# What You Need

:::{sidebar} Aside: the name Arduino
:class: yodan

Arduino is a microcontroller board bundled with a development environment that makes
it easy to program. It was born in 2005 at a design school in Ivrea, Italy (the
Interaction Design Institute Ivrea), as a cheap board for students. Until then the
students had used a BASIC Stamp, at about 50 dollars each.

The name comes from a bar in Ivrea where some of the founders used to meet, the
"Bar di Re Arduino" (King Arduin's bar). King Arduin was a real person who became
King of Italy in 1002. So we are building an OS on a board named after a bar named
after a king.

Sources: Wikipedia, [Arduino](https://en.wikipedia.org/wiki/Arduino) and
[Arduin of Ivrea](https://en.wikipedia.org/wiki/Arduin_of_Ivrea)
:::

| Item | Qty | Notes |
|---|---|---|
| Arduino UNO R4 **WiFi** | 1 | The WiFi variant (with the LED matrix), not the Minima |
| USB-C cable | 1 | Must support data |
| A computer | 1 | Windows / macOS / Linux |

```{warning}
There are two UNO R4 variants; this book uses the **WiFi** one.
```

```{figure} ../_static/uno_r4_minima_vs_wifi.png
:name: fig-materials-minima-vs-wifi
:width: 90%

Left: Minima. Right: WiFi. Only the WiFi board has the 12×8 LED matrix (bottom right)
and the ESP32-S3 Wi-Fi module (the large square on the left).
Source: Arduino, product images on docs.arduino.cc
([UNO R4 Minima](https://github.com/arduino/docs-content/blob/dab66ecbd6ad52cd742da6c19c5b6330a7f2caae/content/hardware/uno/boards/uno-r4-minima/image.svg) / [UNO R4 WiFi](https://github.com/arduino/docs-content/blob/dab66ecbd6ad52cd742da6c19c5b6330a7f2caae/content/hardware/uno/boards/uno-r4-wifi/image.svg)), placed side by side and labelled.
[CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)
```

```{figure} ../_static/uno_r4_wifi_os.jpg
:name: fig-materials-uno-r4-wifi
:width: 80%

The Arduino UNO R4 WiFi. The 12×8 LED matrix at the lower right of the board
marks the WiFi variant (shown here displaying "OS")
```

## Where to buy the Arduino UNO R4 WiFi

:::{sidebar} Aside: why UNO?
:class: yodan

"Uno" is Italian for "one", chosen to mark a major redesign of the Arduino hardware
and software. The R4 came out in 2023 and moved from the 8-bit AVR (ATmega328P) of
R1 to R3 to the Arm Cortex-M4 microcontroller this book's OS runs on (Renesas RA4M1).

Source: Wikipedia, [Arduino Uno](https://en.wikipedia.org/wiki/Arduino_Uno)
:::

The part number is **ABX00087**. Prices include tax and are as of 2026-09-14.

| Store | Price | Notes |
|---|---|---|
| [Arduino Official Store](https://store.arduino.cc/products/uno-r4-wifi) | €30.50 | |
| [DigiKey (Japan)](https://www.digikey.jp/ja/products/detail/arduino/ABX00087/20371539) | ¥5,033 | |
| [RS Components (Japan)](https://jp.rs-online.com/web/p/arduino/2662937) | ¥5,173 | |
| [Akizuki Denshi](https://akizukidenshi.com/catalog/g/g118246/) | ¥4,850 | Japan |
| [Kyoritsu Eleshop](https://eleshop.jp/shop/g/gNBA313/) | ¥5,060 | Japan |
| [Marutsu](https://www.marutsu.co.jp/pc/i/2773981/) | ¥5,322 | Japan |
| [Sengoku Densho](https://www.sengoku.co.jp/mod/sgk_cart/detail.php?code=EEHD-6864) | ¥5,400 | Japan; also in the Akihabara and Osaka stores |
| [Switch Science](https://www.switch-science.com/products/9090) | ¥5,500 | Japan |
| [Amazon.co.jp](https://www.amazon.co.jp/dp/B0C8V88Z9D) | ¥5,639 | Price depends on the seller |

Look-alike **compatible boards** are also sold (especially on Amazon). The
sample code was tested on the genuine Arduino UNO R4 WiFi, so pick one whose
brand is Arduino and whose part number is ABX00087.

## Board pinout

Use this when wiring (the servos and potentiometer in Chapters 9 and 12, the
servo driver board in Chapter 13). The on-board **L LED** is `LED_BUILTIN`
(D13 / P102); serial `D0/RX` and `D1/TX` are P301 and P302.

```{figure} ../_static/uno_r4_wifi_pinout.png
:name: fig-uno-r4-wifi-pinout
:width: 100%

Arduino UNO R4 WiFi pinout.
Source: Arduino,
[ABX00087 Full Pinout](https://docs.arduino.cc/resources/pinouts/ABX00087-full-pinout.pdf)
(page 1, cropped to omit the legend).
[CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)
```

## Board block diagram

USB-C goes through analog switches to either the RA4M1 or the ESP32-S3, and
the LED matrix is wired directly to 11 pins of the RA4M1.

```{figure} ../_static/uno_r4_wifi_block_diagram.png
:name: fig-uno-r4-wifi-block-diagram
:width: 100%

Arduino UNO R4 WiFi block diagram.
Source: Arduino,
[ABX00087 Datasheet](https://docs.arduino.cc/resources/datasheets/ABX00087-datasheet.pdf),
"3 Block Diagram".
[CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)
```