Hipmunk Bathroom Status Indicator Sign

I work at Hipmunk, an awesome hotel/flight search site based in San Francisco. To give a bit of background, until our subtenants move out, our current office has a single bathroom for more than 10 employees and nobody can see the bathroom door to see if it's in use, so there's a bit of lock contention.

The obvious solution is an airplane style bathroom sign.  So I made one at Techshop San Francisco, using only the laser cutter.

Step 1: Front Design

The design is based on this style of airplane bathroom sign, which I believe is standard on an Airbus A330.  Since we have a cute Hipmunk mascot, I had to include him.  And while two Hipmunks on the sign tilted each direction might be ultra cute, Hipmunk was founded by the same guy who made Reddit, and so the Reddit alien was an obvious choice for the second figure.

Using the picture as a reference, I traced the sink and mirror pattern from the original sign and the Hipmunk mascot, then found a vector version of the Reddit alien and assembled them all together into a 15"x8" rounded rectangle.

Step 2: Case Design

I don't really know anything about bending acrylic, but I have glued some before.  For this sign, I just used a box made out of layers of 1/8 inch acrylic to create a space to fit all the LEDs and have the light bounce around a bit.  In the final version the layers are so, from front to back:

* white border around front to hold next layer
* single-side frosted clear (translucent acrylic causes the pattern to be too blurry), with opaque white border on three sides to hold this layer in place
* white with the pattern cut out
* mirror with the pattern cut out (this layer is not entirely necessary, since it only serves to reduce the light leakage through the layer before it)
* translucent white to diffuse the LED light, I believe it's 60% transmission
* about 8 layers forming the wall of the sign (one of these layers holds captive nuts for the screws that hold the back on)
* mirror acrylic
* white spacer layer
* white layer with wall-mounting holes

it may be possible to sand the sides flat, but I like the rough layered look, so I left it as-is.

The layers are almost all glued together with acrylic glue, except for a gap before the last mirror layer, which is so the back of the sign can be removed.

Step 3: Electronics

The circuit is about as basic as possible. There are no arduinos here.  Just a relay with a resistor, a magnetic door switch, and LEDs.

* relay: 653-G6RN-1-DC5
* 100 ohm resistors: 293-110-RC
* green LEDs: 941-C503BGCNCY0C0792
* red LEDs: 941-C503BRCNCW0Z0AA2 
* copper wire
* magnetic door sensor (self adhesive!)
* stereo cable, 1/4 inch stereo plugs and sockets, and project box from radioshack
* 5V, 2.5A DC power adapter I found in my room

The box contains a relay and a resistor to limit current through the door switch, it then switches the 5V power supply to one of the two conductors in the audio cable.  I used the copper shield of the audio cable as a ground and the return path for the current from the sign.

I used a piece of acrylic with lots of holes lasered out to hold all my LEDs (about 11 of each color).  The copper wire acts like a bus bar powering the LEDs, one for each color, then a common ground connection.

Step 4: Assembly Test

After cutting out all the layers, I assembled a strip of LEDs (actually used some acrylic perfboard I made to fit in the sign), and tried it without gluing anything to see how well it worked.

Note that there is not really enough diffusion with just the top strip of LEDs.  I added a strip of frosted acrylic over the strip of LEDs inside the sign to diffuse the light.  I also made cutouts of the hipmunk and reddit alien from 60% transparent white acrylic that I placed under the frosted cover layer to further increase the light diffusion.

If I made another sign I would use more LEDs and diffuse the light a lot more.

Step 5: Installation

I installed two screws into the wall spaced 8" apart, then hung the sign above this sort of doorway/staircase thing.  The wire runs into the "server closet" under the stairs, into the relay box, which then has a cable that runs to the bathroom door around the corner.

It works pretty well since people would already leave the bathroom door open when not in use.  I got lucky with estimating the wire lengths so I didn't end up having to splice any wires together.

Besides the reportedly amazing productivity benefits, it was a a fun project and, as always, the laser cutters are like making things on ez-mode.