Sense HAT Web Emulator

This is a web emulator for Sense HAT applications. You may use it to preview your Sense HAT applications locally, thus testing they work correctly before you push them to your Raspberry Pi.

The web emulator runs your application using your local Node.js but if you have nodemon installed, it will use nodemon instead; this way you can have the emulator running and reloading the browser whenever you save your code files.

When you start the web emulator, it will automatically open a browser tab for you. The SPA running in the browser communicates with your application via sockets.

Installation

Add sense-hat-web-emu as a development dependency of your project with

npm install sense-hat-web-emu --save-dev

or

yarn add sense-hat-web-emu --dev

Usage

The web emulator basically provides a replacement for the sense-joystick and sense-hat-leds npm packages.

Most probably your Sense HAT application looks something like this:

const senseJoystick = require('sense-joystick')
const senseLeds = require('sense-hat-led')

// your application code which uses senseJoystick and senseLeds

Ideally, in order to use the web emulator you would modularize your code so that your application's entry point receives senseJoytick and senseLeds as parameters. This not only makes it easier to use the web emulator, it also makes your application easier to test.

Your entry file would look something like this:

module.exports = (senseJoystick, senseLeds) => {
  // your application code here
}

Here's an example of what an application's entry file could look like:

module.exports = (senseJoystick, senseLeds) => {
  senseJoystick.getJoystick().then((joystick) => {
    const _ = [0, 0, 0] // black color
    const R = [255, 0, 0] // red color
    
    joystick.on('press', val => {
      if (val === 'click') {
        senseLeds.setPixels([
          _, _, _, _, _, _, _, _,
          _, R, R, _, _, R, R, _,
          R, R, R, R, R, R, R, R,
          R, R, R, R, R, R, R, R,
          _, R, R, R, R, R, R, _,
          _, _, R, R, R, R, _, _,
          _, _, _, R, R, _, _, _,
          _, _, _, _, _, _, _, _
        ])
      }      
    })
  })
}

When running the Sense HAT web emulator, it will automatically inject the emulator versions of senseJoystick and senseLeds into your applications entry point.

Now you can add a script in your package.json file

"scripts": {
  "webemu": "webemu start --file ./path/to/file.js"
}

And you'd either run it with:

npm run webemu

or

yarn webemu

Alternatively, if you don't have a package.json file or don't want to add a script to it, you can also run:

./node_modules/.bin/webemu start --file ./src/test-app.js

Options

These are the option flags you can provide to the web emulator:

Flag	Description	Default value	Required
file	Relative path to your application's entry file	-	Yes
launch	Specify whether to launch the browser when the web emulator starts	False	No
port	Specify the port where the web emulator will start	3000	No
watch	Specify whether to start the web emulator in watch mode (requires nodemon)	False	No

Examples:

./node_modules/.bin/webemu start --file ./src/test-app.js --port 4000

./node_modules/.bin/webemu start --file ./src/test-app.js --launch --watch

Controls

Once your Sense HAT application is running, use your keyboard to control the Sense HAT joystick. Controls are as follows:

• UP: Up arrow ↑
• RIGHT: Right arrow →
• DOWN: Down arrow ↓
• LEFT: Left arrow ←
• CLICK: Enter key ↩

Demo

Check out this running demo!

The commands for the demo application are the following:

• Pressing Up arrow ↑ displays the message hello world! one letter at a time
• Pressing Right arrow → scrolls the message hello world!
• Pressing Down arrow ↓ flips the 8x8 LED matrix vertically
• Pressing Left arrow ← loads an 8x8 pixel image of a space invader
• Pressing Enter key displays the next shape in the collection (heart️ ❤️ / smiley 😀 / earth 🌎 / star ⭐️ / check ✔️)

Here's the source code for this Sense HAT application.

Disclaimer

The web emulator runs your Sense HAT Node application on the server side and communicates with the browser through sockets. Because of the asynchronous nature of this communication, an application written using the synchronous version of senseLeds methods will not work correctly. If you're willing to use the web emulator and it's not imperative for you to use synchronous methods, I'd recommend using their async version. Otherwise, I'm truly sorry and also accepting contributions to work around this limitation.

Documentation

• Documentation for sense-hat-led
• Documentation for sense-joystick

Thanks

Thank you for trying the Sense HAT web emulator!

Your feedback is very welcome, and your contributions even more so!