Sunday, September 05, 2010

Towards the Networked Home

In the last few weeks I have been putting together the various tools I will need to make a distributed Home Monitoring Network. Previous posts have discussed most of the basics of this project, here I thought I'd summarise the project and what we are going to do with it over the next few months.

In essence, the network consists of several Arduino Slaves, all connected together on a simple wired serial network and communicating with a Master "Hub" device.

I'm doing this in conjunction with my friends at OpenEnergy with the intention of providing a demonstration system of what can be achieved with low cost hardware and a simple wired network. We are making the most use of open source hardware and software, and by keeping the system simple, we hope that it will be of interest to others. Later on, we might extend it to include some wireless nodes, but for now we want to keep the costs and complexity down.

Central to every node on our network is a small microcontroller board, based on the ATmega328 microcontroller, and firmware produced using the Arduino IDE. Keeping things compatible with Arduino hardware and firmware will ensure that others can try out our methods with minimum of fuss. At a bare minimum, our network could be used to connect an Arduino board to a laptop, so that it can be individually controlled over a few metres of cable by simple serial commands typed into a serial terminal emulator.

To extend the system beyond 1 board, some simple additional hardware is needed to ensure that only one Arduino Slave can access the network at a time. This involves fitting a 74AHC125 quad tristate buffer to each slave, such that only one will drive the network at a time. This device costs about 20p and is easy to add to an existing Arduino. The 74AHC125 and a 4 way screw terminal connector could be fitted to a protoshield board.

I've been programming my bootloader into new ATmega328 chips using another Arduino as a programmer, and in this way it keeps the cost of the Slave down. The basic Slave can be built for less than £5 which means that having several slaves on a network is still inexpensive.

Slaves send and receive data at 9600baud as simple comma separated variable (CSV) commands. The command set is compact, relatively easy to remember and can be typed from a serial terminal programme. The use of a CSV command means that commands can be readily interpreted using simple command interpreter code, and a low overall overhead to the application sketch. Additional commands are easy to write and can be added as the application needs them. Further details of the command set and application sketches will appear in a later post.

So with the basics of a wired network in place, it's time to start applying it to a real household application. In Snowdonia we worked on a monitoring and control system for a small solar pV installation, but at a planning meeting at the start of the weekend we discussed all the applications which could easily be handled with such a monitoring and control network. Here's a few suggestions in a non-exhaustive list for domestic and renewable energy applications:

1. Room by room, central heating controller
2. Gas consumption monitor
3. Whole house electricity monitor
4. Solar water heating controller
5. Solar Photovoltaic controller
6. Wind turbine controller
7. Battery Bank Management System
8. Generator controller
9. CHP controller
10. Greenhouse monitor/plant irrigation system

1 comment:

Alistair said...

Ken, I very like your low cost practical approach.

Do you have any plans or ideas for providing the user/household with some low cost wireless display node ?