Bluepy-scratch-link is Scratch-link implemented on bluepy as a small python script. As of October 2019, Scratch-link is a software module which connects Scratch and Bluetooth devices such as micro:bit. However, it works only on Windows and MacOS, and cannot connect Scratch and micro:bit on Linux.

Bluepy-scratch-link allows Linux PCs to connect Scratch and micro:bit. It uses Linux Bluetooth protocol stack Bluez and its python interfaces pybluez to handle Bluetooth, and bluepy to handle Bluetooth Low Energy, or BLE, connections with micro:bit. It is confirmed that bluepy-scratch-link connects Scratch 3.0 and a micro:bit, and a Lego Mindstorms EV3.

This is a minimal implementation to support micro:bit and Lego Mindstorms EV3. It may work with other devices but these are untested. Some Scratch-link features are not implemented.

Bluepy-scratch-link requires python version 3.6 and later to use websockets. If your system has python older than version 3.6, install newer version. If your Linux system has explicit command names python3 and pip3 for python version 3, use them in the instructions below.

Confirmed Environments

The instructions below was confirmed with following devices and distros. Trial with other distros and feed-backs will be appreciated.

The bluepy-scratch-link was confirmed with following devices:

micro:bit by @kawasaki
Lego Mindstorm EV3: by @chrisglencross

The bluepy-scratch-link was confirmed with following Linux distros:

Arch Linux by @kawasaki
elementary OS 5.0 Juno by @kawasaki
Raspbian by @chirsglencross

The bluepy-scratch-link was confirmed with following browsers:

FireFox by @kawasaki
Chromium by @kawasaki

Installation

Prepare Bluetooth/BLE controller.

Confirm that your Linux PC has a Bluetooth controller with BLE support. Bluetooth 4.0 controller supports BLE. If your PC does not have it, need to plug USB Bluetooth 4.0 adapter.

Install required packages.

Ubuntu
$ sudo apt install bluez libbluetooth-dev libnss3-tools libcap2-bin
Arch
$ sudo pacman -S bluez bluez-utils nss libcap

Install python modules.

$ sudo pip install bluepy pybluez websockets
Or if your system has python3 command,
$ sudo pip3 install bluepy pybluez websockets

Get bluepy-scratch-link.

Example below installs bluepy-scratch-link under your home directory.
```
$ cd ~
$ git clone https://github.com/kawasaki/bluepy-scratch-link.git
```

Prepare web server certificate.

Scratch-link requires local Secure WebSocket server with certificate. Run a script to generate the certificate file and corresponding key file. Be sure to run it as the user to run the web browser for Scratch so that the script can add the generated certificate to FireFox or Chrome.

$ cd ~/bluepy-scratch-link
$ ./gencert.sh
Generating a RSA private key
..................................................+++++
.....................................................................................+++++
writing new private key to 'scratch-device-manager.key'
-----
Generated certificate: scratch-device-manager.cer
Generated key: scratch-device-manager.key
Added certificate to FireFox NSS DB: /home/shin/.mozilla/firefox/XXXX.default
Added certificate to Chrome

Set bluepy-helper capability

./setcap.sh
Set up bluepy-helper capability to allow use by normal users
/usr/lib/python3.8/site-packages/bluepy-1.3.0-py3.8.egg/bluepy/bluepy-helper = cap_net_admin,cap_net_raw+eip

If using a micro:bit, install Scratch-link hex on your device.
- Download and unzip the micro:bit Scratch Hex file.
- Flash the micro:bit over USB with the Scratch .Hex File, you will see the five character name of the micro:bit scroll across the screen such as 'zo9ev'.

Usage

For Lego Mindstorms EV3, pair your Linux PC to the EV3 brick.

First, turn on the EV3 and ensure Bluetooth is enabled.

Then, pair using your Linux desktop's the Bluetooth settings.

If using Gnome:
- Settings -> Bluetooth
- Click on the EV3 device name
- Accept the connection on EV3 brick
- Enter a matching PIN on EV3 brick and Linux PC. '1234' is the value Scratch suggests.
- Confirm EV3 status is "Disconnected" in Bluetooth settings
With a Raspberry Pi default Raspbian desktop, click the Bluetooth logo in the top right of the screen and Add Device. Then follow the Gnome instructions. You will be warned that the Raspberry Pi does not know how to talk to this device; that is not a problem.

Alternatively you can perform pairing from the command-line:
```
$ bluetoothctl

[bluetooth]# power on
Changing power on succeeded

[bluetooth]# pairable on
Changing pairable on succeeded

[bluetooth]# agent KeyboardOnly
Agent registered

[bluetooth]# devices
...
Device 00:16:53:53:D3:19 EV3
...

[bluetooth]# pair 00:16:53:53:D3:19
Attempting to pair with 00:16:53:53:D3:19

# Confirm pairing on the EV3 display, set PIN to 1234

Request PIN code
[agent] Enter PIN code: 1234
[CHG] Device 00:16:53:53:D3:19 Connected: yes
[CHG] Device 00:16:53:53:D3:19 Paired: yes
Pairing successful

[bluetooth]# quit
```

Start scratch-link python script.

$ cd ~/bluepy-scratch-link
$ ./scratch_link.py
Or if your system has python3 command,
$ python3 ./scratch_link.py

Connect scratch to micro:bit or Lego Mindstorms:
- Open FireFox or Chrome and access Scratch 3.0
- Select the "Add Extension" button
- Select micro:bit or Lego Mindstorms EV3 extension and follow the prompts to connect
- Build your project with the extension blocks

In Case You Fail to Connect

If Scratch says "Make sure you have Scratch Link installed" but you are sure that scratch-link python script is running, check that Firefox or Chrome allows local server certificate.
- Open Firefox or Chrome and access https://device-manager.scratch.mit.edu:20110/. You will see a security risk warning.
- In Firefox: Click "Advanced" and click "Accept Risk and Continue".
- In Chrome: type the special bypass keyword thisisunsafe.
- Immediately, you will see "Failed to open a WebSocket connection". This is expected.
If device scan fails, check systemd bluetooth service status.
```
systemctl status bluetooth.service
```
- If the service is not working, refer guide of your distro to set it up.
- If the service is working, also check that /etc/bluetooth/main.conf sets AutoEnable=true.
If scratch_link.py says "failed to connect to BT device: [Errno 13] Permission denied", make sure to pair the bluetooth device to your PC before connecting to Scratch.