Harucom boots directly into IRB (Interactive Ruby Shell) as soon as you power it on. Just connect a USB keyboard and a monitor to start programming in Ruby.

Prerequisites

To use Harucom, you need the following:

Harucom Board
A TV or monitor with HDMI input
An HDMI cable
A USB-C cable
A power adapter with USB-C

Harucom outputs video at 640x480px resolution. Most PC monitors support this, but some TVs may not. If the display does not work, check your TV’s manual.

Setup

Connect a monitor to the digital video connector on the Harucom Board
Connect a keyboard to the USB-A port
Connect power to the USB-C port
(If present) Turn on the power switch

When powered on, a console screen appears and IRB starts. If you see the following screen, startup is complete!

Harucom OS 0.0.0 (888888)
(c) 2026 Shunsuke Michii

Powered by PicoRuby 3.4.1 on RP2350

For detailed usage, visit https://harucom.org/

irb> ▊

Using IRB (Interactive Ruby)

Harucom starts the Interactive Ruby Shell (IRB) on boot. When you see the irb> prompt, you can type Ruby code and it will be executed immediately.

irb> puts "Hello Harucom"
Hello Harucom
=> nil
irb> 5 + 3
=> 8
irb> _ * 2
=> 16

Use _ to reference the last result.

Multi-line Input

Block syntax like def or if automatically enters multi-line input mode when you press Enter.

irb> def greet(name)
..     "Hello, #{name}!"
..   end
=> :greet

irb> greet("Harucom")
=> "Hello, Harucom!"

Blinking an LED

Let’s try lighting up the LED on the Harucom Board. Enter the following program to make the LED blink.

irb> led = GPIO.new(1, GPIO::OUT)
irb> loop do
..     led.write 1
..     sleep 1
..     led.write 0
..     sleep 1
..   end

To stop execution, press Ctrl-C.

Keyboard Shortcuts

Key	Action
`Enter`	Execute the entered code
`Ctrl-C`	Interrupt running code
`Backspace`	Delete a character
`→` / `↑` / `←` / `↓`	Move the cursor
`Home` / `End`	Jump to beginning / end of line
`PageUp` / `PageDown`	Page scroll

Editing Files with the Text Editor

Use the edit command to launch the text editor, where you can save and edit Ruby scripts as files.

irb> edit hello.rb

Editor Shortcuts

Key	Action
`Ctrl-S`	Save
`Ctrl-Q`	Quit
`Ctrl-Z`	Undo
`Ctrl-Y`	Redo
`→` / `↑` / `←` / `↓`	Move the cursor
`Home` / `End`	Jump to beginning / end of line
`PageUp` / `PageDown`	Page scroll

The editor displays the filename and position in the status bar. [+] is shown when there are unsaved changes.

Your First Program

Let’s create hello.rb using the editor.

irb> edit hello.rb

Enter the following code, save with Ctrl-S, and quit with Ctrl-Q.

Harucom has not only a text-based console screen mode but also a graphics mode that can display graphical content. P5 is a Processing-like drawing library built into Harucom.

require "p5"

p5 = P5.new

colors = [
  p5.color(255, 0, 0),
  p5.color(0, 255, 0),
  p5.color(0, 0, 255),
]

p5.background(0)

loop do
  p5.fill(colors[rand(3)])
  p5.circle(rand(p5.width), rand(p5.height), 10)
  p5.commit
  sleep_ms 100
end

Return to IRB and run it.

irb> run hello.rb

If lots of circles appear on the screen, it worked! Press Ctrl-C to stop execution.

If there is a problem with the program, an error will be displayed at runtime. Open the editor again to check if the content is correct.

Getting Started