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domenica 8 marzo 2015

A very simple internet of things system to control lights and other stuff

In these days i've worked on how to create a system that allows me to turn on and off lights or appliances at home with minimal cost and complexity, and there it is:

Each node (ESP-01 ESP8266) with nodemcu firmware and the init.lua script from esp8266 folder of my repository has two outputs and can control two appliances.
A node has commands to retrieve name , unique identifier and current state, and to set the state, all that happens via UDP packet.

At first i tried, especially for discovery purposes to use UDP broadcast packets, but it seems that the module has some bug that makes the reception of broadcasts very unreliable, so at last i resorted to try to send a command to query status for each ip address specified in the subnet, like for, it would be to

The server which runs on an ARM board like a raspberry or a beaglebone takes care of the authentication of the clients from the internet ( the ESP8266 modules have no authentication , they rely on the safety of the network, so avoid passwords like "password" or "0123456789" ).

When first started the server creates a self signed certificate to use with HTTPS and a random password, then when the user connects to the webserver from a local ip address a qrcode is displayed to configure the android application.

The QR Code contains the public ip address , the port , the password and the sha1 fingerprint of the certificate, so that even if it is self-signed, it can be verified by the application to prevent man in the middle attacks.

The servers also takes care of enforcing state on the nodes, especially when a packet is lost or when the node for some reason loses power, at each discovery the state is compared and if not equal it will be resent again until the node status matches.

That's it, with barely 200 lines of python and a trivial android app you can safely control your house from where you want.

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