Problem: Two single user bathrooms - in a dorm style house - are shared by multiple people, but the bathroom doors are not visible from the main hallway. This results in many failed trips down the hallway, only to find the one containing all of your toiletries or both (depending on what the need may be) are already occupied.
Solution: A centrally located visual indicator to convey the use status of the bathrooms.
Step 1: Inputs - Detecting Door Status
Inductive proximity switches sense objects by generating a magnetic field. When a metal object reaches a certain distance from the sensors head, it will open or close a circuit (depending on the model). By placing a screw in the door, the sensor can be triggered when the door is closed.
Step 2: Relays - Control Box
The box contains two eight contact block relays and a 15 Amp breaker.
Step 3: Outputs - Lights and Fan
Step 4: Enjoy
Most of the hardware in this project is industrial grade leftovers, and I realize they are a little overkill for this application. Please don't let that discourage you from a similar project; other cheaper but more-than-reliable-for-this-application hardware is available. It could easily be duplicated with security magnetic break switches and some simple relays.
I look forward to updating this project as the questions come in.
Community suggested updates to be made:
option -- move more hardware into the attic to make installation less visible - jemivallo
info -- top down diagram of physical layout - jemivallo
info -- more detailed part descriptions - eli2k
info -- wiring diagram - eli2k
info -- more details on my relation to the building - lemonie
info -- advantages and disadvantages of used input - lowercase
option -- other forms of input and their advantages and disadvantages
detecting door lock using microswitches - frollard
motion sensors - pH_
contact sensor working off a low voltage detection circuit - cornboy3
read sensor and magnet to detect door position - Jeffrey G C
info -- the fan's purpose - iambarney155
option -- labels for light box - zoltzerino
option -- adding inputs and hardware to check for hand washing - monkeytoes
use the water to makeup a low voltage detection circuit for water flow - seifpic
use a momentary switch - pie ninja
build a input into the soap dispenser - clickcolleen
http://www.youtube.com/watch?v=qTF9-j_y7zU - clickcolleen
option -- replace light box with hotel vacancy sign - static
option -- one light vs. two light system - xavtek
option -- allow the door status to be checked remotely via webserver - drsquirrel
http://www.instructables.com/id/Garage-Monitor-3001/ - joe