From Nerdhaus

Contents 1 Project Summary 2 Protocol Requirements 3 Transmission Medium 4 Devices 4.1 Wall outlet 4.2 Light Switch 4.3 Button 5 Questions 6 Reference Material

Project Summary

To design a home automation protocol for controlling devices anywhere in a house. In contrast to X10, Insteon and UPB, our system will not use the power line for data transmission. The goal is not to design a system that can be used in existing construction, but rather to design a system that can be easily integrated into new construction. By not using the power line for data transmission, we can build a faster and more reliable protocol.

Protocol Requirements

• Each node on the network has a unique address
• Devices can be queried so that an outlet can respond with its on/off state
• A command can have parameters, for example to set an RGB light to a specific color

Transmission Medium

Typical house wiring uses a 3-conductor wire: a white wire for the neutral, black for the hot line, and an unshielded copper wire for the ground path. Wires used for a 3-way switch (where two switches control the same lights) have 4 conductors. We could require the installation of this 4-conductor wire to each outlet, and use the extra conductor as the data path, with the grounding wire as the return.

Devices

Wall outlet

A device the size of a standard wall outlet contains all the parts for receiving a signal and turning on/off the outlet. One possibility for powering the device is: the relay can draw power from the 120v line, and the transistor controlling the relay can be powered from the data line?

Light Switch

A light switch can be programmed with a different device's code, so it can turn on and off a specific module. It can also have a unique code which could be received by the server.

Button

A button is given a unique code, and transmits that code any time it is pressed. This is useful only when the system is being used along with a centralized controller, probably a computer, so that a macro would fire when the button is pressed.

Questions

• Can the device's circuitry be powered from the data line, the way 1-wire does?
• Can we get away with using a shared data line for each device, or do we need dedicated wires like ethernet does, where each device connects to a switch/hub. That would take far more wire, and would add significant cost.
• Is it possible that a camera connected to the system could transmit a picture over the network? Or is a better solution to plug in an actual ethernet wire to a camera, and just send commands to it over the smaller network.

Reference Material

• Ethernet - We can draw some inspiration from the old CSMA/CD shared medium Ethernet protocol
• 1-Wire - A communications protocol which can power devices and transmit data on one line
• DMX - A protocol used for controlling stage lighting