|HomeNet - A Wireless Network of Household Appliances|
Developing the HomeNet system was a successful project that demonstrates the feasibility of using centralized PC control to interact with appliances in a household environment. Our key accomplishments are:
· Creating a wireless network of appliances
· Creating a successful protocol for communication
· Successfully controlling the network from a GUI interface on a PC
· Long Battery Life
· Using existing, everyday appliances
· Low Cost
The HomeNet project was successful in meeting the basic requirements it set out. A wireless network of household appliances was created that could effectively interact with a central controller and the normal household environment. HomeNet also shows that convenient control of everyday appliances can be accomplished through the use of a PC, which could eventually be extended to include a mobile device such as a PDA. This shows that with some additional work to develop more types of appliance nodes, the HomeNet system would be an effective solution for home automation and control.
Low cost was also design goal for the HomeNet system. By purchasing the parts individually, a single node on the HomeNet network costs $22.25. However, based on the price breakdown shown at www.digikey.com, we estimate that costs could be cut approximately 40% merely by placing larger orders. We anticipate that by using more cost effective packaging and by placing larger orders, a single node could be assembled for around $10 - $12.
Another design goal was to maximize the battery life of the network nodes. Electrical components were chosen to minimize the amount of power that they would consume while in operation. Specific steps were taken to further reduce power consumption by using large resistors, where possible, to reduce current draw and by turning off transmitters when they were not needed. By implementing these steps, we were able to get a very long battery life for the nodes. Throughout the entire year, only a single 9V battery was needed to power a single node, and the battery was still operating by the end of the project. We estimate that the battery operated continuously for approximately 50 hrs and its output voltage dropped by 1.2 V.
Additional steps can be taken to further improve battery life. In the current design, the biggest consumer of battery power is the microcontroller itself. In the future, we would like to put the microcontroller to sleep when it is not needed to further save power. This could be implemented by having the master node issue a command to a node telling it to go to sleep for a specified time interval. When sleeping, the microcontroller would shut off all its functions except for an internal counter that would wake up the microcontroller after the specified time has elapsed. If implemented properly, the node microcontroller could remain asleep roughly 90% of the time, only waking up to listen for a new message then returning to sleep. This would further extend battery life to make the system even more cost effective.
The area that needs the most improvement is the range of the network. During initial testing, straight antennas made from normal wire appeared to be adequate for that range we required. However as we built up the system, adding more complexity to the nodes and increasing the number of nodes, the range for the RF communication suffered. In the end we were only able to reliably transmit a complete round trip message over a few feet. To make HomeNet a viable product, this range needs to be increased to the order of 50 -100ft so that the majority of the rooms of an average house could be included within the network. We believe that the RF transmitters and receivers used in the HomeNet design are capable of meeting this requirement, but some work is needed to find the optimal antenna and configuration to improve range.