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<figure>
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<img src="https://f000.backblazeb2.com/file/bsag-blog-imgs/handwired%5Fcorne%5Fin%5Facrylic%5Fcase.jpeg"/>
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</figure>
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<p>It seems that building keyboards is addictive. After my <a href="https://www.rousette.org.uk/archives/building-a-corne-low-profile-keyboard/">first attempt</a>, I
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made another, this time a version with LED lighting. At least, that was the
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plan. While the soldering for the keyboard itself went smoothly, soldering the LEDs
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(SK6812MINI 3228 LEDs) was enormously frustrating. These LEDs have tiny contact pads
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on the back of the unit, so to solder them into the openings in the PCB so that
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they shine through the switches, you are supposed to create solder bridges from
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the back of the LED to the PCB. Since the LEDs melt at temperatures quite close
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to those needed to melt lead-free solder this — to put it mildly — is quite
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a challenge. On one half of the keyboard, I got some of the underglow lights
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working, but none of the per-key lights. On the other half, none of the lights
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worked. I finished the keyboard and was pleased with the low-profile build, but
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the situation with the lights quietly nagged at me. Through a combination of
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curiosity and stubbornness, I felt compelled to have another go, and this
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third Corne keyboard is the result.</p>
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<h3 id="the-layout">The layout</h3>
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<p>It is probably obvious by now (given that this is my third) that I love
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the key layout and form factor of this keyboard. I love the fact that every key
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is only one unit away when my fingers (and thumbs) are in their ‘home’
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positions. The layout I have created for numbers, navigation and symbols makes it
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extremely easy to type everything without stretching or searching. I went the
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slightly unconventional route of placing the numbers in two rows on the left
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half of the keyboard (1-5 on the top row and 6-0 on the home row). I have been
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able to touch type for a while, but have never been able to accurately touch
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type numbers until now. I could go on, but the main point is that I wanted to
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stick with everything I had used for my previous builds (layout, Kailh Choc blue
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key switches, and so on) but use SK6812MINI-E 3228 LEDs instead of the
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frustrating SK6812MINIs.</p>
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<p>The MINI-Es are very similar in size, and have the same capabilities, but
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instead of the fragile pads on the back of the LED, they have little copper legs
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which stick out either side. When you drop the LED into the PCB cut-out, the
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legs stop it falling through the hole, and sit flush with the pads on the back,
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so they are <em>much</em> easier to solder. The problem, however, is that despite the
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similar part code, MINI-Es have a different pin-out and so are wired up
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completely differently from the MINIs. This means that you can’t just substitute
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them unless the PCB has been designed especially for them. In <a href="https://github.com/foostan/crkbd/blob/main/corne-chocolate/doc/buildguide%5Fen.md">Version 3</a> of the
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Corne PCB, the version for MX key switches is designed for the MINI-E, but the
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Choc version uses the MINI LEDs. I did toy with the idea of learning how to
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modify a PCB design using Kicad, but that seemed like too much of a leap in
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terms of my knowledge. I mean, I’ve only just learned how to use a multi-meter
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to test continuity, so my electronics knowledge is not exactly extensive!
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Instead, I decided to hand-wire the keyboard so that I could take into
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account the different pin-out of the LEDs.</p>
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<h3 id="hand-wiring">Hand-wiring</h3>
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<p>Hand-wiring a keyboard isn’t that hard. There are a number of detailed guides
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available (this one by <a href="https://www.masterzen.fr/2018/12/16/handwired-keyboard-build-log-part-1/">masterzen</a> is very clear), and with a small keyboard like
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the Corne, you don’t have to do too much work. However, I wasn’t sure how neat I
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would be able to keep the LED wiring without a PCB, and how I would keep them in
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place, as well as anchoring the controller and TRRS jacks. While pondering this,
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I came across the <a href="https://github.com/swanmatch/MxLEDBitPCB">MxLEDBit single key PCBs</a>. These clever little things provide
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support for a single key switch (versions for MX and Choc are available),
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and provide breakout pads for wiring up the rows and columns, as well as
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data in and out and power/ground connections for LEDs. There are also dedicated pads
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for surface mounting diodes on each PCB. There are several similar versions out
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there, but the benefit of the MxLEDBit is that it is compatible with the
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MINI-Es. There’s also a board that houses the ProMicro compatible controller
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together with the reset switch and TRRS jack.</p>
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<p>I really like these little PCBs, but there’s a reason people use standard PCBs:
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wiring everything up yourself takes so much longer, and the end result is
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inevitably more bulky (even if you carefully route the wiring) than a standard
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PCB would be. Once I had resigned myself to this being a multi-weekend project,
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I found it quite a mindful process. My first task (which turned out to be the
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quickest part of the project) was to solder a diode and LED to each PCB. I
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hadn’t used surface-mount diodes before, but apart from the challenge of
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actually <em>seeing</em> the things properly to check polarity, they weren’t too hard to
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solder. The MINI-E LEDs were a delight. I couldn’t be sure until I
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finished the project but — spoiler alert — it turned out that the soldering
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of each LED worked fine first time. I would never go back to trying to use the
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MINIs as the MINI-Es are so much less trouble. Once each of the PCBs had the
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components fitted, I separated them into individual units (they come as a 5x5
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grid) and started on the assembly.</p>
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<p>I re-used quite a few of the components from my first keyboard build, but I
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bought an acrylic sandwich case to build the keyboard around, as it enabled me
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to adjust the height by using more or less of the acrylic layers. Since I didn’t
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know quite how might height I would need to accommodate the wiring, it was
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useful to have this flexibility. The switch plate was a bit thicker than is
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ideal (3 mm). If I had been using hot-swap sockets for the key switches, I don’t
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think they would have held in place well, but with the MxLEDBit PCBs pushed tight
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against the underside of the acrylic, there was just enough of the switch pin
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protruding for me to solder them on. Before soldering the switches in, I created
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all the row and column wire connections and tested for continuity with a
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multi-meter.</p>
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<h3 id="wiring-the-matrix-and-leds">Wiring the matrix and LEDs</h3>
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<p>I used solid core 22 AWG wire for the rows and columns, and then stranded core
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22 AWG wire to connect the rows and columns to the controller, as its flexibility
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enabled me to move the wire around to provide room to solder the LED connections
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later. I cut a piece of the solid core wire, stripped one end, bent the stripped
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portion into a right angle and then figured out the length needed to the next
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connection before trimming, stripping the wire and bending it. Each connecting
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piece was therefore like a staple, and just long enough to reach from one pad to
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the next. When I started, I had to be careful not to dislodge the key switches
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(remember that I had not yet soldered them in), but as I soldered more of the
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matrix with the solid wires, the whole thing held together better. Once I was
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happy with the continuity of all the wires, I soldered the controller on to the
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controller PCB, connected up the controller to the rows and columns and tested
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each switch footprint with tweezers using the <a href="https://caniusevia.com">Via keyboard tester</a>. I had to
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re-flow the solder one connection, but otherwise it all worked perfectly!</p>
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<p>After soldering the key switches and testing again, I moved to the LEDs. I had
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wired the rows and columns of the keyboard in exactly the same way as the
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standard Corne to make life easier as I did not have to touch those aspects in
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the firmware. I could not really do the same for the LEDs, as I was not using
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underglow LEDs at all (so I had fewer units), and it also made more sense to
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wire them in a different order because of the location of the pads. I wasn’t
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absolutely sure it was going to work, but after looking at the firmware, I was
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fairly confident that I could specify a different number and layout order of
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LEDs. Each PCB has a <code>DIN</code> and <code>DO</code> pad for data in and data out respectively. I
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started by connecting the LED pin on the controller with the <code>DIN</code> pad of the top
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row key nearest to the controller, then worked my way along the row, down to the
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next row, back towards the controller, and so on, connecting the <code>DO</code> of one key
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with the <code>DIN</code> of the next.</p>
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<figure>
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<img src="https://f000.backblazeb2.com/file/bsag-blog-imgs/the%5Fpretty%5Fguts.jpeg"/>
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</figure>
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<p>By this time, the board was fairly congested with wire, and I still had to
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connect each of the keys to 5V power and ground. I decided to use very fine
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magnet wire for this job to save space. This is enamelled to provide insulation,
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but if you dip the tip in hot solder, the enamel burns off and tins the wire in
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one go. The wire is 0.1 mm diameter (so literally as thick as a human hair), and
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was fairly challenging to see, let alone solder. It was so fine that it blew
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about in the draft from my ventilation fan. I had to manipulate it with my
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fingers rather than tweezers, as I had read that tweezers can scratch the enamel
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coating, leading to shorts. I think this was the part that I found the most
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difficult, but I went slowly, testing as I went with the multimeter to make sure
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that I was creating proper electrical connections.</p>
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<p>Eventually, I had one side of the keyboard completely connected, and held my
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breath as I plugged in the USB cable. Initially, only the first few LEDs lit up,
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and were flickering different colours. I found that the connection from the
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controller to the first key had a bit of a cold solder, and re-flowing that joint
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made all the LEDs light up properly — celebration time!</p>
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<p>With the knowledge that my wiring actually worked, the second half went a bit
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quicker. I cut and placed the wire for each row and column before soldering in
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one go, which was more efficient. I was also able to organise the wires from the
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controller in a more compact way for the second half, learning from the
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experience with the first. This time, the LED wiring worked perfectly first
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time.</p>
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<h3 id="the-case">The case</h3>
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<p>The final task was to assemble the acrylic case. It came with M2 screws and
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standoffs, but I bought some nicer hex socket screws and some different lengths
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of standoffs so that I could organise the layers in the order I wanted. I ended
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up using all the layers to give myself enough space for the wiring, but the end
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product still feels very low profile compared to a standard keyboard. The only
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thing I haven’t solved is anchoring the controller PCB to the case. It has four
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holes to fix it to the case with standoffs or screws, but the acrylic case was
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not designed for it and does not have screw holes. I reckoned that my chances of
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drilling acrylic without cracking it were basically nil. I had thought that I
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might be able to use blobs of <a href="https://sugru.com/what-is-sugru">Sugru</a> to attach the boards to the base of the
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case, but it turns out that the only thing that Sugru <em>doesn’t</em> stick to is
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acrylic. For now the boards are just wedged into the case and I have to be very
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careful when attaching the TRRS or USB cable. Since this board is going to live
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on my desk at home<sup id="fnref:1"><a href="#fn:1" class="footnote-ref" role="doc-noteref">1</a></sup>, that’s not too much of a problem. I may
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eventually be able to figure out a way of securing it a bit more solidly though.
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I do like the way that the coloured light shines out through the sides and base
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of the case. The transparent bottom also means that I can admire my hand-wiring
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when I feel like it too!</p>
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<h3 id="bonus-extra-custom-cables">Bonus extra - custom cables</h3>
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<p>There was one other project that I had half-completed. Some way through building
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the other keyboards, I had bought a custom USB cable kit and some angled TRRS
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connectors with the idea of building custom cables to go with my new keyboard.
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These have paracord sleeves with an extra Techflex sleeve on top for durability
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and extra fanciness. I had already made the USB-C cable without too much
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trouble. The heatshrink tubing application could have been a bit neater, but
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otherwise it wasn’t too difficult and works well. I like having a cable that is
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exactly the right length for my set up so that I don’t have untidy loose wire to
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coil up.</p>
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<figure>
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<img src="https://f000.backblazeb2.com/file/bsag-blog-imgs/custom%5FTRRS.jpeg"/>
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</figure>
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<p>The TRRS was another matter entirely. In the past, I have looked at the prices
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charged by companies making custom USB and TRRS cables and thought that they
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were quite expensive. Now I think that they don’t charge nearly enough money,
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particularly for TRRS cables. Even soldering with magnet wire is easier than
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trying to get those tiny wires into the right spots, avoiding melting the
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insulation, and not getting any shorts. I tried twice and failed completely, but
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decided after finishing this keyboard that I would have one last go. This time I
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abandoned the idea of putting heatshrink under the metal sleeve which screws on
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to the connector itself. This made it too bulky and impossible to fix when
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shorts developed after screwing the thing together. Instead I wrapped the
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assembly with electrical tape, then tested for shorts once it was screwed
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together. I had to repeat this several times, undoing the tape, fixing shorts
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and re-assembling before I got it all to work. Then I put the heatshrink on over
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the outside of the metal sleeve to strengthen everything up. This time it was
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third time lucky and the cable works! Again, I designed it to be just the right
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length to loop around the Apple Magic Trackpad that I place between the halves
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of my keyboard. I had intended it to be oriented so that the loop went over the
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top edge of the Trackpad, <em>but</em> the section of the case next to the controllers is
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just a bit too bulky to allow the jack to be fully inserted when it is in that
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orientation. I’ll have to live with it being oriented around the bottom edge
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instead. It isn’t a practical problem, but it looks a little odd. Anyway, I
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don’t really care — I’m just jubilant that I finally got that cable assembled!</p>
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<p>I’m so happy with my new keyboard. It might seem ridiculous to go to such
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lengths to have coloured lights on my keyboard, but every time I go to my desk
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to work, the pretty lights cheer me up no end. I haven’t played with that aspect
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of my layout yet, but they could also have a functional role: you can change the
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colour of the lights when particular layers are activated, or when caps lock
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is engaged, or you can change the colour of particular keys to highlight groups
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of keys on layers. I’m happy with it just being pretty though, and the keyboard
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is as delightful to type on as my other Cornes, and has a more solid, robust feel.</p>
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<section class="footnotes" role="doc-endnotes">
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<hr>
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<ol>
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<li id="fn:1" role="doc-endnote">
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<p>As the first one I built donated its parts, the second will be the one I take to work once I am back in the office full time. <a href="#fnref:1" class="footnote-backref" role="doc-backlink">↩︎</a></p>
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</li>
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</ol>
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</section>
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