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 # bluepy-scratch-link
-Scratch-link implemented on bluepy
+
+Bluepy-scratch-link is [Scratch-link](https://github.com/LLK/scratch-link)
+implemented on bluepy as a small python script. As of October 2019, Scratch-link
+is a software module which connects [Scratch](https://scratch.mit.edu/) and
+Bluetooth devices such as [micro:bit](https://microbit.org/). 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](http://www.bluez.org/) and its python
+interface [bluepy](https://github.com/IanHarvey/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.
+
+This is a minimal implementation to support micro:bit. Some of Scratch-link
+features are not implemented. For example, Bluetooth (non-BLE) devices are not
+supported. BLE device support other than micro:bit is not confirmed.
+
+Bluepy-scratch-link is for python 3 and do not work for python 2. If your Linux
+system has explicit command names python3 and pip3, use them in the instructions
+below.
+
+The instructions below was confirmed with elementary OS 5.0 Juno which is
+based on Ubuntu 18.04 LTS and Arch Linux. Trial with other distros and
+feed-backs will be appreciated.
+
+Installation
+------------
+1. Prepare 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.
+
+2. Install Bluez package
+    ```sh
+    Ubuntu
+    $ sudo apt install bluez
+    Arch
+    $ sudo pacman -S bluez
+    ```
+
+3. Install python modules
+    ```sh
+    $ sudo pip install bluepy websockets
+    Or if your system has python3 command,
+    $ sudo pip3 install bluepy websockets
+    ```
+
+4. Get bluepy-scratch-link
+   Example below installs bluepy-scratch-link under your home directory.
+    ```sh
+    $ cd ~
+    $ git clone git@github.com:kawasaki/bluepy-scratch-link.git
+    ```
+
+5. Prepare web server certificate
+    Scratch-link requires local Secure WebSocket server with certificate.
+    Generate and prepare a PEM certificate file.
+    ```sh
+    $ cd ~/bluepy-scratch-link
+    $ openssl req -x509 -out scratch-device-manager.cer \
+    -keyout scratch-device-manager.key -newkey rsa:2048 -nodes -sha256 \
+    -subj '/CN=scratch-device-manager' -extensions EXT -config <( \
+    printf "[dn]\nCN=localhost\n[req]\ndistinguished_name = dn\n[EXT]\nsubjectAltName=DNS:localhost\nkeyUsage=digitalSignature\nextendedKeyUsage=serverAuth")
+    $ openssl pkcs12 -inkey scratch-device-manager.key \
+      -in scratch-device-manager.cer \
+      -name "Scratch Link & Scratch Device Manager" \
+      -passout pass:Scratch -export -out scratch-device-manager.pfx
+    $ grep -h ^ scratch-device-manager.cer scratch-device-manager.key \
+      | tr -d '\r' > scratch-device-manager.pem
+      ```
+
+6. Install Scratch-link hex in micro:bit
+    * Download and unzip the [micro:bit Scratch Hex file](https://downloads.scratch.mit.edu/microbit/scratch-microbit-1.1.0.hex.zip).
+    * 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
+-----
+1. Turn on Bluetooth Low Energy controller
+    ```sh
+    $ sudo btmgmt le on
+    $ sudo btmgmt power on
+    ```
+
+2. Start scratch-link python script
+    ```sh
+    $ cd ~/bluepy-scratch-link
+    $ sudo ./scratch_link.py
+    Or if your system has python3 command,
+    $ sudo python3 ./scratch_link.py
+    ```
+
+3. Start Firefox and allow local server certificate
+    * Open firefox and open [https://device-manager.scratch.mit.edu:20110/](https://device-manager.scratch.mit.edu:20110/). You will see security risk warning.
+    * Click "Advanced" and click "Accept Risk and Continue". Your will see
+      "Failed to open a WebSocket connection". This is expected.
+    * This action is required only the first time to access.
+    * Note: it is not known how to allow Chrome to accept self signed
+      certificate.
+
+4. Connect scratch to micro:bit
+    * Open [Scratch 3.0](https://scratch.mit.edu/)
+    * Select the "Add Extension" button
+    * Select micro:bit extension and follow the prompts to connect micro:bit
+    * Build your project with the extension blocks