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micro:bit wear:it Development Kit - Review

Scoring

Product Performed to Expectations: 6
Specifications were sufficient to design with: 10
Demo Software was of good quality: 10
Product was easy to use: 10
Support materials were available: 10
The price to performance ratio was good: 10
TotalScore: 56 / 60
  • RoadTest: micro:bit wear:it Development Kit
  • Buy Now
  • Evaluation Type: Independent Products
  • Was everything in the box required?: Yes
  • Comparable Products/Other parts you considered: To some extent, Arduinos.
  • What were the biggest problems encountered?: * Didn't work out of the box: the metallic tabs that should supply power from the case to the micro:bit didn't make contact. * The on-off switch is very hard to use when the case is closed and the micro:bit and batteries are inside. * Sometimes it smelled like a burnt circuit, and batteries got really hot, but only when using it inside of the wear:it (was short-circuiting I think). * micro:bit behaves differently when connected by USB than on batteries (real bummer for my project). I provide more detail on each of these in the body of the review.

  • Detailed Review:

    Micro:bit wear:it, what is it?

     

    The micro:bit is an integrated computing platform that is very easy to program, intended for kids to get interested into STEM. It is pretty much like an Arduino, but unlike it, it comes with sensors and actuators directly integrated into the board: a 5x5 LED matrix for screen, 2 button switches, accelerometer, thermometer, light sensors, and more. If you wanted to display the message "Hello world" in an Arduino you'd need to wire a screen first and write some code for scrolling the text and import a 3rd-party library, but with micro:bit it's as simple as this:

    from microbit import *

    display.scroll("Hello, World!")

    But well, this is not a review of the micro:bit but of the wear:it accessories:

    The wear:it accessories are basically an enclosure and wristband intended to create wearable applications with the micro:bit. It comes with a compartment for the batteries so you don't need to use any wires. It also has holes perfectly located so you can press the buttons while wearing it. At first glance I liked the idea (I always think about how I'm going to power the device, and here that's solved).

     

    I received the micro:bit and wear:it together in exchange for a honest review, so here it is.

     

    In this review:

    • The good
    • The bad
    • Miss Morita's costume project

     

    By the way, say hello to Morita, she used the wear:it as soon as it arrived. Later, I really integrated the wear:it into the costume for maximum dog comfortability:.

     

     

    You'll see programming the micro:bit is really simple, it didn't take long to do that beating heart (download the source code here).

     

    Review wear:it

     

    The good

     

    The micro:bit has several buttons, IO ports and sensors, and when they designed the wear:it they ensured we could use them all without taking the enclosure apart.

    Look at these pictures:

     

    {gallery} The Good Parts

    Reset Button: I liked that the reset button lined perfectly with this hole in the enclosure

    IO Ports: And I liked as well that they provided a removable bottom so we could access the IO ports without having to take it off your wrist

    Wrist bands: It also comes with two wrist bands, one more colorful than the other

    Hangy Thingy: It also comes with this retainer.

    More of those: I don't know for what I'd use so many retainer, but there they are.

     

    There is also a lot of good to talk about the micro:bit itself, but I'm leaving it for the end.

     

     

    The bad

     

    Misaligned Battery Contacts

     

    The wear:it didn't work out-of-the-box . I assembled it and then, nothing happened, as if no power was getting fed to the board.

     

    Upon closer inspection, I noticed one of the 2 sets of tabs used to power the board was misaligned:

    So the tabs that were higher were making correct contact, but the ones that were lower where missing it by a little. This is where the battery contacts should be touching:

    So, to fix this, I took a screw and moved the contact a bit up, just to the position where it would make contact with the board. Success! that's all the wear:it needed to be powered.

     

     

    Scratched Battery Contacts

     

    Maybe I'm being too picky about this one, but do you notice how, in the previous image, the bottom contact is all scratched? I'd prefer the board to not suffer damage from the wear:it, I wonder if after some months of use the battery tab will lift the pad and permanently damage the micro:bit.

     

     

    Hard to use On/Off Switch

     

    After using it for a while, it came the time to turn the micro:bit off and save some battery power. This is accomplished by turning a small lever in the enclosure:

    When that lever is turned in the outside, this small plastic piece should move in between the battery and the metallic contact:

    Thus breaking the current flow:

    The issue? when the enclosure is closed and the micro:bit is inside, it's really hard to generate enough torque with a lever that small to displace the battery and break the current flow. For real, I couldn't do it without risking a nail, so I resorted to just opening the enclosure and removing the micro:bit whenever I wanted it powered off.

     

     

    Burnt smell when attaching the micro:bit to the wear:it

     

    After some days with this product, I put the micro:bit in the wear:it and I could feel the smell of burnt solder. I removed the micro:bit quickly, waited for a moment, and put it inside again and the issue didn't repeat. I kept removing it and putting it in and some times I could reproduce the issue, some others I couldn't. But I noticed every time it happened the transparent lid had been tightly secured in place, just putting the micro:bit above the contacts or putting the lid without securing it doesn't produce any issues. I don't know what causes the short-circuit (I think it's a short-circuit as the AAA batteries get really hot when the problem occurs), but it's something related to the wear:it as connecting the micro:bit via USB to the PC doesn't produce any smell. I tried checking with my finger if one of the ICs was getting hot but couldn't find any.

     

    I have two hypotheses as for what causes the issue:

    1. I see the micro:bit has some contacts close to the contacts the wear:it uses to power the micro:bit. So, it's possible the wear:it was short:circuiting those other contacts.
    2. The battery's exterior may be pushing on the micro:bit's circuitry, causing one the IC to short-circuit internally or just bending the contacts enough to short-circuit them.

     

     

    The micro:bit behaves differently when connected to USB

     

    This one was a real bummer for my project: I connected the micro:bit to a different board, the AudioFX from Adafruit, and my objective was to send a logical 1 or 0 from the micro:bit to the AudioFX to start/stop the music. Sounds simple, just connect the GNDs together, and then another cable from Pin 0 on the micro:bit to the correct pin on the AudioFX.

     

    Well, this strategy worked perfectly but only when the micro:bit was connected through USB to a computer (or portable power bank), but it didn't work when powering it from AAA batteries inside the wear:it. I thought maybe the batteries didn't provide enough current, but in this AudioFX board it's actually setting the pin to GND what turns the music ON, so that didn't seem like the cause. But anyway, I connected both cables to the GND on the micro:bit side, and the music did start, so it didn't look like something about not having enough current but something related to Pin 0 in the micro:bit. I tried with Pins 1 and 2 too, with the same luck.

     

    I don't know the reason of this weird behaviour as I don't have an oscilloscope to debug it (and the multimeter didn't help). Though reading on these docs, I found that depending on which power source one uses there are some hardware interfaces that are/aren't powered, like the KL26.

     

    Oh and the reason I mention it's a bummer is because even a power bank is not an appropriate solution, as they turn off automatically after some seconds if they don't detect a considerable amount of current being drawn. So it will only power the micro:bit for a moment. I tried both batteries and power bank at the same time, but as soon as the power bank turned off, the AudioFX board stopped receiving the GND signal.

     

    Finally: Miss Morita's costume

     

    I bought an Audio FX Board from Adafruit in order to play music along with my dog's costume: Hermione Granger from Harry Potter, and I'd like to play Harry Potter's theme when she's posing for a picture, automagically, i.e. I don't want to press a button to make the music play, I want the music to play as soon as Morita is posing. To accomplish this I'm planning to sew a pocket in her cloak and put the micro:bit+wear:it in there, in a exact orientation, it will then detect if she's standing or sitting by using the accelerometer.get_y() function like this:

     

    I found those constants -by using micro:bit's REPL: rotating the board and seeing how the X, Y and Z readings of the accelerometer.get_y() changed. Similar values are used in the code to decide if the dog was standing or sitting.

     

    These are the components of the project: a micro:bit inside of its wear:it case, an AudioFx board, batteries for the AudioFx board, speakers, and two pockets we'll sew to the interior of the cloak and where we'll put the components:

    micro:bit and AudioFx board

     

    So, we sewed pockets on the inside of Morita's cloak, and put on one side the wear:it + micro:bit  and at the other side, the AudioFX board with its batteries and speakers. The pockets are at opposite sides to balance the weight, so the cloak doesn't fall to one side.

     

    The cables that connect both board are hidden inside the cloak, there are two fabrics, the exterior is black and the interior is red, the cables are in between them, and go through holes concealed behind the pockets we later sown:

    cloak concealing cables

    The micro:bit is connected by using alligator clips, and because keeping it in an exact orientation is very important for this project, the pocket size is just enough to put the wear:it inside and not allowing it to move:

    micro:bit inside its pocket

    This is how it works, tilting the pocket to the position it would have when the dog is sitting will send the ON signal to the AudioFx board and play the music, tilting it to the position it would have if the dog were standing will send the OFF signal:

     

     

     

    Thanks for checking out this review, the code for the project can be found in GitHub.


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