Assembly: plates, switches, and keycaps

No iron in this chapter. Today the two soldered boards from Chapter 10 become a keyboard-shaped object: plates, switches, screws, feet, keycaps. It is the most satisfying afternoon of the build, and it starts with a step that is not assembly at all.

Before anything else: test the electronics now

Here is the ping-pong this book warned you about, stated as plainly as possible. Stop. Go to Chapter 12. Do its flashing section now, for both halves. Then do its tweezer test. Then come back here to this paragraph.

The reasoning: flashing the firmware needs nothing but the bare boards and a USB cable, and once a board is flashed you can test every one of the 58 key positions by touching metal tweezers across the two contacts inside each hotswap socket. Each touch closes the circuit exactly as a switch would, and a letter appears in any text editor. Five minutes with tweezers proves every diode, every socket joint, every trace, and the controller, before the case is screwed shut around them. Skip this and discover a dead column after assembly, and your reward is unscrewing everything you are about to lovingly screw together. Builders who have done both orders do not debate this one.

If the tweezer test found dead spots, detour through Chapter 13 and fix them now, while every joint is still exposed. Rejoin here with two fully passing boards.

You are done when both halves are flashed and every one of the 58 positions produced a character under the tweezers.

Lab part 1: OLED covers and standoffs (10 minutes)

Most kits include a small acrylic or FR4 cover that floats above each OLED on short standoffs, protecting the glass from your thumbs. A standoff is a small metal tube threaded at both ends: a screw enters each end, and the tube holds two layers apart at a fixed height.

  1. If your acrylic parts wear a brown or blue protective film, peel it now. The film is easy to mistake for a scratched, cloudy finish; underneath is clear acrylic.
  2. Screw the OLED standoffs to the main PCB at the holes flanking the screen, then the cover onto the standoffs. Fingertip tight only.
  3. Exact stack order and standoff lengths vary by kit; when in doubt, the kit's guide photos settle it.

You are done when each screen sits under a firm cover that does not touch the glass.

Lab part 2: the top plate and the first four switches (20 minutes)

The top plate is the rigid layer with switch-shaped cutouts. Each switch clips into the plate, and its two metal pins continue down into the hotswap socket on the PCB below. Plate and PCB have to come together as a sandwich, and switches are what hold the sandwich together, so the order is: rest the plate loosely over the front of the PCB, then install switches through both layers at once.

Start with only the four corner switches of one half. They act as alignment pins for everything else, and doing four slowly teaches your hands the feel before you do fifty-four more.

  1. Look at the bottom of a switch: two metal pins plus plastic posts. The pins must be dead straight. A bent pin looks folded flat against the switch base, or kinked like a knee, instead of standing perpendicular. Straighten any bent pin with tweezers or small pliers before it goes anywhere near the board; it bends back once or twice without breaking.
  2. Hold the plate over the PCB at one corner position. Orient the switch the way Chapter 3 showed (pins toward the socket contacts; it only reaches the socket one way around).
  3. Support the socket from behind with a fingertip on the back of the PCB, directly under the switch position. All the insertion force should land on your finger, not on the socket's two solder joints.
  4. Press the switch straight down through the plate cutout until the plate clips click and you feel the pins slide home into the socket. It is a firm, positive push, not a violent one.
  5. Inspect: switch body flush against the plate, and on the back of the PCB, no pin visibly crumpled beside the socket instead of inside it.
  6. Repeat for the other three corners, then check the whole plate sits parallel to the PCB, an even gap all around.

You are done when four corner switches are seated flush, the plate is held square, and (since you flashed first) all four produce their letter when pressed with the board plugged in.

Lab part 3: populate the rest (30 to 45 minutes per half)

Now the remaining switches, same technique, one at a time: check the pins, support the socket from behind, press straight down, feel the click. Do not rush the pin check; a bent pin folds silently under the switch, the key feels perfectly normal and clicky, and it types nothing. Finding that after keycaps are on is an avoidable sadness.

The efficient rhythm, since your boards are flashed: keep the half plugged in with a keyboard tester open (Chapter 12 names a couple of free web testers, or any text editor works) and tap each switch right after seating it. Each tap paints a key on the screen. Insert, tap, confirm, next. By the time the last switch clicks in, the entire half is verified.

When a switch will not click in: the clinic

  • It stops a few millimetres proud of the plate and pushing harder feels wrong. Trust that feeling and pull the switch back out (straight up, wiggling gently). Nine times out of ten a pin has folded under. Straighten it, try again.
  • The switch seats but the key is dead. Pull it and look: a bent pin, or a pin that missed the socket opening and slid beside the plastic body. Straighten, re-aim, support the socket, press again. If the pin is straight and it is still dead, check the back: the insertion force may have pushed the socket off its pads, which means one reflow with the iron (Chapter 8) and a reminder about supporting from behind.
  • No switch in one area goes in nicely. The plate is misaligned by half a cutout. Back out the nearby switches, re-square the plate against the corner switches, try again.

You are done when all 58 switches sit flush with the plate and all 58 type their character.

Lab part 4: bottom plate, screws, and feet (15 minutes)

  1. Screw the M2 standoffs to the main PCB at the case holes (your kit's guide shows which holes and which length standoff; count them out first).
  2. Lay the bottom plate on and drive the M2 screws into the standoffs. Snug, then stop. The plates are FR4 or acrylic; FR4 strips its screw holes when muscled, and acrylic simply cracks, instantly and audibly. Tighten each screw until it seats, plus the smallest fraction more, and work in a criss-cross pattern so the plate pulls down evenly.
  3. Stick the rubber bumpons (adhesive feet) onto the bottom plate: one near each corner of each half at minimum. They stop the halves skating around the desk and give the screws clearance so they do not scratch it.

You are done when both halves are closed, nothing rattles when shaken gently, and each half sits flat without rocking.

Lab part 5: keycaps (15 pleasant minutes)

Keycap sizing is measured in units: 1u is one standard key width. The Lily58 is friendly here: on most sets, every position takes a 1u cap except the innermost thumb key on each half, which takes a 1.5u. Check your kit and keycap set, but if you sort your caps into "two 1.5u" and "everything else", you are nearly done thinking.

Two 1u caps are special: the ones with a small ridge or dimple on top, the homing bumps. On a normal keyboard they live on F and J, where your index fingers rest. Same idea here: they go on the home-row index positions, one per half, F on the left and J on the right in a QWERTY layout, so your hands can find home without looking. Which physical key that is depends on the keymap you flashed; with the default QWERTY layout it is the second column from the inside, home row, on each half.

Press each cap straight down onto its switch stem until it seats. No twisting: the cross-shaped stem is plastic and twisting rounds it out. If a cap goes on crooked, pull it straight off and reseat it.

You are done when every switch wears a cap, the two 1.5u caps are on the thumbs, and your index fingers find the bumps without looking.

Lab part 6: cables, and the one rule you never break

Two cables remain. The TRRS cable links the halves, carrying power and the signals that let one controller report the other's keys. The USB cable goes from one half to the computer.

Don't be confused. A TRRS cable and a TRS cable look identical from arm's length, and both plug into the Lily58's jacks without complaint. Count the black insulating rings on the metal plug: TRRS (tip, ring, ring, sleeve) has three rings dividing it into four contacts; TRS has two rings and only three contacts. The Lily58 uses all four, so a TRS cable, the kind on ordinary headphone and aux leads, leaves one signal disconnected and gives you a half-working keyboard with baffling symptoms. Use the cable from the kit, or buy one explicitly sold as TRRS (a 4-pole 3.5 mm audio cable is the same thing). By default in the Lily58 firmware, the left half is the master: plug USB into the left, and the right talks to it over TRRS. (Whether both halves need flashing, and how to make the right half the USB side instead, is Chapter 12's business.)

Now the sacred rule, and it deserves its explanation:

Never plug in or unplug the TRRS cable while USB is connected. Unplug USB first, every time.

The reason is mechanical. A TRRS plug is a metal cylinder divided into four contact bands, and as you slide it in or out, each band drags across every contact inside the jack on its way to its own. For a moment, the power band touches the ground contact, the data band touches the power contact, and so on: brief short circuits, made with live current if USB is powering the board. Most of the time nothing happens. Sometimes the controller or a component dies on the spot, and it is a completely unnecessary way to lose a board you just built. Cold cables only: connect TRRS, then USB; disconnect USB, then TRRS.

First power-up

Position the halves shoulder-width, connect the TRRS cable, take one breath, and plug the USB cable into the left half.

If you did the pre-assembly flash and test, you already know it works, and that robs nothing from this moment. The OLEDs light. You open an editor, put your fingers on the bumps, and type your name on a keyboard that did not exist last week, on solder joints your own hands made. Every builder does some version of typing "hello" and grinning at it. Take the photo; you earned it.

Type a slow sentence touching every key you can think of. If a straggler key plays dead now after passing the tweezer test, it is almost certainly a bent switch pin (the clinic above), not your soldering.

Takeaways

  • Flash and tweezer-test before assembly; Chapter 12 first, then this chapter. The ping-pong is deliberate and it saves disassembly.
  • Switches: check the pins, support the socket from behind, press straight down, and test each key as you go. Corners first to square the plate.
  • M2 screws snug, never cranked; acrylic cracks and FR4 strips.
  • Caps are all 1u except the two 1.5u thumbs; homing bumps go under your index fingers on the home row.
  • TRRS is only ever plugged or unplugged with USB out. No exceptions.
  • Left half takes the USB cable by default.

👉 The hardware is complete: a real, solid, clicking object. What makes it a keyboard, and makes it yours (layers, keymaps, the OLED display), is the firmware. On to Chapter 12, which you have already visited once and now get to finish.