# 光 Hikari

A custom WS2812 LED badge powered by a [Seeed XIAO (BLE/RP2040/ESP32C3/...)](https://wiki.seeedstudio.com/SeeedStudio_XIAO_Series_Introduction/) and written in [TinyGo](https://tinygo.org).

The PCB hosts 20 RGB LEDs arranged in a **4 rows × 5 columns** grid behind a frosted 3D-printed diffuser. A single button cycles through lighting effects.


![Video 3](assets/videogif3.gif)


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## Hardware

| Component | Note |
|-----------|-----|
| Hikari PCB | in hardware/pcb folder |
| 3D printed files | in hardware/STL folder |
| Flathead screw 2.1x10 | 4x |
| 20 × WS2812 LEDs (4 rows × 5 cols) | D6 |
| Tactile button | D3 |
| Qwiic / StemmaQT connector | D4 & D5 (I²C) |
| Passive buffer | D7 |

---

## Effects

Each press of the button advances to the next effect. The sequence cycles endlessly.

| # | Name | Description |
|---|------|-------------|
| 1 | **Rainbow** | All 20 LEDs show the same colour; the hue cycles slowly through the full spectrum (~20 s per revolution) |
| 2 | **Row sweep** | One row lights up at a time and sweeps downward; the hue drifts continuously |
| 3 | **Column sweep** | One column lights up at a time and sweeps rightward |
| 4 | **Stars** | 8 LEDs at random positions fade in with a random colour then fade out; when a star dies a new one appears elsewhere |
| 5 | **Breathing** | All LEDs pulse with a triangular brightness envelope (~5 s per breath); the hue shifts slowly between cycles |
| 6 | **Rainbow rows** | Each row shows a different hue (90° apart on the colour wheel); all hues advance together |
| 7 | **Wave** | A bright column chases across the grid with a two-column fading trail |

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## Flash

```bash
tinygo flash -target=xiao-esp32c3 -stack-size=8KB .
```

Requires TinyGo ≥ 0.41 and [`tinygo.org/x/drivers`](https://github.com/tinygo-org/drivers) v0.35.

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## Build

### Step 1 — Bare PCB

The back side of the custom PCB. Footprints for the 20 WS2812 LEDs are arranged in the 4 × 5 grid. 

![Step 1 – bare PCB front](assets/step1.jpg)

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### Step 2 — Qwiic / StemmaQT connector

We'll start with the SMD Qwiic / StemmaQT connector since it's the trickiest to solder. It is not really needed, but a cool way to extend the board with sensors. Use the help of some flux if needed.

![Step 2 – qwiic stemmaqt](assets/step2.jpg)

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### Step 3 — Soldering the button

The tactile switch is soldered to its footprint on top of the board. Easier than the stemmaQT.

![Step 3 – soldering button](assets/step3.jpg)

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### Step 4 — PCB fully populated

All 20 LEDs and the button in place. The XIAO BLE/RP2040/ESP32C3/... plugs in on the left edge. It's the easier one to do, and the last one to be done since it goes over one LED.

![Step 4 – PCB fully populated](assets/step4.jpg)


**NOTE**: Make sure all the LEDs are correctly soldered since once we solder the board there's no way to fix the LED behind it.
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### Step 5 — PCB seated in the frame

The board drops into the back shell. The silkscreen on the rear shows the Go gopher pattern.

![Step 5 – PCB in frame](assets/step6.jpg)

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### Step 6 — 3D-printed back cover

The black back shell printed in PLA. The XIAO slides into the slot on the side for USB access. Use 4 screws on the holes.

![Step 6 – back cover](assets/step5.jpg)


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### Step 7 — Frosted diffuser panel

A white PLA diffuser snaps onto the front of the frame to spread the light evenly across the grid. You could print different models of the diffuser!

![Step 7 – diffuser panel](assets/step7.jpg)

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### Step 8 — Finished

Fully assembled and running. The diffuser softens each LED point into a smooth glow.

![Step 8 – finished, lit](assets/step8.jpg)

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## Showroom

![Video 1](assets/videogif1.gif)

![Video 2](assets/videogif2.gif)


## License

[MIT](LICENSE)