Automatic Light Switch

This project was a compulsory project that I had to do in my last year at my senior school and therefore it had two whole portfolios to go with it, I will not be putting these online however, I felt I should just give a quick summary of what it did, the idea behind it, and how it worked.
The project I chose to do was a new form of automated light switch that would, using a dual beam system, count the number of people going in and out of a room. It would then turn the lights on or off according to the number of people in the room. The idea was fairly simple and therefore I decided I would expand on it slightly. I decided that as well as this basic operation it should also:

· Fit into a standardised double din wall box housing.
· There should be no visible fixings (so the standard m3 screws would have to fix and then be hidden in some way.
· The housing should use capacitive touch sensitive buttons, which I had not worked with before.
· The switch should also be able to function in an entirely manual mode, with predefined mood lighting levels available as well.
· The switch should be able to output the information about room occupation numbers for security systems, fire evacuation systems, and hotel lobby systems.
· I also wanted to incorporate an LCD screen to display information.

The assembly drawing below shows the exploded cad view of the complete design:

The project used a rapid prototyped clip that acted as the backbone of the project while also clipping into the frame that was screwed into the back-box. This solved the problem of hiding screws. I computationally tested this for injection moulding and stress analysis before manufacture. It was also designed with all the required draft angles taken into account for mould manufacture.

I could not find any capacitive sensing buttons so I designed them and lathed them from steel and aluminium bar, I then tested them on a breadboard. The acrylic separator was clear allowing them to be backlit.

The system was based across two PCB's that sat one on top of the other; the bottom one contained the brains while the top had all of the connections for the LCD display and the buttons. A large heat sink took up much of the space on the bottom PCB for the voltage regulator part of the circuit.

I made a section of wall and doorframe to mount my project in and I recessed the back-box. The light gate was contained inside a single housing and used a reflector to make the beam system work.
The project worked although the clip could have been a little stronger in holding the panel in place. I was happy with the results of this project and got near full marks in it.