New project – IoT mesh

Recently I started my new project with Internet of Things. My idea is to create mesh of sensors or some other devices connected to each other over the network. These devices should include some common sensors for monitoring temperature, humidity, barometric pressure, light and others. There also should be some logging devices for creating graphs from received data or monitoring network functionality. And finally I want to create some devices controlled over this network, like IoT enabled window blinds.

My basic design goals are:

• Reduce cost as possible
• World wide access
• Secure
• Reliable
• Easy to use
• Keep it simple
• 100% open source

MQTT

Basic building block for creating network of interconnected devices is communication protocol. There is already excellent protocol designed for IoT called MQTT, which meet all my requirements. It is designed to connect client devices over central server using publish/subscribe scheme. That means that every device send publish data into network tagged with topic. Other devices interested in some topic can subscribe to it and receive those data.

Central server is called broker. It is responsible for collecting messages from publishers and delivering them to subscribers. Broker can be also bridged to another broker. There is already open source implementation of MQTT broker mosquitto.

World wide access

Mosqiutto normally communicates in plaintext over TCP connection. It also can be configured to use SSL layer for encrypted data exchange. However, cheap sensors have not enough resources to use encrypted communication.

This problem seems to be solved by dedicating small MQTT broker in LAN secured by firewall and placed behind NAT. Clients in this LAN communicates with broker in plaintext. This broker then will be bridged to some central broker on the public Internet over SSL making secure connection. Whole network then should looks like this.

That's basic idea of my IoT network. Next time we will look at building simple MQTT device.