smart-pinhole-workshop/exercises/receive_light/problem.md

A nodeschool workshop to learn how smart (iot) things work.

YES! We sense and emit light readings.

The readings will help us take better pictures. But we need to know what they are.

Let's create a `LightMeter UI` to view our readings in real time.

`LightMeter` is a web UI widget. It visualizes light readings.

This solution will run in the browser. So, we'll use `web sockets` to connect to the `MQTT` broker.

__Write a program to visualize our photoresistor readings.__

- Connect to the `test.mosquitto.org` MQTT broker
- Use the WebSocket port (8080) and the 'ws' protocol
- Subscribe to the **ciot/pinhole/<your-id>/light/value** MQTT topic
- Create a new `LightMeter.Widget` instance.
- Set the `LightMeter.Widget`'s light level every time a message is received.

## Unique ID for topic

As before, set an ID in the MQTT topic that's unique to your light sensor.

**Make sure you use the same ID as before!**

Set **ID=<(twitter-handle)>** when you run your program. Read `ID` in your program using `process.env.ID`.

## For this you will need

1. Get lightmeter from npm: `npm install lightmeter`

In this solution you will need to:

- `require` the `lightmeter` module
- Instantiate a `LightMeterWidget` i.e. `var widget = new LightMeter.Widget`
- `widget.setLightLevel` when a message arrives on the `mqtt` connection.

## Docs

- MQTT - https://github.com/mqttjs/MQTT.js
- Subscribe - https://github.com/mqttjs/MQTT.js#subscribe
- Events - connect - https://github.com/mqttjs/MQTT.js#event-connect
- Events - message - https://github.com/mqttjs/MQTT.js#event-message