section 01 a website

Guide to WiFi on PicoRuby/R2P2

14:00, May 4 2024

This is a preview of what’s to come in my RubyKaigi 2024 talk, and also a guide for people who want to try what I will be talking/have talked at RubyKaigi 2024.

Links to relevant repositories are below:

Please note that I am omitting explanations of what PicoRuby and R2P2 are. Please go check the official repository for those.

Building PC version R2P2

You can build R2P2 that runs on PC with MRUBY_CONFIG=r2p2-bin option. This is used to check functionality that doesn’t depend on devices. I used this to test the cryptography implementation.

The following will get you from a full-scratch Ubuntu installation to building the PC version R2P2. Your mileage may vary but you will most likely start after installing the latest Ruby version.

# build latest ruby
sudo apt install git build-essential autoconf patch rustc libssl-dev libyaml-dev libreadline6-dev zlib1g-dev libgmp-dev libncurses5-dev libffi-dev libgdbm6 libgdbm-dev libdb-dev uuid-dev
git clone ~/.rbenv
echo 'eval "$(~/.rbenv/bin/rbenv init - bash)"' >> ~/.bashrc
git clone "$(rbenv root)"/plugins/ruby-build
rbenv install -l
rbenv install 3.3.1
rbenv global 3.3.1

# install gcc-arm-none-eabi
sudo apt install gcc-arm-none-eabi

# clone PicoRuby, then build PC version R2P2
git clone --recursive
MRUBY_CONFIG=r2p2-bin rake

# run PC version R2P2

Building R2P2

Preparing the build environment


Connect to R2P2

Load .uf2 file

Connect your Pico W while pressing the BOOTSEL button. This will give you a storage device named RPI-RP2. Drag and drop the .uf2 file that contains the R2P2 executable (either the one downloaded from GitHub releases or the one you’ve built). After the file has been copied, a storage device named R2P2 will come up on your system. This means that you’re ready to connect with the following steps.

On a Linux

On a Mac

…because that’s like Hello World in IoT!

The code written in the rest of the article will be run under irb. There is an option to run code by putting app.rb/app.mrb inside the Pico W’s storage but here we’re doing it on irb.

CYW43.init "JP"
pin =

Note that in a Pico without the WiFi chip the LED pin is not under the CYW43439 chip so it runs like:

led =, GPIO::OUT)

Connect to WiFi

To try this out, you will have to checkout sylph01/R2P2 wlan branch. The submodule points to a commit under sylph01/picoruby’s wlan branch, so after checking out wlan branch, go inside lib/picoruby, set remote to sylph01/picoruby, then check out the wlan branch.

After R2P2 and lib/picoruby points to the wlan branch, build R2P2 with BOARD=pico_w rake. If this is your first time building and cloning Mbed TLS, some Mbed TLS functions might cause an error saying they lack references or something. Retry the same command again, and the build will complete. After the build completes, you will get the .uf2 file under build/ directory, so copy that onto your Pico W.

Here are some stuff you can try out:

# Connect to WiFi
CYW43.connect_blocking('your_aps_ssid', 'password', CYW43::Auth::WPA2_MIXED_PSK)

# Resolve DNS names
require 'net'

require 'net'
client ='')
r = client.get('/')