Introduction: Bathroom Status Indicator Lights and Automatic Switch

This project uses proximity switches and relays to control a bank of indicator lights.  The lights convey the occupancy status of two bathrooms.

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

An assumption must be made to simplify the act of determining if the bathrooms are avaliable or unavailable.  This determination will be based on the condition of the door.  If a bathroom door is open, the bathroom is avaliable.  If a bathroom door is closed, the bathroom is unavailable.  The input I used for detecting the status of the door are inductive proximity switches.

Inductive proximityswitches 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

This box is located in the attic.  It receives the inputs from the proximity switches, and via relays, toggles the red/green light circuits and the - yet to be seen - door mounted fan.

The box contains two eight contact block relays and a 15 Amp breaker.

Step 3: Outputs - Lights and Fan

Once the relays are triggered from the closing of a door they break the green light hot lead, make the red light circuit, and - in the case of bathroom A - cut the power going to the door mounted exhaust fan.

Step 4: Enjoy

This is my first instructable; so, any advise is more than welcomed.  I have enjoyed this site and yall's projects for - so long - that I had to contribute.

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 - 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 - joe