440 lines
26 KiB
HTML
440 lines
26 KiB
HTML
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<!DOCTYPE html>
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<html lang="en">
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<head>
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<title>sensor watch | jack bond-preston</title>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1">
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<link rel="stylesheet" href="../../style/stylesheet.css">
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<link rel="icon" type="image/png" href="data:image/png;base64,iVBORw0KGgo=">
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<style>
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p a, li a {
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font-weight: normal;
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text-decoration: underline;
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}
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p img {
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max-width: 100%;
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display: block;
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}
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body {
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padding: 0;
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margin: 0;
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min-height: 100vh;
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}
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.article {
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padding: 5rem;
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padding-bottom: 1rem;
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}
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.wrapper {
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display: grid;
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grid-template-columns: 30rem auto;
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grid-template-rows: auto;
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gap: 0;
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min-height: 100vh;
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.side {
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background-image: url(images/f91w-strap.svg);
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background-repeat: repeat-y;
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}
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.side > svg {
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width: 30rem;
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position: fixed;
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@media only screen and (max-width: 1200px) {
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.wrapper {
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grid-template-columns: 10rem auto;
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grid-template-rows: auto;
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.side > svg {
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width: 10rem;
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padding-left: 1rem;
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padding-right: 1rem;
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padding-top: 1rem;
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font-size: 1rem;
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}
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@media only screen and (max-width: 600px) {
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.side {
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display: none;
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grid-template-columns: auto;
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grid-template-rows: auto;
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.article {
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padding: 10px;
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font-size: 0.8rem;
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}
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}
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</style>
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</head>
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<body>
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<div class="content">
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<div class="article">
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<!-- article body { -->
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<h1 id="title"><a href=".">sensor watch</a></h1>
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<h2 id="premable"><a href="#preamble">preamble</a></h2>
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<p>
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some time back I was browsing <a href="https://www.crowdsupply.com/">Crowd Supply</a> when I came
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across <a href="https://www.crowdsupply.com/oddly-specific-objects/sensor-watch">the Sensor
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Watch project</a> by Joey Castillo. I had wanted some kind of "hackable" watch for a while, and had
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looked at things like <a href="https://www.crowdsupply.com/sqfmi/watchy">Watchy</a>, but this
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project hit the sweet spot for me. I love my existing F91-W, and this project was a good
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combination of open source with community software support. one key feature that was important to
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me is battery life - the Sensor Watch battery life in an average usage scenario is so long that
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<a href="https://twitter.com/josecastillo/status/1590066358351298560">Joey's is still going
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strong</a>!
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</p>
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<p>
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I was excited to pick one up and start messing around with it, but the first issue I came across
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was availability - the delivery date for Crowd Supply orders was summer 2023 (I think they ended up
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being delivered sooner than this, not sure). on top of this, shipping and import fees made it
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pretty prohibitively expensive. I've always found this to be an issue with Crowd Supply as someone
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based in the UK, even some things designed in the UK are very expensive from Crowd Supply as they
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are assembled in/shipped from the US. so I decided to build one myself!
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</p>
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<h2 id="component-acquisition"><a href="#component-acquisition">component acquisition</a></h2>
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<p>
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the first challenge was acquiring all the necessary parts to actually build one. I downloaded
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<a href="https://github.com/joeycastillo/Sensor-Watch/tree/main/PCB/Main%20Boards">the PCB files</a>
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and generated a <a href="https://en.wikipedia.org/wiki/Bill_of_materials">BOM</a> to figure
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out exactly what I needed to acquire. I'm sure in ordinary times this would be easy enough, but the
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current state of some electronics/silicon supply chains had other things to say. some parts are of
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course still easy to come across, e.g. 10pF 0402 caps and 10k 0603 resistors; most of the
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components of the Sensor Watch are this kind of commonplace part. what quickly became clear from
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some scouring of the internet was that my main problem was going to be two parts: the
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<a href="https://www.microchip.com/en-us/product/ATSAML22J18A">ATSAML22J18A-MUT</a> (the processor
|
||
|
|
driving the Sensor Watch), and the <a href="https://www.hirose.com/en/product/series/FH19C__FH19SC">
|
||
|
|
FH19C-9S-0.5SH(10)</a> (the connector used to attach the extra sensor boards).
|
||
|
|
</p>
|
||
|
|
<h3>ATSAML22J18A-MUT</h3>
|
||
|
|
<p>
|
||
|
|
the former of these was a fairly well discussed shortage that had been ongoing for a while. it was
|
||
|
|
<a href="https://www.crowdsupply.com/oddly-specific-objects/sensor-watch/updates/blue-boards-shipping-check-your-address-green-boards-delayed-and-other-news-of-the-watch">
|
||
|
|
the driving force of the Sensor Watch Crowd Supply delay</a>. I spent quite a lot of time searching
|
||
|
|
around the internet, looking at various sites on the English-speaking and Chinese-speaking web.
|
||
|
|
sadly this part was clearly in very short supply, and prices could get pretty insane from vendors
|
||
|
|
that did have some stock. I received quotes for unit prices that include the following (USD/GBP):
|
||
|
|
$79.35, $6.56, $13.61, $6.83 (MOQ 4000), £6.45. I guess some people are desperate enough to pay
|
||
|
|
$79.35 :(. I spent so long looking for them that they ended up randomly coming back in stock on
|
||
|
|
<a href="https://www.microchipdirect.com/">MicrochipDirect</a>. as of the time of writing this
|
||
|
|
article,
|
||
|
|
<a href="https://www.microchipdirect.com/product/ATSAML22J18A-MUT">they are again out of stock</a>.
|
||
|
|
the unit price I bought them for was £3.92, shipping and handling was ~£12.
|
||
|
|
</p>
|
||
|
|
<h3>FH19C-9S-0.5SH(10)</h3>
|
||
|
|
<p>
|
||
|
|
this part was out of stock everywhere I initially looked (the usual contenders for parts). I
|
||
|
|
searched around in a similar manner as the ATSAML22J18A-MUT, and found some similarly wild pricing.
|
||
|
|
I ended up purchasing a small quantity at a unit price of £0.44 from a website called
|
||
|
|
<a href="http://archive.today/2022.11.13-230943/https://www.dacikeys.net/">dacikeys</a>. yes, the
|
||
|
|
site is actually called this. yes, the unit price is cheaper than digikey and mouser. yes, I
|
||
|
|
actually received all of my order, consisting of working parts. I was definitely shocked that this
|
||
|
|
happened, but sometimes bravery pays off I guess. I still can't endorse this shop.
|
||
|
|
</p>
|
||
|
|
<h3>PCB and stencil</h3>
|
||
|
|
<p>
|
||
|
|
for the PCB I opted to go with <a href="https://jlcpcb.com/">JLCPCB</a>. I simply uploaded the
|
||
|
|
relevant gerbers, and adjusted the necessary settings. notably,
|
||
|
|
<a href="https://github.com/joeycastillo/Sensor-Watch/issues/14#issuecomment-922974276"></a>the
|
||
|
|
thickness should be 0.6mm</a> - this does narrow the choice of manufacturer (for example, OSH Park
|
||
|
|
doesn't go this thin). I haven't yet ordered any sensor board PCBs, but
|
||
|
|
<a href="https://www.pcbway.com/">PCBWay</a> seems to be <i>the</i> option there. The PCB turned
|
||
|
|
out great, although the silkscreen is a little hard to read at this size due to lack of sharpness:
|
||
|
|
<img src="images/pcb.jpg" />
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<h2 id="assembly"><a href="#assembly">assembly</a></h2>
|
||
|
|
<p>
|
||
|
|
I decided to assemble myself. partially because the logistics of paying for assembly when I had to
|
||
|
|
source parts from many different providers seemed like a headache, partially because I thought it
|
||
|
|
would be a fun challenge and learning experience!
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
a few things were necessary to solder the components to this PCB. I'm sure someone talented could
|
||
|
|
hand solder this with an iron, but I can name a lot of things I'd rather do than try to do that
|
||
|
|
(especially the <a href="https://en.wikipedia.org/wiki/Flat_no-leads_package">QFN</a> SAML) - and
|
||
|
|
that list includes unpleasant things. I opted to go with
|
||
|
|
<a href="http://www.flyelectric.org.uk/hot_plate.htm">hotplate soldering</a>, which is a cheaper
|
||
|
|
way to access the ease of reflow soldering. for a PCB like the Sensor Watch, where almost all the
|
||
|
|
components are on one side, it's ideal. the hotplate I have is the ever-popular
|
||
|
|
<a href="https://www.miniware.com.cn/product/mhp30-mini-hot-plate-preheater/">MHP30</a>, which I
|
||
|
|
run <a href="https://github.com/Ralim/IronOS">IronOS</a> on. I highly recommend it, it's great! my
|
||
|
|
soldering iron is the iconic
|
||
|
|
<a href="https://pine64.com/product/pinecil-smart-mini-portable-soldering-iron/">Pinecil</a> (not
|
||
|
|
the <a href="https://www.pine64.org/2022/07/28/july-update-a-pinecil-evolved/">fancy new V2</a>
|
||
|
|
though :[) which also runs IronOS. nice!
|
||
|
|
</p>
|
||
|
|
<h3>process</h3>
|
||
|
|
<p>
|
||
|
|
the assembly process is as follows:
|
||
|
|
<ul>
|
||
|
|
<li>
|
||
|
|
apply solder paste to the PCB with the stencil. make sure the stencil is really flush and just
|
||
|
|
kind of squeegee it on with a plastic card. I used tape to hold it in place. then carefully
|
||
|
|
removed the stencil, avoiding smudging the paste in doing so.
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
place components on the PCB. this was by far the most painful part of the whole process. a
|
||
|
|
steady hand is not something I was blessed with, and some of these parts are really small. I used a
|
||
|
|
microscope from Amazon for this, the ample manouverable lighting was a big help. a lot of time and
|
||
|
|
patience is required, but it's very first time doable with no prior experience! simply go through
|
||
|
|
the parts one by one, or by area of the board - whatever you prefer. then pick up the respective
|
||
|
|
part with some fine tweezers, and slowly put in place on the solder paste. thankfully, the paste
|
||
|
|
will lightly stick the component in place once you've done this (it is not knock-proof though!).
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
carefully (really!) place the PCB onto the hotplate and heat up. keep on until everything seems
|
||
|
|
to be melted, and the components have hopefully been pulled into place. that's the top side done!
|
||
|
|
let it cool down, then move on to the bottom.
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
time for some hand soldering. the button is pretty small, and very fiddly to do. I found you don't
|
||
|
|
need too much precision, but you have to be really careful with your iron as the plastic button
|
||
|
|
will melt if you touch it. once that's in place, it's just a matter of
|
||
|
|
<a href="https://youtu.be/Zr0pKeC2VFU?t=185">removing the buzzer connector from your old PCB and
|
||
|
|
soldering it onto the back of the Sensor Watch PCB.</a> this will feel blissfully easy after the
|
||
|
|
button! you also have to place the battery clip, but no soldering needed here :).
|
||
|
|
</li>
|
||
|
|
</ul>
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
one area I found particularly difficult was the area with the oscillator crystal and the two 0402
|
||
|
|
capacitors, C7 and C8. things are a bit cramped here, so extra care was needed:
|
||
|
|
<img src="images/c7c8.jpg" />
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<h2 id="software"><a href="#software">software</a></h2>
|
||
|
|
<p>
|
||
|
|
at this point the watch was assembled with all components in place. did it work? at this stage, no
|
||
|
|
idea. hopefully yes, and I could progress to the more familiar world of embedded software.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<h3>bootloader</h3>
|
||
|
|
<p>
|
||
|
|
the next necessary step is to flash the bootloader, so that we can put the firmware in place.
|
||
|
|
unfortunately this requires a little more real-world action. we need to access the SWD points on
|
||
|
|
the board to write the bootloader. ideally you could do this with some kind of
|
||
|
|
<a href="https://en.wikipedia.org/wiki/Pogo_pin">pogo pin</a> jig - and if you were doing any
|
||
|
|
number exceeding about 5 I'm sure this would be worth the time. however, I decided to just solder
|
||
|
|
some jump wires (stripped on one end, solid tip female on the other) to the points on the board.
|
||
|
|
they're all close, but it's easy enough to do (albeit ugly). then I connected these to my
|
||
|
|
<a href="https://www.adafruit.com/product/1501">Adafruit Trinket M0</a> (PyRuler would also work).
|
||
|
|
the pin mapping is as follows: SWD=0, SWC=1, RST=3, V+=3V, GND=GND.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<p>
|
||
|
|
I used the
|
||
|
|
<a href="https://github.com/joeycastillo/Sensor-Watch/blob/main/utils/flash_watch_pyruler/flash_watch_pyruler.ino">
|
||
|
|
flasher from the sensor watch repo to flash the bootloader</a>. note that you could build the
|
||
|
|
bootloader yourself first and put the generated binary into bootloader.h - the source is located
|
||
|
|
<a href="https://github.com/joeycastillo/uf2-samdx1">here</a>. personally, I just used the prebuilt
|
||
|
|
version from the repo. I had to change part of the Adafruit DAP library and add the SAM L22 DID to
|
||
|
|
get this to work,
|
||
|
|
<a href="https://github.com/joeycastillo/Sensor-Watch/issues/83#issuecomment-1229353899">I provided
|
||
|
|
the diff of this change</a> in a Sensor Watch GitHub issue (I just now am remembering I promised to
|
||
|
|
upstream this, oops!). mercifully, I got the red blinky LED, and all was good! I unsoldered the
|
||
|
|
wires from the board, and tried to clean up most of the solder blob to keep the board fairly flat.
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<h3>movement</h3>
|
||
|
|
<p>
|
||
|
|
now the bootloader is in place, the main firmware can be installed!
|
||
|
|
<a href="https://www.sensorwatch.net/docs/movement/">the community firmware, Movement</a> is great,
|
||
|
|
so this is what I installed. there are a bunch of different useful faces available, and more
|
||
|
|
functionality is always being added.
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
flashing firmware was easy: I plugged the PCB into the end of a USB Micro B cable (plugged on the
|
||
|
|
other end into my computer) and double tapped the reset button (I find this has to be done quite
|
||
|
|
quickly, using my fingernail was the trick to doing this reliably on such a small button). done
|
||
|
|
successfully, the LED on the board pulses and a new drive labelled "WATCHBOOT" appears on the
|
||
|
|
computer. now a built UF2 firmware file can just be dragged onto the device to flash, thanks to the
|
||
|
|
bootloader flashed earlier. for the initial test, I just used a
|
||
|
|
<a href="https://www.sensorwatch.net/docs/firmware/prebuilt/">prebuilt image</a> to check
|
||
|
|
everything was working. I flashed this, and the LED pulsed and turned off, signalling success.
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
from here I just assembled the watch with the Sensor Watch PCB, and it worked! I verified LED and
|
||
|
|
buzzer function by playing around with various functionality. success!
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<h2 id="developing-movement"><a href="#developing-movement">developing on movement</a></h2>
|
||
|
|
<p>
|
||
|
|
one face I found particularly cool was the <a href="https://github.com/joeycastillo/Sensor-Watch/blob/main/movement/watch_faces/complication/totp_face.c">
|
||
|
|
TOTP face</a>. I use <a href="https://en.wikipedia.org/wiki/Time-based_one-time_password">TOTP</a>
|
||
|
|
<a href="https://en.wikipedia.org/wiki/Multi-factor_authentication">2FA</a> on various accounts, so
|
||
|
|
having access to the codes on my wrist at all times was really appealing. at the time, the TOTP
|
||
|
|
face only supported one key - so I decided to improve it.
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
thankfully, Sensor Watch has an emulator for development. without this, development would be pretty
|
||
|
|
tiresome with the flashing and reassembling of the watch getting tiring if you needed to iterate on
|
||
|
|
some code and test it on the watch. the emulator runs inside the browser and uses
|
||
|
|
<a href="https://en.wikipedia.org/wiki/Emscripten">Emscripten</a>.
|
||
|
|
<a href="https://github.com/joeycastillo/Sensor-Watch#using-the-movement-framework">some minimal
|
||
|
|
instructions on how to build this is available on the README</a>. this allowed me to extend the
|
||
|
|
TOTP face easily and allow for multiple keys.
|
||
|
|
<a href="https://github.com/joeycastillo/Sensor-Watch/pull/84">my PR was merged</a>, and the
|
||
|
|
functionality is now available for anyone to use. the keys are added at compile time, so they are
|
||
|
|
baked into the firmware on flashing. for my purposes this is fine, as I never really change them.
|
||
|
|
however, with the recent addition of a
|
||
|
|
<a href="https://os.mbed.com/blog/entry/littlefs-high-integrity-embedded-fs/">LittleFS</a>
|
||
|
|
filesystem, the community have added <a href="https://github.com/joeycastillo/Sensor-Watch/blob/main/movement/watch_faces/complication/totp_face_lfs.c">
|
||
|
|
a version of the face which stores the keys on the filesystem</a>. awesome!
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
some more details on using Sensor Watch for TOTP is available
|
||
|
|
<a href="https://blog.singleton.io/posts/2022-10-17-otp-on-wrist/">on this blog post</a>
|
||
|
|
(<a href="https://news.ycombinator.com/item?id=33243434">HN discussion, if you dare</a>). it's even
|
||
|
|
running my code :)!
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<h2 id="epilogue"><a href="#epilogue">epilogue</a></h2>
|
||
|
|
<p>
|
||
|
|
<img src="images/watch1.jpg" />
|
||
|
|
<img src="images/watch2.jpg" />
|
||
|
|
<img src="images/wrist.jpg" />
|
||
|
|
</p>
|
||
|
|
<p>
|
||
|
|
some summary thoughts:
|
||
|
|
<ul>
|
||
|
|
<li>
|
||
|
|
shoutout to Joey Castillo. for creating the Sensor Watch as a beautifully open source project (the
|
||
|
|
fact I could independently make my own is what it's all about!). for being
|
||
|
|
<a href="https://github.com/joeycastillo/Sensor-Watch/issues/83">so helpful and kind</a> when I
|
||
|
|
asked for help. for having such a positive attitude towards those in the community who are using
|
||
|
|
Sensor Watch to learn about all kinds of things (seriously, check out the
|
||
|
|
<a href="https://discord.gg/NtMVTBNca7">Oddly Specific Objects Discord</a> to see how much this guy
|
||
|
|
is giving to the community).
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
sometimes it's worth just trying things that are difficult. this is my first time successfully
|
||
|
|
doing and small-scale soldering of this kind, and it worked out great with some patience. having
|
||
|
|
the motivation from making something I thought was really cool was an important factor here I think.
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
if you have a Sensor Watch (or are planning to!) please go ahead and <a href="https://github.com/joeycastillo/Sensor-Watch">
|
||
|
|
contribute to movement</a> if you have a cool idea. I'm sure some reviews would be helpful to spot
|
||
|
|
any issues on existing PRs before a maintainer gets to them to save some time.
|
||
|
|
</li>
|
||
|
|
<li>
|
||
|
|
the one issue I've had with using my Sensor Watch for TOTP is clock accuracy. the clock drifts over
|
||
|
|
time, so I have to set the time once or twice a week to keep it nice and accurate for the TOTP
|
||
|
|
functionality to be nice to use. but a community member is working on this, and it's going to get a
|
||
|
|
lot better. check out the Discord channel to see some seriously cool engineering going into this
|
||
|
|
calibration effort.
|
||
|
|
</li>
|
||
|
|
</ul>
|
||
|
|
</p>
|
||
|
|
<br />
|
||
|
|
<br />
|
||
|
|
<p>
|
||
|
|
<a href="mailto:jackbondpreston@outlook.com">email me</a> to have a conversation
|
||
|
|
</p>
|
||
|
|
|
||
|
|
<!-- } -->
|
||
|
|
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</div>
|
||
|
|
</body>
|
||
|
|
|
||
|
|
</html>
|