I can't see my overhead door from my house. Sometimes, my door likes to do things like open immediately after closing, or the remote button is accidentally pushed, and I have no idea my garage is open to the world. I wanted to make a highly visible indicator that would tell me the position of the door just by looking out my kitchen window.
There are commercially available devices that do this in a fancier way (sounds, wireless, etc), but I wanted to build it myself for a few bucks.
Step 1: Parts
1. A generic 12v 500mA wall plug,
2. Ideal Security SK619 magnetic switch (normally closed)
3. A standard automotive SPDT relay
4. LED marker light from Princess Auto.
Step 2: Circuit
I want the light to turn on immediately when the door begins to open. If I just wired the magnetic switch to the light in a direct on/off circuit, it would need to be positioned at the end of the door track, and the light would turn on only when the door is completely open. The relay is needed to change the circuit from Normally Closed to Normally Open.
Step 3: Installation
The magnet half is mounted to the very top of the sliding door. The switch half is mounted to the door frame with a ~1/2" gap between them. I used a multi-meter to test continuity to make sure the distance would work.
The Relay is mounted to a board above the door, and the wires run to a terminal block which is fed by the 12v power supply.
I used speaker wire because it was cheap, and I had it on hand.
The LED was installed above the man door. A 3/4" hole is drilled, and the rubber grommet installed. The LED is pushed into the grommet.
Step 4: Operation
When the door is closed, the magnetic switch is closed, and the relay is feeding terminal 87 (a dead end), and the light is off.
When the door is opened, even slightly, the magnetic switch is opened, and the relay switches to 87A and completes the circuit to the LED.
Now, the door position is immediately apparent.