachers from Spain, Argentina, and Sweden in the creation of small curriculums introducing interactive technologies a part of more transversal teaching in subjects like science and design.

When asked by the people in charge at the regional centre for educators in Castilla La Mancha, I suggested a quick iterative design process that began with a collective survey to teachers in 25 schools and followed by a curriculum suggestion on topics that they considered relevant. The most complex aspect in this process was how to design interventions in the way of implementing this programme so that I could incorporate the teachers’ as well as the students’ opinions and debug the content as we went. CTC has over 25 different mid-size experiments designed to help a class get acquainted to work in a project-based learning methodology through an iterative process.

The first CTC fair brought together over 400 students from all over Castilla La Mancha that presented 100-plus projects. Almost five years later, we have witnessed yet another incredible fair with very nice results, only this time in Valencia.

What has changed

CTC now includes experiments with wireless technology, accelerometers, capacitive sensing, motors, lights, and other interesting tricks, thanks to using the Arduino 101 board that comes with BLE, an IMU, and some other goodies. Students are introduced to programming using Processing and the Arduino IDE. But not everything is coding, given our pedagogic approach, they learn how to work in groups, search for technical information, organize time, and present their results…

On the Arduino side, we have jumped from having a good old WordPress site to enable communication between the students, to a full-fledged platform that is being augmented with new materials and courses on a yearly basis. The content works for both the classic IDE and the more modern Create IDE. At the same time, we have implemented a hotline where teachers can ask questions directly to Arduino’s support specialists. Of course, there is a forum just for teachers to talk to one another and the Arduino forum still supporting them; but we have learned that teachers like one-to-one communication because each school is somehow different in terms of equipment, network facilities, classrooms and policies, and social environment–teachers, students, and their families.

We have learned about complex deployments; for example, in Valencia there is a special Linux distribution called Lliurex that we had to hack in order to get the IDE running properly. During a previous project in Andalucia, teachers had no administration password to the computers! Well, we did figure things out and got the project to work. So big kudos to our support team that had to get out the hacker hoodie and code a clever solution!

Also, for the CTC webinars we make on a bi-weekly basis, we have changed our online seminar backend to have a much more efficient one. Now our calls allow full interaction with the participants that can be invited to talk and share screens when needed instead of simply having a chat line back.

Valencia is cool, isn’t it?

We had a CTC fair at the Ciudad de las Artes y las Ciencias, a museum by Santiago Calatrava in the shape of a huge boat put upside-down. There are fountains surrounding the building, the weather was amazing (remember I am coming from Sweden, where we just had the worst winter in 10 years, so anything over 15°C is good at this point), the organizers from CEFIRE (the teacher organization in Valencia’s region) made a great preparation of the location, schools arrived on time, the show went fine-great-FABULOUS… so yes, Valencia is cool, and the so was the CTC fair.

On stage we could see almost 30 projects being presented by the students, while we conducted a two and a half-hour livecast for those interested in seeing the projects from anywhere in the world. We held 15 interviews, but unfortunately we couldn’t show everything happening, considering that there were a more than 150 projects on display!

The following video is a summary of livestream from the museum; for your benefit, we have chosen some highlights of the broadcast I conducted throughout the day.

The interviews were conducted in Spanish, which is another reason for the summary; but if you are interested in the actual interviews, check out the following video.

Some seriously nice projects

I cannot stop being surprised by the amount of creativity students show when making projects. Even if I attend an average of five events of this nature per year, I keep on finding projects that make an impression in me. Students are always challenging any pre-conceptions I might have about what could be done with something as simple as an Arduino board. The one thing teachers keep on saying again and again is that it was them, the students, that pushed the process forward, that once they got started with the course, it was hard not to get carried away by the students initiative. The role of the teachers is playing the realist, trying to make sure the projects come to an end. That said, here some of the things I saw while walking around in the fair.

Probably the most impressive project I came across was a model of the Hogwart’s castle inspired by the Harry Potter movies. It took the students four months to build the entire project. It was a replica of the castle, so heavy that it needed four people to carry it around. It had dragons flying around one tower, the lights could be turned on and off… there was even a fountain with running water! The whole mode could be controlled via Bluetooth from an Android tablet. In total, the model took three months to construct, the students said, while making the electronics and software work took one month.

On the other side of the spectrum, I could play with a small arm wrestling toy made by a single student that took only 5 hours to build. You can check out the interview with the student in the above-posted videos. While the project seems to be simple, it is clear that the student had become quite knowledgeable in the craft of making projects, since he had figured everything for the project on his own without any external help.

One last project I would like to talk about was a small drawing machine comprised of mechanics from DVD drives that could replicate small drawings (less than 10x10cm big) using a pen. The students explained that it barely worked the night before, but that they finally figured out the calibration process minutes before leaving for the fair. The results, as you can see on the video interviews, are quite remarkable. They can export drawings using the open source program Inkscape in a format (G-code) their machine can understand, this allows them to trace any kind of vectorized drawing and reproduce it with their machine.

There were a lot more projects, take a look at the videos and pictures in this blog post. We will be presenting some others as part of the Arduino Livecast series in the the future. If you want to know more, just subscribe to Arduino’s YouTube channel and you will get weekly notifications on our videos.

Acknowledgements

The CTC Valencia project has been possible thanks to the generous contribution of EduCaixa, the on-site collaboration of the technical body at CEFIRE, the kind support of the regional government of Valencia – the Generalitat -, and the help of our old friend Ultralab.

From everyone involved in the project, big thanks to Ismael and Oscar, who believed in the project and pushed for it. Personally I want to thank Nerea who coordinated the project, and Roxana who was there making it happen from Arduino on a weekly basis; also Carla and Carlos who covered up when needed. Finally to Laura, who worked long evenings on top of everything else to make all of graphics needed for the fair.

At a more technical level, we have a new revision to the look and feel of the CTC project site coming, and it is looking awesome. Marcus, Gabrielle, Luca and everyone working with the UX in Arduino are creating one of the best-looking educational experiences ever. If not only the content is good, but if it feels good and looks good, then the experience will be excellent!

Do you want CTC in your world?

If you want to be part of the CTC initiative, visit Arduino Education’s website, subscribe to the Arduino Education Newsletter [at the bottom of that site], or send us a request for more information via email: ctc.101@arduino.cc.

[Photos by Pablo Ortuño]

Tackling climate change and helping the community

via Raspberry Pi

In today’s guest post, seventh-grade students Evan Callas, Will Ross, Tyler Fallon, and Kyle Fugate share their story of using the Raspberry Pi Oracle Weather Station in their Innovation Lab class, headed by Raspberry Pi Certified Educator Chris Aviles.

Raspberry Pi Certified Educator Chris Aviles Innovation Lab Oracle Weather Station

United Nations Sustainable Goals

The past couple of weeks in our Innovation Lab class, our teacher, Mr Aviles, has challenged us students to design a project that helps solve one of the United Nations Sustainable Goals. We chose Climate Action. Innovation Lab is a class that gives students the opportunity to learn about where the crossroads of technology, the environment, and entrepreneurship meet. Everyone takes their own paths in innovation and learns about the environment using project-based learning.

Raspberry Pi Certified Educator Chris Aviles Innovation Lab Oracle Weather Station

Raspberry Pi Oracle Weather Station

For our climate change challenge, we decided to build a Raspberry Pi Oracle Weather Station. Tackling the issues of climate change in a way that helps our community stood out to us because we knew with the help of this weather station we can send the local data to farmers and fishermen in town. Recent changes in climate have been affecting farmers’ crops. Unexpected rain, heat, and other unusual weather patterns can completely destabilize the natural growth of the plants and destroy their crops altogether. The amount of labour output needed by farmers has also significantly increased, forcing farmers to grow more food on less resources. By using our Raspberry Pi Oracle Weather Station to alert local farmers, they can be more prepared and aware of the weather, leading to better crops and safe boating.

Raspberry Pi Certified Educator Chris Aviles Innovation Lab Oracle Weather Station

Growing teamwork and coding skills

The process of setting up our weather station was fun and simple. Raspberry Pi made the instructions very easy to understand and read, which was very helpful for our team who had little experience in coding or physical computing. We enjoyed working together as a team and were happy to be growing our teamwork skills.

Once we constructed and coded the weather station, we learned that we needed to support the station with PVC pipes. After we completed these steps, we brought the weather station up to the roof of the school and began collecting data. Our information is currently being sent to the Initial State dashboard so that we can share the information with anyone interested. This information will also be recorded and seen by other schools, businesses, and others from around the world who are using the weather station. For example, we can see the weather in countries such as France, Greece and Italy.

Raspberry Pi Certified Educator Chris Aviles Innovation Lab Oracle Weather Station

Raspberry Pi allows us to build these amazing projects that help us to enjoy coding and physical computing in a fun, engaging, and impactful way. We picked climate change because we care about our community and would like to make a substantial contribution to our town, Fair Haven, New Jersey. It is not every day that kids are given these kinds of opportunities, and we are very lucky and grateful to go to a school and learn from a teacher where these opportunities are given to us. Thanks, Mr Aviles!

To see more awesome projects by Mr Avile’s class, you can keep up with him on his blog and follow him on Twitter.

The post Tackling climate change and helping the community appeared first on Raspberry Pi.

DIY 3D-Printed Ink Stamps

via SparkFun: Commerce Blog

My adventures in 3D printing have taken me from DIY cookie cutters to the next logical place: DIY 3D-Printed Stamps. As an avid crafter, I am beyond excited about my newfound ability to make customized crafting tools using the 3D printer.

Making 3D-printed stamps is not as simple as designing a model and hitting “print.” In order to imitate the rubbery material of a stamp itself, as well as the wooden handle, I needed to use two kinds of filament. For the handle, I used regular ABS, which is a hard plastic and common 3D-printing material. For the stamp, I used a special flexible filament called NinjaFlex. This rubbery material is perfect for printing flexible or softer objects. Given the inherent qualities of the material, it requires a specific extruder for your printer. Here at SparkFun we use LulzBot 3D printers, so I picked up their special FlexyStruder Tool Head. If you are thinking about buying a new tool head for your LulzBot printer to interface with flexible materials, I would actually recommend the Aerostruder Tool Head as it can print both felxible materials, like NinjaFlex, and normal hard plastics like ABS/PLA.

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I had to work through a few small challenges in this project. The first issue I encountered was the natural texture of the 3D print on the stamp face. The grooves between the fine lines held on to the ink, and when I would press the stamp to paper, the texture came through clear as day. In order to combat this, I came up with a surface melting technique. I put my clothing iron on high, covered it with a piece of parchment paper, and pressed the face of my stamp against the iron face through the parchment paper. This effectively removed the linear texture from the stamp and offered a smooth surface. I lightly sanded the surface to give it a bit of tooth to hold onto the ink.

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I also found that using a 100 percent infill for the rubbery part of the stamp gave it a stronger structure that was easier to work with when using it in practice. With a 20 - 50 percent infill, the stamp was kind of wobbly when I pressed it against paper, and I was getting results that were not as sharp as I hoped. With the higher infill, the stamp was more rigid and stable against the paper and the results were crisp.

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I have so many ideas for different stamps I can barely pick which one to make next. Let us know what you think about this project in the comments below!

Interested in learning more about at-home 3D printing? Check out SparkFun’s 3D printers and supplies.

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Paper As a Substrate for Circuits

via Hacking – bunnie's blog

I’ve spent a considerable portion of my time in the past couple of years helping to develop products for Chibitronics, a startup that blends two unlikely bedfellows together, papercraft and electronics, to create paper circuits. The primary emphasis of Chibitronics is creating a more friendly way to learn, design and create electronics. Because of this, much of the material relating to paper circuitry on the Internet looks more like art than electronics.

This belies the capabilities of paper as an engineering material. Google’s Cardboard and Nintendo’s Labo are mainstream examples of paper’s extraordinary capability as an engineering material. Prof. Nadya Peek at the University of Washington has written several academic papers on building multi-axis CNC machines using paper products.

A couple points to clarify up top: for the sake of brevity, I will use the term “paper” instead of “paper and/or cardboard”, analogous to how one would refer to a PCB made of Kapton or FR-4 both as printed circuits. Furthermore, while Chibitronics focuses on providing solderless solutions for younger learners, the techniques shared in this post targets engineers who have the skill to routinely assemble modern SMT designs. I assume you’ve got a good soldering iron and a microscope, and you know how to use both (or perhaps are up to the challenge of learning how to use them better).

The Argument for Paper
For prototyping and learning the principles of electronics, paper has several distinct advantages over breadboards.

The primary advantage of a breadboard is that it’s solderless, and as a result you can re-use the components. This made a lot more sense back when a 6502 used to cost $25 in 1975 ($115 in 2018 money), but today the wire jumper kit for a solderless breadboard can cost more than the microcontroller. Considering also the relatively high cost of a solderless breadboard and the relatively low value of the parts, you’re probably better off buying extra parts and soldering them to disposable paper substrates than purchasing a re-usable solderless breadboard for all but the simplest of circuits.


Electronic components used to be really expensive, so you wanted to re-use them as much as possible. The 8-bit 6502 at $115 (adjusted for inflation) was considerably cheaper than its competition in 1975 (from Wikipedia).

On the other hand, paper has a number of important advantages. The first is that it’s compatible with surface mount ICs. This is increasingly important as chip vendors have largely abandoned DIP packages in favor of SMT packages: mobile computing represents the highest demand for chips, and SMT packages beat DIP packages in both thermal and parasitic electrical characteristics. So if you want a part that wasn’t designed by someone wearing a jean jacket and highwaters, you’re probably going to find it only available in SMT.


The evolution of packaging (from left to right): DIP, SOIC, TSSOP, and WLCSP. The WLCSP is shown upside-down so you can see how solder balls are applied directly to a naked silicon chip. It’s the asymptotic size limit of packaging, and is quite popular in mobile phones today.

The second and perhaps more important advantage is that it’s electrically similar to a printed circuit substrate. Breadboards feature long, loose wires with no sense of impedance control at all. Printed circuits are 2.5-D (e.g. planar multi-layer) constructions that feature short, flat wires and often times ground planes that enable impedance control. Paper circuit construction is much closer to that of a printed circuit, in that flat copper tape forms traces that can be layered on top of each other (using non-conductive tape to isolate the layers). Furthermore, when laid on top of a controlled-thickness substrate such as cardboard, the reverse side can be covered with a plane of copper tape, thus allowing for impedance control. The exact same equations govern impedance control in a paper circuit constructed with a ground plane as a printed circuit constructed with a ground plane – just the constants are different.


This equation works for both FR-4 and cardboard. Just plug in the corresponding ε, w, t, and h. From rfcafe.com.

This means you can construct RF circuits using paper electronic techniques — from directional couplers to antennae to amplifiers. The low parasitics of copper tape also means you can construct demanding circuits that would be virtually impossible to breadboard, such as high-power switching regulators, where ripple performance is heavily impacted by parasitic resistance and inductance in the ground connections.


A 10W, 5V buck regulator laid out with paper electronics. The final layout closely resembles the datasheet layout example and performs smoothly at 2A load; this circuit probably wouldn’t regulate properly at high loads if built with a SMT-to-DIP breakout and a breadboard.

In addition to impedance control and lower parasitics, the use of copper tape to form planes means paper electronics can push the power envelope by leveraging copper plans as heatsinks. This is an important technique in FR-4 based PCBs; in fact, for many chips, the dominant path for heat to escape a chip is not through the package surface, but instead through the pins and package traces.


Copper conducts heat about 1000x better than plastic, so even the tiny metal pins on a chip can conduct heat more efficiently from an IC than the surface of the plastic package. Flip-chip on lead frame graphic adapted from Electronic Design.

The copper which forms the pins and lead frames of a chip package is a vastly superior (about 1000x better) heat conductor compared to air or plastic, so a cheap and effective method of heatsinking is to lay out a large plane of copper connected to the chip. Below is an example of a 60-watt power driver that I built using paper electronics, leveraging a copper tape plane plus extra foil as heat sinks.


That’s a 12A power transistor, and this heater control circuit can use much of that ampacity. Additional copper foil was soldered on for extra heat sinking. The equivalent in DIP/TO packages might melt a breadboard during normal operation.

Paper electronics has one additional advantage that is unique to itself: the ability to fold and bend into 3-dimensional shapes. This is something that neither breadboards nor FR-4 circuit boards can readily do. Normally, circuit boards that can bend require more exotic processes like rigi-flex or flex PCB manufacture; but paper supports this natively. Artists take advantage of this property to create stunning electronic origami, but engineers can also use this property to great effect.


Trox Circuit Study 05 by Jonathan Bobrow, from the Paper Curiosities gallery

The ability to fold a sheet of cardboard or paper means that paper circuits can be slotted around tight corners and conformed to irregular or flexible surfaces, eliminating connectors and creating a thinner, sleeker packages. Need a test point? Cut a hanging tab out of your substrate, and you’ve got a fold-up point where you can attach an alligator clip!

Using Paper to Facilitate Prototyping with SMT
Here’s a detailed example of the construction techniques I use when working with paper electronics. I built a breakout board to solve a common problem: matching voltages between chips. Older chips are powered by 5V, newer ones by 1.8V or lower, and none of these are a match for your typical 3.3V-tolerante microcontroller. There are small circuits called “level shifters” that can safely take digital signals of one signal swing to another range. The problem is that most of the “good” ICs today come only in SMT packages, so if you’re prototyping on a breadboard or using alligator clips to cobble something together, you’ve got very limited options. In fact, one of my “go-to” ICs for this purpose is the 74LVC1T45; it’s capable of 420Mbps data rates, and can convert anywhere from 1.65V to 5.5V in a direction that can be selected using an input pin. The packaging options for this chip range from a DSBGA to a SOT-23 – clearly a chip targeted at the mobile phone generation, and not meant for breadboarding.

However, I’m often confronted with the problem of driving a WS281B LED strip from the I/O of a modern microprocessor. WS2812B LEDs operate off of 5V, and expect 5V CMOS levels; and no modern microprocessor can produce that. You can usually get away with driving a single WS2812B with a 3.3V-compatible I/O, but if you’re driving a long chain of them you’ll start to see glitches down the chain because of degraded timing margins due to improper voltage levels at the head of the chain. So, I’d love to have a little breakout board that adapts a SOT-23-sized 74LVC1T45 to an alligator-clip friendly format.

Instead of laying out a PCB, fabbing a one-off, and soldering it together, I took a piece of cardboard and built a breakout board in under an hour. Furthermore, because I can bend cardboard, I can make my breakout board dual-purpose: I can add pins to it that make it breadboard-compatible, while having fold-up “wings” for alligator clips. Without the ability to fold up, the alligator clip extensions would block access to the breadboard connections. Below are some shots of the finished project.


Native comments plus on-board decoupling caps makes this simple to use, even with long alligator clips


DIP pins coming out the bottom side allow this to be used in a breadboard, too


SMT, DIP, and alligator clips all coexisting in a single breakout — easy to do with paper!

The first step in making a paper circuit is to grab a suitable piece of cardboard. I’ve come to really enjoy the cardboard used to make high-quality mats for picture framing. It’s about 1.3-1.4mm thick, which is fairly similar to FR-4 thickness, and its laminate structure means you can score one side and make accurate folds into the third dimension. The material is also robust to soldering temperatures, and its dense fiber construction and surface coating keeps the paper surface intact when pulling off mild adhesives, like the ones found on copper tape.

I’ll then cut out a square about the size I think it needs to be. I’ll usually cut a little larger, because it’s trivial to trim it back later on, but janky to tape on an extension if it’s too small.

Then, I lay the components on top and sketch a layout – this one’s pretty simple, I just note where I want the SOT-23 to go, and where the breakouts should run to.

Once I’m happy with the sketch, I’ll lay down copper tape, solder on the components, and then fold/bend the breakout into the final shape.

The trickiest and most important technique to master is how to mate the copper tape to the tiny pins of the SOT-23 (or other SMT) package. I use a trick that Dr. Jie Qi taught me, which is to cut a set of triangular notches into the tip of a wider piece of copper tape of roughly the right pitch. The triangular shape lets you adjust the size of the landing pad by simply changing the gap between the two ends of the tape, alleviating the need for precise alignment. Then, once the component is soldered to the wide piece of copper tape, you take a knife and cut the tape into individual traces – voilà, an SMT breakout is born!

A lot of this is better shown not told, so I’ve created a little video, below, that walks you through the entire process of building the breakout.

Try Something Different, and You Might be Rewarded!
Paper as an electrical engineering material is something I would never have thought of on my own – I grew up prototyping with breadboards and wire-wrap, and I was prejudiced against paper as a cheap, throwaway material that I incorrectly thought was too flammable to solder. Instead, I spent hundreds of dollars on breadboards and wire wrap sockets, when I could have made do with much cheaper materials. Indeed, there is an irrational psychology that regards expensive things as inherently better than cheap things, which means cheap options are often overlooked in the search for solutions to hard problems.

But this is why it’s important to collaborate with experts outside your normal field of expertise – the further outside, the better. In addition to being a great engineer, Jie Qi is a prodigious artist. Through our Chibitronics collaboration, she’s added so much more depth and dimension to my world on so many fronts. She’s imparted upon me invaluable gifts of skills and perspectives that I would never have developed otherwise.

It’s my hope that by sharing a little more about paper electronics, I can bring a fresh perspective on old problems while broadening awareness and getting more users to improve upon the basics. After all, this is a new area, and we’re just starting to explore the possibilities.

Interested in hacking paper electronics? Check out the Chibitronics Creative Coding Kit, and the Love to Code product line. It’s a gentle introduction to paper electronics targeted at newcomers, but it’s also open source, so you can take it as far as your imagination can go — hook up a JTAG box, build the OS, and get hacking! Get 30% off the Creative Coding Kit with the TRY-LTC-18 coupon code until June 30, 2018!

Taobao breakout boards are a mess part 2

via Dangerous Prototypes

HMC5883L

Last week we struggled with mislabeled and faulty breakout boards from Taobao. Fortunately purchases from Shenzhen sellers usually arrive the next day, so we’ve already got a bunch of replacement boards to test.

HMC5883L/QMC5883 digital compass

Last week our HMC5883L breakout turned out to have a non-compatible QMC5883 chip. We need the genuine part to do a demo so we purchased four more from different suppliers. Each supplier confirmed that the breakout has an original HMC5883L, not the guochan (locally produced) QMC5883.

Of the four boards, only one has a genuine HMC5883L. The only seller with the original part actually offered the option of a guochan version for around 10RMB, or the original for around 40RMB. All the other breakouts came with a QMC5883 and cost around 10-15RMB. There are dozens of listings for this breakout on Taobao for around 10RMB, it’s safe to assume they’re all actually using a QMC5883.

circle

One of the sellers of the QMC5883 boards strenuously argued that the part was real and drew a helpful circle on our photo pointing out the model number. We countered with a photo of the chip markings compared to an original. At this point someone higher in the support chain, probably the boss, confirmed that “everyone” switched to the cheaper Chinese chip a year ago, and that buyers all know this. Now we know too.

SHT21 temperature and pressure sensor

SHT21

First, a correction from last week. We made a pretty basic mistake reading the SHT21 datasheet. The measurement resolution control of the configuration register is split into bits 7 and 0, not 7 and 6. After recognizing this the default value 0x3A is realistic.

Read correctly, bit 6 (0) correctly shows VDD > 2.25volts, the heater is disabled (bit 2=0), and OTP Reload is disabled (bit 1=1). Embarrassing, but an encouraging sign things are looking up.

SHT21

That leaves the issue of the impossibly high and definitely incorrect humidity measurement. We purchased a replacement SHT21 from Youxin, the original vendor, and samples from two other Taobao sellers.

All three breakouts work as expected, but on closer examination the board on the far right is actually an HTU21, not a Sensirion SHT21. HTU21 is a drop in replacement for the SHT21, but much cheaper. An Sensirion original is around 30RMB ($5), while the HTU21 is just 10RMB (~$1.50). The seller marked it as an SHT21 original and charged the market rate for an original (~35RMB). An extraordinarily low price consistently means non-original parts, but unfortunately a reasonable market price isn’t a reliable indicator of genuine parts.

It’s probably not a scam

The confusion probably starts with first line support reps that don’t know what they’re selling. If it says HMC5883, it must be HMC5883, right? Another part is being an informed consumer. If the original goes for 40RMB, the 12RMB version is going to be a substitute. This is obvious now, but the sheer volume of mislabeled listings makes it really hard to get a handle on a reasonable market price.

Taobao offers a huge selection of inexpensive parts, and next day delivery is usually around $1. That’s really amazing! However, getting multiples of everything to ensure at least one is genuine probably costs more than buying from a western-facing supplier like Seeed Studio, SparkFun or Adafruit.