LuxLibre

FlashKa Keychain v0.6 — Build guide from zero

This guide takes you from “I have never ordered a circuit board” to a working flashlight and slide remote in your hand. You do not need to know electronics or programming. You need patience, a soldering iron and a computer with the Chrome or Edge browser. Read the whole guide once before you order anything.

Status: designed, not yet built. Nobody has assembled a FlashKa yet. Everything in this guide is checked by software only (chapter 13, section 13.7), so you may be the first to build one. Where a step or a behaviour is untested, the guide says so. Please tell the project what you find (section 16).

FlashKa v0.6, seen from the USB-C side

Render, not a photo: FlashKa has not been built yet. Every picture of the light in this guide is a computer render made from the design files. The finished light seen from the USB-C side (the buttons are on the face underneath): 94.4 × 20 × 16 mm, black anodised aluminium, a white LED and a small green laser in the head, USB-C charging, and Bluetooth for the phone app and for presenting.

0. What you are building

FlashKa is a keychain flashlight with a green laser pointer. Version 0.6 adds a second job: it turns slides. In presenter mode the light is a Bluetooth keyboard, and the laser stays the pointer.

   
Size 94.4 × 20 × 16 mm, about 50 g with cells
Buttons three stainless-steel buttons on the bottom face: › next, ● main, ‹ previous
Ring two RGB LEDs shine through a ring around the main button and show what the light is doing
Main light Luminus SST-20 LED, 3 mA (moonlight) to 2.2 A (turbo, short bursts)
Laser green 520 nm module, Class 2 (≤ 1 mW), with a hardware safety switch
Presenter mode the light is a Bluetooth keyboard: › next slide, ‹ previous slide, ● black screen; the laser is the pointer
Battery two LP601646 lithium-polymer cells in parallel, about 800 mAh
Charging USB-C, about 300 mA, status shown on the ring
Brain ESP32-C3 module with Bluetooth Low Energy
Phone and computer app a web page: no app store, works in Chrome or Edge (Android, Windows, Mac, Linux)
Firmware updates from a web page over the same USB-C cable: no programmer needed

How it is made:

Hold the light with the bottom face up and the head pointing away from you (at the screen, when you present). The row of buttons then reads, from the head to the tail: › next · ● main · ‹ previous. Next is towards the screen. Previous is towards you. The seams, rivets and stencils on the body are styling. The marks that matter are SAFE and ARM at the slide switch, LASER near the head, the chevrons at the buttons and the laser warning label.

The bottom face

Render. The bottom face with its three buttons, head (LED and laser) at the upper right. From the head to the tail: › next, ● main inside its light ring (shown cyan), ‹ previous, and the cream plug that closes the radio window in the floor. The chevron beside › points towards the head, the one beside ‹ towards the tail.

If you know the v0.5 guide: chapter 13, section 13.1 lists what changed and why.

1. Before you spend money

Cost. The workbook FlashKa_Parts_List_v0.6.xlsx lists every part and every fee. The short version (delivery to Lithuania, EU, 21 % VAT; prices of unchanged parts read on 2026-10-14, new lines on 2026-10-18):

  one light two lights five lights
Everything, including shipping, VAT and set-up fees 620.21 USD (554.35 EUR) 775.28 USD (692.95 EUR) 1,194.99 USD (1,068.10 EUR)
Per light 620.21 USD 387.64 USD (346.48 EUR) 239.00 USD (213.62 EUR)
Tools you may not have yet (one-time) about 135 USD    

Version 0.5 cost about 530 USD for one light. v0.6 costs about 90 USD more:

One light is expensive because the fixed costs (assembly set-up, stencils, three parcels from JLC, several marketplace parcels) are paid once, whatever the quantity. JLCPCB makes at least 5 boards and assembles at least 2. Building with friends brings the price down a lot.

Many prices are estimates. The shops show their price only after you upload the files, and some pages could not be read. The stainless caps (about 28 USD for the caps of one light with a spare of each), the laser marking, the bare boards, the aluminium parts and the marketplace parts are estimates. The workbook marks them (blue on amber). Replace them with the real quotes before you pay.

Time and the order of the orders. Building takes one or two evenings (the glue needs time to harden); the waiting takes longer. Order in this sequence (the workbook’s sheet Ordering checklist has the same steps):

  1. Day 1: order the bought parts (section 6) and the circuit boards (section 3), about 2 weeks. Also try the two cap files in the JLCCNC instant quote (section 4, step 2); it costs nothing.
  2. When the cells, the LED board and the laser have arrived (2–5 weeks from AliExpress): measure them (section 8). They must match the specification, because the body is made for them.
  3. Then order the body and caps (section 4; 10–12 days) and the print kit (section 5; a week).

At every checkout choose shipping with taxes and duties paid (DDP / “tax included”). The cost figures above assume it.

Skills. Soldering wires to pads (practise on scrap first), using a small screwdriver, cutting two tiny pieces of rubber with a sharp knife, gluing with a very small amount of epoxy, and following instructions exactly. Nothing else.

Safety — read this. The project’s safety notes are in SAFETY.md at the root of the LuxLibre repository. The design rules named in this guide (for example LAS-1) are in docs/design-rules.md at the same root.

2. The files

Everything you upload is ready in the folder order_files/ of the package, one subfolder per shop. The paths below start in that folder.

Shop File What it is
JLCPCB 1_JLCPCB/FlashKa_main_gerbers.zip the circuit board drawings (Gerber files)
JLCPCB 1_JLCPCB/BOM_JLCPCB.csv list of the parts to mount (34 lines, 68 parts per board)
JLCPCB 1_JLCPCB/CPL_JLCPCB.csv where each part goes and how it is turned
JLCCNC 2_JLCCNC/FlashKa_tray.step + FlashKa_tray.pdf aluminium tray: 3D model + drawing (2 sheets)
JLCCNC 2_JLCCNC/FlashKa_lid.step + FlashKa_lid.pdf aluminium lid: 3D model + drawing
JLCCNC 2_JLCCNC/FlashKa_cap_main.step + .pdf stainless main cap (the ● button): 3D model + drawing
JLCCNC 2_JLCCNC/FlashKa_cap_slide.step + .pdf stainless slide cap (the › and ‹ buttons): 3D model + drawing
JLCCNC 2_JLCCNC/FlashKa_marking_lid_class2.dxf laser marking of the lid: warning label, stencils, rivets
JLCCNC 2_JLCCNC/FlashKa_marking_bottom.dxf laser marking of the bottom face: chevrons, rivets
JLCCNC 2_JLCCNC/FlashKa_marking_minus_y.dxf laser marking of the USB-C side
JLCCNC 2_JLCCNC/FlashKa_marking_plus_y.dxf laser marking of the laser side: SAFE and ARM
nobody 2_JLCCNC/FlashKa_marking_lid_class3R.dxf a Class 3R label; do not use (see section 4)
JLC3DP 3_JLC3DP/FlashKa_print_kit.stl the seven resin parts on thin rods, as one part
JLC3DP 3_JLC3DP/FlashKa_laser_sleeve.stl only if your laser module is 4.5 mm instead of 6 mm

Files you keep:

File What it is
app/flashka-flasher.html the firmware installer (open it in Chrome or Edge)
app/flashka-app.html the phone and computer app (open it in Chrome or Edge)
FlashKa_Parts_List_v0.6.xlsx every part, price, link and fee

(The same files, with all the source data behind them, are also in production/ and cad/. Each folder in order_files/ has a short README.txt.)

3. Order 1 — circuit boards with parts mounted (JLCPCB)

  1. Make an account at jlcpcb.com and log in.
  2. Click Order now (or “Instant quote”) and Add gerber file. Choose order_files/1_JLCPCB/FlashKa_main_gerbers.zip. Wait until the picture of the board appears (24.0 × 16.5 mm should be detected automatically).

  3. Set these options (leave everything not listed at its default):

    Option Choose
    Base material FR-4
    Layers 4
    PCB qty 5 (the minimum)
    PCB thickness 0.8 mm
    PCB color green (cheapest; others are fine)
    Surface finish ENIG (flat gold pads, needed for the Bluetooth module)
    Outer / inner copper 1 oz / 0.5 oz
    Via covering Tented
    Min via hole size/diameter the value JLCPCB detects (0.2 mm hole, 0.45 mm via: no surcharge)
    Remove order number No (the default). JLCPCB prints a small number on a free spot of the board; it stays inside the closed body

  4. Scroll down and switch PCB Assembly on:

    Option Choose
    PCBA type Standard (parts on both sides need Standard)
    Assembly side Both sides (the three switches and the two ring LEDs are on the bottom side)
    PCBA qty 2 (the minimum), or as many lights as you build if more
    Tooling holes Added by JLCPCB
    Confirm parts placement Yes (an engineer checks the orientation of every part; recommended)
  5. Click Next, then upload BOM = order_files/1_JLCPCB/BOM_JLCPCB.csv and CPL = order_files/1_JLCPCB/CPL_JLCPCB.csv. Click Process BOM & CPL.

  6. The parts list appears: 34 lines. Every line should show a matched part with stock.

    Two lines need a closer look, because the shop pages for them could not be read when the workbook was made:

    • C115357: the three push switches SW1–SW3 (Alps SKRKAEE020). There is no simple substitute. Ask in the project before you pick another switch, because the footprint must match.
    • C25104: the two 330 Ω resistors. Any 330 Ω, 1 %, 0402 resistor can replace it.

    If another part is out of stock, the workbook (sheet Main PCB BOM) names an alternative. For example, the Bluetooth module C2838502 (ESP32-C3-MINI-1-N4) can be replaced by C41349510 (ESP32-C3-MINI-1-H4X), a drop-in alternative. Five small parts had low or zero retail stock at LCSC on 2026-10-14 (C15850, C15195, C1525, C11702, C485117). JLCPCB has its own warehouse, and the upload page shows its real stock.

  7. Check the placement preview. JLCPCB draws every part on the board. For each chip, the small dot or line that marks pin 1 must sit on the pin-1 mark of the board. The pads of every part must fall on the pads of the board. If a part is turned, select it and use Rotate.

    Look closest at the parts whose drawing in JLCPCB’s library is often turned against KiCad’s (DFM-7): the Bluetooth module U4, the small chips U1, U2, U3, U5, the transistors Q1, Q2, Q4, Q5, the USB-C socket J1, the three switches SW1, SW2, SW3 and the two ring LEDs LED3, LED4.

    If you are unsure, do not worry. With “Confirm parts placement” an engineer checks it and sends you a picture before production.

  8. Save to cart, pay. The board order (5 boards, 2 of them assembled, all parts included) costs about 174 USD before shipping and VAT (the workbook, sheet JLCPCB order, shows every line; the bare-board price is an estimate). Choose a shipping method with taxes paid (DDP).

Why the gold surface (ENIG)? The Bluetooth module sits on a big flat ground pad under its belly. Tin (HASL) surfaces are bumpy and the module can end up crooked. ENIG costs a few dollars more and avoids that.

4. Order 2 — the aluminium body and the stainless caps (JLCCNC)

The tray and the lid are aluminium parts. The three caps are tiny stainless-steel parts that you press with your thumb. All of them come from order_files/2_JLCCNC/.

  1. Go to jlccnc.com, log in with the same account, Instant quote → CNC machining.

  2. Try the caps first. They are very small: 7.0 mm long, with a head 5.8 mm (main cap) or 3.4 mm (slide cap) across. JLCCNC’s own pages disagree on whether it turns parts that small. One page gives a minimum part size of 5 × 5 × 1 mm. Another says turned metal parts must be longer than 20 mm. Upload FlashKa_cap_main.step and FlashKa_cap_main.pdf, then FlashKa_cap_slide.step and FlashKa_cap_slide.pdf, and read the answer. JLCCNC matches a drawing to a 3D file by its name, which is why both are called the same.

    Option Choose
    Process CNC turning
    Material stainless steel SUS304
    Surface finish bead blasting; no coating (JLCCNC offers no polishing or passivation for stainless)
    Quantity main cap: 1 per light + 1 spare; slide cap: 2 per light + 1 spare

    If the quote refuses the caps by size, you have two ways out. Send the same STEP files and PDF drawings to another CNC shop (PCBWay, Xometry or a local workshop can make them), or use the resin caps from the print kit (section 5). The resin caps have the same shape. They are not stainless and not tested.

  3. Upload the tray and the lid the same way: FlashKa_tray.step + FlashKa_tray.pdf and FlashKa_lid.step + FlashKa_lid.pdf. The drawings carry the threads and the tolerances that JLCCNC needs.

  4. For both parts choose:

    Option Choose
    Process CNC milling
    Material Aluminum 6061-T6
    Surface finish Bead blasting + anodizing, black (the drawings ask for type II, 8–12 µm)
    Tolerance ISO 2768-m (standard)
    Threads yes. Write in the remark: “4 × M1.6×0.35 in the tray, 1 × M2×0.4, see drawing; tapped before anodising, screws must fit after finishing (drawing note 3)”
    Quantity one of each per light. Order one set first, test-fit it with your real parts, then order the rest

    Bead blasting shoots tiny glass beads at the part for a matt surface. Anodising grows a hard, black oxide layer on the aluminium.

  5. Laser marking after anodising, from the four DXF files (a DXF file is a 2D drawing):

    Face File
    lid FlashKa_marking_lid_class2.dxf
    bottom face of the tray FlashKa_marking_bottom.dxf
    USB-C side (−Y) FlashKa_marking_minus_y.dxf
    laser side (+Y) FlashKa_marking_plus_y.dxf

    The marking removes the black layer, so bare aluminium shows. It carries the laser warning label, the rivet dots and stencils, and the marks that matter: SAFE and ARM at the slide switch, LASER near the head and the chevrons at the two small buttons.

    If JLCCNC does not offer laser marking for your order, print an adhesive label with the label text (LASER RADIATION, DO NOT STARE INTO BEAM, CLASS 2 LASER PRODUCT, 520 nm P < 1 mW EN 60825-1:2014) and mark SAFE, ARM and the chevrons by hand.

  6. JLCCNC answers with a price within a day. Two things can come up:

    • If they warn that a wall is thin: the thinnest metal wall in the design is 0.8 mm and is intended. Confirm it in the quote chat.
    • If they say M1.6 threads are not possible, accept plain holes. The drawing gives the tap-drill size, and you cut the thread yourself with an M1.6 hand tap (about 10 USD for a tap set).

Laser class. LuxLibre rule LAS-1 allows Class 1 or Class 2 lasers only (visible, at most 1 mW). The label on the lid says Class 2, and it is only true if your module really emits at most 1 mW (rule LAS-3: measure it). The folder also holds a Class 3R label file. It exists only so that a builder who measures more than 1 mW has a correct label. A module that strong should not be used: send it back and buy another one. Do not order the Class 3R file.

5. Order 3 — the plastic parts (JLC3DP)

  1. jlc3dp.com → Instant quote, upload order_files/3_JLC3DP/FlashKa_print_kit.stl. It is one file and one part: seven resin parts joined by thin rods (sprues). (Only if your laser module is 4.5 mm instead of 6 mm thick, also upload FlashKa_laser_sleeve.stl.)
  2. Material: SLA resin, 8001 (translucent), as printed. Do not choose the “transparent” 8001: it is sanded and oil-sprayed, and costs more. The quote may warn about thin flanges (the resin caps have 0.6 mm flanges). Accept it, or ask the shop.
  3. Quantity: one kit per light, plus one spare kit (they are cheap). You cut the parts apart at home with side cutters.

What is in one kit:

Part What it does
Light tube (ring) carries the light of the two ring LEDs down to the bottom face, where it shows as a ring around the main button
Radio window insert closes the window in the lid; lets the Bluetooth signal out
LED spacer ring sits between the LED board and the glass window
Antenna spacer, with a plug keeps the cells away from the antenna; its plug closes the radio window in the floor
Main cap, resin same shape as the stainless main cap: a back-up, and a fit check
Slide caps, resin (2) same shape as the stainless slide caps

6. Order 4 — parts you buy ready-made

Search these on AliExpress (or any electronics shop). The workbook (sheet Bought parts) has a search term, a link example and the typical price for each. Order them first (section 1) and measure what you receive before you order the aluminium body.

Part Exact specification Quantity per light
LiPo cells LP601646 (6.0 × 16 × 46 mm), 3.7 V, about 400 mAh, with protection board and wire leads, rated for at least 2 C continuous (0.8 A per cell; 3 C if you want the Extreme profile); the whole cell including its protection board must fit 6.0 × 16 × 47 mm 2 (+1 spare)
LED board Luminus SST-20 (white, 5000–6500 K) on a 10 mm round copper DTP board (direct thermal path), 1.6 mm thick 1 (+1 spare)
Laser module 520 nm green, 6 × 12 mm body, with a built-in constant-power (APC) driver for a 3.0–4.2 V supply, Class 2 (≤ 1 mW), with wires. Ask the seller for a measured output power 1
Window flat glass disc 10.0 mm × 1.0 mm (AR-coated “flashlight lens” is best); no curved lens 1
Lid screws M1.6 × 4 mm countersunk, stainless (A2) 4 (+4 spare)
Laser set screw M2 × 2 mm set screw, cup point, hex socket (M2 × 2.5 also fits; longer ones stick out of the bottom) 1
Wire 28 AWG PTFE, red and black (usually sold as 5 m rolls; one light needs about 0.3 m) –
Thermal tape 0.15 mm, double-sided, thermally conductive, at least 10 mm wide (or a little thermal paste), for the LED board a little
Kapton tape, thin double-sided foam tape insulation; holds the cells (foam: 1 mm × 10 mm) a little
Clear epoxy two-part, 5 minute, small syringe (or a clear UV-curing adhesive): glues the tube, the radio window insert and the glass window. Not cyanoacrylate (white bloom) a little
Silicone gap pad 1.0 mm thick, Shore 00 70–80 (soft; the thermal rating does not matter), a sheet of at least 20 × 20 mm. You cut 8.8 × 12.4 mm from it for the module-can boss 1 piece
Silicone rubber sheet 1.0 mm thick, Shore A 70 (firmer), at least 20 × 20 mm. You cut 3.7 × 3.2 mm from it for the front boss 1 piece
Silicone adhesive small tube, neutral cure (no vinegar smell: the acid kind can attack the copper of the board). Sticks the two pads a drop per pad
Split ring or lanyard stainless split ring, 20–25 mm, wire at most 3 mm thick, through the tail slot 1

The two pads hold the circuit board down against the lid (section 12.8). The firmer pad goes on the small boss, the softer one on the big boss.

7. Tools

Tool Why About (USD)
Soldering iron with a fine tip (temperature-controlled, e.g. Pinecil or TS101) the wires 35
Solder 0.5 mm with flux core clean joints on small pads 8
Flux (gel syringe or pen) makes the solder flow on small pads 6
Desoldering braid (wick) to remove solder if a joint goes wrong, and the temporary wires of the bench test 3
Fine tweezers hold small parts and wires 5
Flush side cutters wires, and the print kit 5
Wire stripper (fine), for 28 AWG strip the wires without cutting the strands 7
Hobby knife or scalpel and a small cutting mat cut the two silicone pads to size 7
Precision screwdriver and hex key set M1.6 countersunk lid screws (check the head type you bought); 0.9 mm hex key for the M2 set screw 8
Digital caliper measure the cells, the LED board, the laser and the pads 12
Multimeter check cell voltage, polarity and shorts 15
Laser safety glasses for 520 nm (OD 4 or better, CE / EN 207 marked) laser tests 14
Isopropyl alcohol 99 %, cotton swabs cleaning flux and wiping off glue 6
USB-C cable that carries data firmware; many cheap cables only charge 4
Computer with Chrome or Edge (Windows, macOS, Linux or ChromeOS) firmware installer –

These tools add up to about 135 USD. Optional and not counted: a magnifier or USB microscope (about 15 USD; good for checking the small parts), a bench power supply with a current limit (about 30 USD, for a careful first power-up), a laser power meter for 520 nm (about 45 USD, to check that the module is really Class 2), and M1.6 and M2 hand taps (about 10 USD, only if JLCCNC cannot cut the threads).

8. When the parcels arrive — check

9. Step 1 — Prepare the cells

The flashlight takes its power from the cells, also while you install the firmware. So the cells come first.

The pads you will solder. The front end of the board is the end with the LED pad J3 (the head of the light). The rear end is the end with the cell pads J2. Keep this picture next to you. Sections 11 and 12 use it again.

Wiring pads

A drawing of the two sides of the board, not a photo. Red pads are +, dark blue pads are −. J2: cells, J3: the LED (one pad on each side, at the same spot), J5: the laser. The small “+” and “−” printed on the board are tiny and partly covered by solder mask: trust the picture.

  1. Check polarity. Red = +, black = −. Confirm with the multimeter (red probe on the red wire: the reading must be positive).
  2. Match the voltages. Both cells within 0.1 V. If they differ more: solder only the fuller cell (steps 3–6), install the firmware (section 10) and charge it until the ring is steady green; unsolder it, do the same with the other cell; then both are full and equal.
  3. Check the board for a short. Set the multimeter to the beep (continuity) setting and touch the two J2 pads (see the picture above). It must not give a steady beep. (On the resistance setting, a reading near 0 Ω is a short. A reading that climbs slowly is normal: the capacitors on the board are charging from the meter.) If it beeps, stop and look at the board under a magnifier. Do not connect the cells.
  4. Shorten the wires to about 40 mm (cut one wire at a time: cutting both at once with the same cutter short-circuits the cell!). Strip 2 mm, twist, tin with solder.
  5. Twist the two red wires together and the two black wires together (still one at a time).
  6. Solder to the board. The cell pads J2 are the two big pads at the rear end, in the corner on the bottom side (the side with the USB-C socket and the switches). J2 + (red wires) is the pad nearer the long edge with the USB-C socket; J2 − (black wires) is the pad nearer the middle of the board (see the picture). Put a little flux on the pad, hold the tinned wire on it, touch with the iron for 2–3 seconds. Red first, then black.
  7. The board is now powered. Nothing lights up yet, because the firmware is not installed. Lay the board and cells on a non-metal surface.

If anything gets hot, smells or smokes: pull the cells away with pliers by the wire, put them in the metal box. A reversed cell destroys the board. That is why step 1 matters.

Optional, for the first power-up. Nobody has powered a FlashKa yet. If you own a bench power supply with a current limit, you can follow the bring-up of the LuxLibre testing guide (bring-up of a new board) before you solder the cells: set about 3.7 V and a current limit of 100 mA on the J2 pads. This guide goes on directly with the cells.

10. Step 2 — Install the firmware (no experience needed)

The firmware is the program that runs in the flashlight. You install it from a web page, through the flashlight’s own USB-C socket. Nothing to download, nothing to install on your computer.

You need: the board with the cells soldered on (step 1), a USB-C cable that carries data, and a computer with Google Chrome or Microsoft Edge. (Firefox and Safari cannot do this, and phones cannot flash.)

1. Open the installer. Open app/flashka-flasher.html from the package in Chrome or Edge (double-click the file; if it opens in another browser, right-click → Open with → Chrome). The project also publishes the same page at https://dompka.github.io/LuxLibre/flashka/flashka-flasher.html, and you can put the app folder on any website with https (see docs/web_apps.md).

2. Plug in. Connect the flashlight’s USB-C socket to the computer. The ring starts breathing red slowly (charging). If the firmware was not installed yet, it may stay dark; that is normal.

3. Connect. Click Connect. A small browser window lists the serial ports. Choose:

and click Connect in that window. The page says “Flashlight found (ESP32-C3, 4MB memory)”.

Installer, step 3

The installer after Connect (a screenshot of the page): it names the firmware inside the page (FlashKa firmware v0.6.0, 534,736 bytes) and shows two green checks.

4. Install. Leave the box “Factory reset” unticked (every installation already puts the settings back to the factory defaults). Click Install firmware. A progress bar runs for about one minute. Do not unplug while it runs.

5. Done. The page says “Installed and checked”. Unplug the cable and plug it in again. The ring breathes red (charging) or shows steady green (full).

That’s it. To update the firmware later, do exactly the same with a newer installer page.

Every installation resets the saved settings (your custom profile) to the factory defaults and makes the light forget the paired computers. After an installation, remove “FlashKa” from the Bluetooth list of each computer and pair it again (section 13).

If “Connect” shows no port

If the port appears but connecting or installing fails

Force the chip into its built-in installation mode (it cannot be broken this way):

  1. Unplug the USB cable.
  2. Press and hold one of the three push switches on the bottom side of the board. Any of the three works; the middle one is the main button ● (the picture in section 9 shows the row). On the bare board press the switch with a plastic toothpick. In a closed light, hold the round metal button ●.
  3. While holding it, plug the USB cable in. Keep holding for about a second, then release.
  4. Click Connect again and choose the port. Then Install firmware.
  5. When it is done, unplug and replug the cable.

Why this works: plugging in USB restarts the chip (a small circuit on the board does that), and a chip that starts with a button pressed waits for new firmware instead of running the old one. Every press of any of the three buttons pulls the same pin low.

What happens inside (for the curious)

The ESP32-C3 has a USB port built in. The installer page uses your browser’s Web Serial feature and the open-source esptool-js to write one file (flashka-fw-v0.6.0-merged.bin, 534,736 bytes: bootloader, partition table and program) to address 0 of the module’s 4 MB flash memory. The file sits inside the page. The page checks its fingerprint (SHA-256, e21058791bab990439835fbd977eecfed385af5837405e36ae923cb6083a8fdd) before writing.

11. Step 3 — Test on the bench (lid open, nothing in the body yet)

Find a fault now, while the board is still lying on the table. Work on a non-metal surface. Keep the USB cable unplugged unless a step says so.

How to click a bare switch. The three switches are on the bottom side of the board, in a row: › next, ● main (the middle one) and ‹ previous. Press a switch with the tip of a plastic toothpick. A click is a press shorter than 0.4 s; the pause between the clicks of one gesture is at most 0.4 s. A hold is longer. If a gesture does not work, you were too slow: click faster, like a double-click.

11.1 Charging and the ring

  1. Plug in the USB cable. You should see: the ring (the two small LEDs next to the main switch) breathes red slowly, about once in 3 seconds. That means charging. Steady green means the cells are full.
  2. Unplug the cable.

11.2 Ring colours and gestures (no wires needed)

With the light off, do each gesture and look at the ring:

You do You should see
● 4 clicks red × 3 (lockout on)
● 4 clicks again green × 3 (lockout off)
● 3 clicks blue × 2 (a Bluetooth window opens for 2 minutes), then a blue double blink every 3 s
› or ‹ click nothing: › and ‹ do nothing while the light is off

Red, green and blue must look like red, green and blue. If a colour is wrong (for example the lockout shows green first), the pad map of the ring LED differs from the plan. That is a known open point of the design (chapter 13, section 13.9, item 5). Do not assemble. Write down what you see and report it (section 16). The mixed colours (white, yellow) may look tinted: the colour balance is not tuned yet.

To check Bluetooth with the app (optional): open app/flashka-app.html in Chrome or Edge on a computer, click ● three times (ring blue × 2), click Connect in the app and choose FlashKa-XXXX. You should see: the battery percentage, the voltage and the temperature. (A phone needs the app from a web address: section 14.)

Do not click ● once for now. A single click switches the main LED on, and no LED is connected yet. Nobody has tried that on a real board, so leave it for the LED test below.

  1. Solder a red wire (60 mm) to the + pad and a black wire (60 mm) to the − pad of the LED board, on the LED side, with the wires pointing away from the board’s centre. You will use the same wires in the body later.
  2. Solder the black wire (LED −) to the bottom pad of J3 and the red wire (LED +) to the top pad of J3 (the same spot on both sides of the board, at the front end; see the picture in section 9).
  3. Click ● once. You should see: the LED lights at Low (30 mA), and the ring shows green for 2 seconds (battery above 50 %; yellow means 20–50 %, red below 20 %).
  4. Click › once: one step brighter (Medium, 200 mA). Click ‹ twice: Low, then Moon (3 mA, very dim). A third ‹ does nothing: the levels do not wrap.
  5. Click ● again: the LED goes off. Now click › and ‹: nothing happens (no light, no ring).

Do not run High or Turbo on the bench, and keep Medium to a few seconds. Without the aluminium body the LED board has nothing to shed heat into. Do not look into the LED from close range.

Warning — laser. Put on the 520 nm safety glasses first. Point the module at a matt dark card at the end of the table. Nothing shiny in the beam, nobody in line with it. Never look into the beam. The laser is on only while you hold the gesture.

  1. Solder the module’s wires to J5, the pair of narrow pads on the bottom side: red to the pad nearer the front end (+), black to the other one (−). Let the module lie on the table, pointing at the card.
  2. Push the knob of the slide switch S2 towards the rear (cell) end: ARM.
  3. With the light off and not locked: click ●, then press ● again and hold it. You should see: a green dot on the card and the ring steady red, for as long as you hold. Let go: both go off.
  4. Push S2 to the front end: SAFE. Repeat the gesture. You should see no green dot. (The ring may still turn red: the firmware cannot see S2.)
  5. If the dot comes on with S2 at the front end, your switch works the other way round: then the SAFE and ARM marks on the body would be wrong. Do not use that light as it is. Report it (section 16).

11.5 Presenter mode (pairing and keys)

Unplug the USB cable first: plugging in USB restarts the chip and ends presenter mode. The cells must be above 3.20 V (presenter mode is refused below that: one red blink).

  1. Press ‹ and › together for 2 seconds (two toothpicks, or two fingertips). You should see: the ring blinks magenta twice, then breathes cyan, slowly. The light waits for a computer.
  2. On the computer open the Bluetooth settings and pair FlashKa-XXXX (XXXX is the end of the light’s Bluetooth address). On Windows 10 or 11: Settings → Bluetooth & devices → Add device → Bluetooth. There is no PIN; the computer may ask you to confirm. The steps for other systems are in section 13.4. You should see: the ring blinks cyan twice and goes off.
  3. Open a text editor with a long text. Click › (quick press): the page moves down by one screen (Page Down). Click ‹: it moves up (Page Up). Click ●: a letter b is typed. Each key press makes a short white blip on the ring. Each click must give exactly one key.
  4. Hold › for about a second: one F5 is sent. Hold ‹ for about a second: one Esc.
  5. Press ‹ and › together for 2 seconds: the ring blinks magenta twice. The light is a flashlight again.

Nobody has tried the pairing with a real FlashKa yet; if it does not work, see section 15.

11.6 Clean up

Unsolder the LED wires from J3 and the laser wires from J5 with the desoldering braid: you need them with free ends in section 12. Check that nothing bridges the pads. Lock the light (section 12.0).

12. Step 4 — Assemble

Work on a clean towel. The order matters, because some joints cannot be reached later and the loose caps fall out if the tray is turned over. Four steps use glue (the tube, the glass window, the radio window insert, the two pads): give each the time on its pack to harden, and do the other work meanwhile. Close the lid last.

12.0 Make it safe first

The cells are connected, so the board is live. Push the knob of the slide switch S2 towards the front (LED) end: SAFE, and lock the light with 4 quick clicks on ● (red × 3). It stays locked until section 13.

Exploded view

Render, exploded view. The window, spacer ring, LED board and laser go into the head from the front. The light tube and the three stainless caps sit in the floor. The board drops into the tray. The antenna spacer, the two cells and the lid follow.

12.1 Cut the print kit

Cut the seven parts off their rods with side cutters, close to the part. Trim the stubs flat with a knife. The picture shows which part is which. On the light tube, the end face (the end without the rim) is the glowing ring. Leave no stub on it or on the rim.

The print kit

Render, the print kit as ordered. From the left: radio window insert, LED spacer ring, antenna spacer with its floor plug, light tube, resin main cap, two resin slide caps.

12.2 Glue the tube into the floor

The tube is the first new step. The caps and the board go on top of it, so it comes first.

  1. Try the tube in the large floor hole without glue. Put it in from the inside of the tray, with the end that has no rim going first. The rim ends up in a step (the counterbore) around the hole. The tube must go in by its own weight, with a little play. The ledge it rests on is only 0.2 mm wide. If it does not go in, do not press it. Take the tube of the spare kit. If that is tight too, rub the body of the tube (not the rim, not the end face) with fine sandpaper on a flat surface for a second and try again.
  2. Take the tube out. Put the tray open side up on a sheet of paper on a flat table, so that the bottom face lies flat.
  3. Mix a very small amount of clear epoxy. With a toothpick put a thin ring of it on the ledge around the hole (the rim of the tube will sit on it). Do not get any glue in the bore of the tube or on its end face.
  4. Put the tube in again in the same way and let it settle by its own weight. Do not press. The underside of its rim sits on the ledge, and its end face must be flush with the bottom face. Wipe any glue that shows with a cotton swab and isopropyl alcohol at once.
  5. Leave it to harden. Do not turn the tray over until the epoxy is hard (an hour or more, see the pack).

You should see: from below, a clean ring of translucent resin around a round hole, level with the floor. From above, the rim sits flat in its step.

12.3 LED board

If you did not do this in section 11.3: solder a red wire (60 mm) to the + pad and a black wire (60 mm) to the − pad of the LED board, on the LED side, with the wires pointing away from the board’s centre. Hold the board so that + is at 12 o’clock (top, lid side) and − at 6 o’clock.

12.4 Into the head

From the front of the body, push the red wire into the upper groove of the big bore and on through the upper hole into the inside of the body; the black wire through the lower groove and hole. Put a thin layer of thermal paste (or the thermal tape) on the back of the LED board and push the board to the bottom of the bore, wires pulled gently from inside.

12.5 Spacer ring and window

Insert the spacer ring (its notches go over the two solder joints), then the glass window. Fix the window with three tiny dots of clear epoxy or UV resin at its edge. Keep the glass clean.

12.6 Laser

Push the module into the small bore beside the LED bore, on the S2 side, from the front, wires first, until its front sits 0.2–0.3 mm behind the front face (no thermal paste needed: a Class 2 module makes almost no heat). Tighten the M2 × 2 set screw from the bottom face of the body, near the head, with the 0.9 mm hex key. Be gentle: the module body is soft brass. The epoxy of the tube must be hard before you turn the tray for this.

12.7 Caps

Now the stainless caps, from inside, with the tray open side up on the table.

  1. Main cap: drop it, head down and stem up, into the light tube. It falls until its flange rests on the step inside the tube.
  2. Slide caps: drop one into each of the two small floor holes in the same way, head down. The two are identical. The flange rests on the inner face of the floor.
  3. Check every cap. Tilt the tray gently: each cap must slide by itself, without catching. Seen from the side, each domed head should stand about 0.1 mm out of the floor, roughly the thickness of a sheet of paper. A cap has a free play of 0.30 mm by design: it moves that far before it reaches its switch.

The caps are loose parts. Only the flange holds a cap. Do not turn the tray over before the board is in, or the caps fall out. If one falls out, drop it in again.

12.8 Lid: radio window insert and pads

Radio window insert. Glue the radio window insert into the window of the lid, from the inside (epoxy on the flange, not on the top face). Let it harden.

The pads

Render, the open tray seen from the lid side, head on the left. The two hold-down pads are drawn on the board: the big grey one on the metal can of the Bluetooth module and the small salmon one next to the › switch. In the finished light they sit on the lid bosses and press the board down.

Pads. Under the lid there are two raised blocks, the bosses. A boss is a small block that presses on the board through its pad. The big one is 8.8 × 12.4 mm and goes over the metal can of the Bluetooth module; the small one is 3.7 × 3.2 mm and goes next to the › switch.

  1. Cut the pads on the cutting mat with the knife and a ruler, in one firm stroke per edge (do not saw). Measure with the caliper:
    • from the 1.0 mm silicone gap pad (soft): 8.8 × 12.4 mm, for the big boss;
    • from the 1.0 mm silicone rubber sheet (firmer): 3.7 × 3.2 mm, for the small boss.
  2. Put a small drop of neutral-cure silicone adhesive on each boss, spread it thin, and press the matching pad on. Keep the adhesive off the board and off the rim of the lid.
  3. Leave the lid face up until the adhesive has skinned over (see the pack; this is a good moment to do the other steps). The pads must stay on the lid when you open it later.

When the lid closes, each pad is compressed from 1.0 to 0.8 mm. The two pads then press on the board with about 34 N together (calculated). That keeps the board on its ledges when you press a button.

12.9 Wires to the board (bottom side first)

12.10 Board in

The slide switch S2 sticks out of the board edge on the laser side (the side opposite the USB-C socket).

  1. Tilt the board a little (about 5°) with the S2 side low, front end towards the head.
  2. Push the front edge under the head step and guide the S2 knob into its slot in the side wall first.
  3. Swing the USB-C side down. The USB-C socket goes into its opening in the wall, the three switches come to rest above the three caps, and the long edges lie on the ledges. Do not force it. If it does not go in, look for a wire in the way.
  4. The board must lie flat and must not rock. Without the lid it is not held down, so a press on a cap may only lift it. The real test of the buttons is in section 12.13.

12.11 Antenna spacer and cells

  1. Push the antenna spacer in behind the board. The module’s antenna (it sticks out of the board’s rear edge) sits in the U. The plug on the underside of the spacer goes into the window in the floor and must end level with the floor. The cell wires pass through the notch at the lower corner on the USB-C side.
  2. Put a strip of Kapton over each cell’s protection board.
  3. Lay both cells into the bay behind the spacer, flat, one on top of the other (the bay is two cells high), the end with the protection board and the wires towards the board. Put a strip of foam tape on top, so that the lid holds the cells without rattling.

The way of the cell wires has not been tried on a real light. If it does not fit, report it (section 16).

12.12 Close the lid

  1. Put the lid on: the end with the slot for the split ring is the tail. It sits in a small step around the tray.
  2. The pads push back. Press the lid down firmly with one hand and start the four M1.6 × 4 screws with the other, two at the head and two at the tail. Start all four, then tighten them in turn. Snug only: the threads are in aluminium and strip easily.

You should see: the lid flat on the tray, no gap, no wire pinched in the joint.

12.13 Test every button through its cap

  1. Unlock the light: 4 clicks on ●, ring green × 3.
  2. Click ●. You should see: the LED lights at Low. Click ›: brighter (Medium). Click ‹ twice: Low, then Moon. Click ●: off.
  3. Every cap should move a hair (the free play) and then click. No cap may stay down, and the light must not switch on by itself when you put it on the table or turn it over.
  4. Push S2 to SAFE and lock the light again (4 clicks, red × 3).

If a button does not work or feels wrong, see section 15 (caps).

12.14 Split ring

Thread a split ring or a lanyard through the slot in the tail.

13. Step 5 — First use

Plug in the USB cable and charge the light until the ring is steady green. Then:

13.1 Flashlight mode

13.2 Laser check

Rear view

Render, the laser side (+Y), head on the right. At the slide switch S2: SAFE towards the head, ARM towards the tail.

With the light off, click ●, then click and hold ●: the laser is on while you hold. The ring is steady red. The slide switch S2 in the side wall must be armed: knob pushed towards the tail (ARM). With the knob towards the head (SAFE) the laser cannot come on, whatever the software does: the switch cuts the laser’s supply in hardware (LAS-2). The laser stops after 60 s, above 60 °C, below 3.2 V and in lockout.

Check it once with the safety glasses on and the light pointed at a wall (unlock first: 4 clicks, green × 3): knob towards the head → no green dot; knob towards the tail → the dot appears. If the laser comes on with the knob towards the head, your switch works the other way round, and SAFE and ARM on the body are wrong. Do not use the light as it is, and report it (section 16).

13.3 Presenter mode

In presenter mode FlashKa is a Bluetooth keyboard that turns slides. The laser stays the pointer.

Enter it: hold ‹ and › together for 2 seconds. The ring blinks magenta twice and then breathes cyan, slowly: the light waits for a computer. The main LED cannot be switched on in presenter mode.

What the buttons do (the key set “Page keys”, the default):

You press Key sent
› click next slide: Page Down (key set “arrows”: Right arrow)
‹ click previous slide: Page Up (key set “arrows”: Left arrow)
› hold 0.8 s start the show: F5 (sent once)
‹ hold 0.8 s end the show: Esc (sent once)
● click black screen on or off: B
● hold laser while you hold (S2 on ARM)

Every key goes out once, as a quick press and release, so holding a button never makes the computer repeat it. Keys are sent only while a computer is connected (ring off). While the ring breathes cyan, presses are dropped.

13.4 First pairing (untested on real systems)

Pairing works only in presenter mode. The light uses a pairing method without a PIN (“Just Works”): the computer asks you to confirm. When the computer is connected, the ring blinks cyan twice and goes off. The steps below come from the documentation of each system. Nobody has tried them with a real FlashKa. If your screen differs, trust your system and tell the project.

System Steps Note
Windows 11, Windows 10 (1803 or newer) Settings → Bluetooth & devices → Add device → Bluetooth → “FlashKa-XXXX” (keyboard icon) older Windows 10 cannot pair
macOS System Settings → Bluetooth → “FlashKa-XXXX” → Connect close the Keyboard Setup Assistant if it opens
Android 6 or newer Settings → Connected devices → Pair new device → “FlashKa-XXXX” → Pair  
iPhone, iPad (iOS 9 or newer) Settings → Bluetooth → “FlashKa-XXXX” (Other devices) → Pair the on-screen keyboard hides while the light is connected
Linux (BlueZ, kernel 3.19 or newer) bluetoothctl: scan on, pair <addr>, trust <addr>, connect <addr>  

The light remembers up to 4 computers; a fifth replaces the one paired longest ago. After the first pairing, entering presenter mode is enough: the computer reconnects by itself and the ring blinks cyan twice.

13.5 Keys for your program

Which keys suit which program has not been tested. Choose the key set in the app (section 14).

Program Key set Note
PowerPoint (Windows, Mac), LibreOffice Impress Page keys (default) B is the black screen, Esc ends the show
PDF viewers Page keys (default)  
Keynote, Google Slides arrows (Right / Left) on a Mac, F5 does not start a show: start it on the computer
A program that ignores Page Up and Page Down arrows  

F5 starts a show in Windows and Linux programs only. If the slides do not move, try the other key set.

13.6 Leaving presenter mode, and forgetting computers

Presenter mode ends when:

Presenter mode keeps the radio on, about 20 mA (an estimate, not measured), which is about 30 to 40 hours from a full battery.

Forget all paired computers: hold ‹ and › together for 10 seconds. The ring blinks white × 3. On the way the light changes mode at 2 seconds (ring magenta × 2), as for any 2-second hold: from flashlight mode it enters presenter mode and stays there, ready to pair a new computer; from presenter mode it leaves. Also remove “FlashKa” from the Bluetooth list of each computer, otherwise that computer keeps trying the old key.

14. The app

On a computer (Windows, Mac, Linux, ChromeOS with Bluetooth): open app/flashka-app.html in Chrome or Edge. On a phone the page must come from a web address (https). The project publishes it at https://dompka.github.io/LuxLibre/flashka/flashka-app.html. Open that address in Chrome on Android, or in the free Bluefy browser on an iPhone or iPad. You can also put the app folder on a web site of your own (free on GitHub Pages, about 10 minutes, step by step in docs/web_apps.md, section 4).

The light listens for the app only in short Bluetooth windows: while it is on, for 2 minutes after it was switched off, after a triple click, or while USB is connected. So switch it on (or triple-click it) before you tap Connect. The app cannot connect while presenter mode is on: a light has one Bluetooth connection at a time.

What the app shows and does (the picture below shows the pages):

The web pages

Screenshots of the web pages in demo mode, not of a real light. Left: the light controls and the profiles. Middle: the Presenter card (dark theme). Right: the firmware installer.

15. Troubleshooting

Power, charging and the ring

What you see What to do
Nothing at all when you click Charge it (USB). The ring breathes red while charging.
USB does not charge The charger pauses above 45 °C and below 0 °C, and while the LED runs above 500 mA. Check the cable.
A short red flash when you click ● Locked: four clicks unlock it (green × 3).
Five fast red blinks Battery empty: charge it. (It also means that presenter mode ended because the battery fell below 3.20 V.)
One red blink The light refused a request: turbo when too hot, the laser when not allowed, switch-on with an empty battery, presenter mode in lockout or below 3.20 V.
› or ‹ do nothing Normal while the light is off or locked. They step the levels while the light is on, and turn slides in presenter mode.
The ring flickers red for a moment when the light starts Normal: the boot message runs over that pin.
A very short press on › or ‹ switches the light on Known: from deep sleep a very short press counts as ●. Hold a little longer when you wake the light.
Light gets dimmer by itself Normal: turbo time over, or temperature or battery protection.

What the ring shows (the complete table is in Appendix A, section A.5):

Ring Meaning
red, slow breathing / green, steady USB connected: charging / charge complete
red × 3 / green × 3 lockout on / off
green, yellow or red for 2 s after switch-on battery above 50 % / 20–50 % / below 20 %
red blink every 4 s while the light is on battery below 10 %
blue × 2 Bluetooth window opened (● 3 clicks while off)
blue double blink every 3 s flashlight mode: Bluetooth window open, nobody connected
cyan (dim), steady flashlight mode: the app is connected
cyan × 3 “Identify” from the app
magenta × 2 presenter mode entered or left
cyan, breathing presenter mode: waiting for the computer
cyan twice, then off presenter mode: computer connected
short white blip a presenter key was sent
white × 3 paired computers forgotten
red, steady laser on
one red blink request refused
five fast red blinks battery empty

Presenter mode and pairing

What you see What to do
The computer does not list FlashKa The ring must breathe cyan (waiting). If not, enter presenter mode (‹ and › together, 2 s). One red blink means the light refused: it is locked, or the battery is below 3.20 V. Bluetooth must be on in the computer.
Pairing fails, or the computer says it cannot connect Remove FlashKa from the computer’s Bluetooth list and pair again. Do this after every firmware installation too: the installation makes the light forget its computers, but the computer still holds the old key.
A computer cannot pair at all A computer that only supports old (“legacy”) pairing cannot pair: Windows 10 before 1803 and Android before 6. The light uses only LE Secure Connections.
Paired, but the keys do nothing The ring must be off (connected). Cyan breathing means no computer is connected, and keys are dropped. Click into the slide window first so that it has the keyboard focus. Try the other key set in the app.
F5 does not start the show F5 starts a show in Windows and Linux programs only. On a Mac start the show on the computer.
The app cannot connect One connection at a time: the app cannot connect while presenter mode is on. Leave presenter mode first (‹ and › together, 2 s). A paired computer in range may also hold the link for up to 10 s; wait, or switch off its Bluetooth.
Presenter mode ended by itself The idle time ran out (30 minutes by default), the battery fell below 3.20 V, or USB was plugged in.
A computer should forget the light Hold ‹ and › together for 10 s (ring white × 3) and remove FlashKa in the computer’s list.

Laser, installer and app

What you see What to do
Laser does not come on S2 must be armed (knob towards the tail). The gesture is click, then click-and-hold from off (● hold in presenter mode). It stops above 60 °C, below 3.2 V and after 60 s, and never works in lockout.
Installer: no port Data cable, other USB port (section 10).
Installer: connection fails Hold a button while plugging in (section 10).
Installer: “The firmware inside this page is damaged” Get the page again (a changed file fails the check).
App: “the button has priority” Wait 3 seconds after pressing a button, then try again.
App finds no flashlight Bluetooth is off to save power: switch the light on, or click ● three times (ring blue × 2), then Connect. It also finds nothing in presenter mode.

Buttons and caps (the new mechanics)

What you see What to do
A cap sticks or does not come back up Take it out and test it on its own: it must fall through its bore by its own weight (section 8). Look for epoxy in the tube bore or on the cap, a burr, or a printed bore that is too tight. Use a tube from the spare kit, or the resin cap.
A button feels soft or loose Every cap has 0.30 mm of free play by design; it moves that far before the switch clicks. If the button feels spongy: are both pads stuck on the bosses and the lid screws snug? The ‹ button is the known weak spot of the hold-down (chapter 13, section 13.4.5). Report how it feels.
A cap presses its switch by itself (the light switches on, the ring lights) The free play is gone. Open the lid. Look for glue on a cap, a tube that sits too high, a cap that is stuck, or a pad that is thicker than 1.0 mm.
The ring is dim or uneven Not known yet: nobody has seen a real ring. The light passes through 8.2 mm of printed resin. Report what you see (chapter 13, section 13.9, item 9).
The lid does not close flat The board is not flat on its ledges, a wire is under it, the antenna spacer is not down, or a pad is too thick.
The caps fell out The tray was turned over. Drop them in again from inside (section 12.7).

16. Where to read more

Tell the project what you find. No FlashKa had been built when this guide was written, so every result helps: what you ordered and what the shops said, what worked, what you measured, what went wrong. Open a Build report in the issue tracker of the LuxLibre repository (github.com/DomPka/LuxLibre).

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