In the previous log, i described the general concept, and my vision of the user interface. Today, i will present a few design choices that i made for this project. My goal is to keep costs low, and use open hardware as much as possible, as well as free software. Furthermore, i will try to use standard stuff as much as possible. Not necessarily for the node itself, but for the devices controlled by the system. Indeed, i do not want to have a system that is only able to control very specific, rare, complex and expensive pieces of equipement.

If the system has to control a light, it should be able to control a standard light socket. Same for fans : a house fan should be controllable. In order to acomplish this, i will be controlling mains suply for these devices. I will thus use relays to activate or deactivate standard power plugs. The idea behind this is that if one needs to change a device, any other similar device should be a drop in replacement. Of course, power usage will have to be considered, but for now i'm planing on controlling low power devices such as lights and fans, so it is well below the power rating of my relays and wires.

I tend to prefer developping my own systems for most things, but in this case, it should be servicable by a user with no electronics knowledge. Of course, if the node itself is fryed, it would have to be replaced. But no programming for the user :)

This design choice may however reduce the amount of functionalities that could be implemented. As an example, for fans, if i were to use DC fans, i could drive it with PWM and have a fine speed tuning. With a mains AC fan, i can have it on or off. However, the PWM fan would require a more expensive system, and would be more complex to replace if needs be.