Arduino stoplight web server

Step 13 Notes

Laser challenge

As stated in the intro, I would REALLY like my own laser cutter. In this particular project it probably wouldn't have been much use, although I would like to experiment with using a laser cutter with self-etched PCBs. There are, however tons of other projects I fantasize^* about doing if I had one. Just a few:

• Edge-lit Christmas cards.  Last year I made these cards and they were well received. With a laser cutter I would get a lot fancier with the window.  More importantly, I would like to experiment with etching the plastic itself with the cutter, allowing tremendously more complicated designs (and a less sore thumb) than I achieved with a push pin.
• Personalized Christmas ornament cards.  Another card idea is be personalized balsa wood cards that would have components to punch out and assemble into ornaments.  About a decade ago I sent out Christmas cards that included an origami crane as an ornament.  A picture of it on a friend's tree showed up on facebook last year, so I know such cards are treasured and kept.
• Personalized wooden air planes to give out to every child I know.
• Any custom shim, brace, filler or decorative part I need cut for any small project.
• Engrave any phone or other electronic device with important information and silly art.
• Make parts for a CNC device.
• Do any and many of the hundreds of projects on instructables and other sites that include "cut these pieces out with a laser cutter".
• Make my own enclosures for my projects that are exactly the right size.
• Make beautiful and useful things.
• Make beautiful and useless things.

^* often, when I probably should be sleeping

Bulb Brightness

The original choices offered by the stoplight vendor were 60 watt bulbs and 40 watt bulbs, with the latter being recommended for indoor use.  The people sitting near the light quickly discovered that even 40 watts was obnoxiously bright.  The reflectors are VERY efficient at directing the light outward.  We ended up replacing the bulbs with 20 watt appliance bulbs and the results are much nicer.  The light can still be seen well from anywhere in view, and the folks in the cubes under it no longer have to bring umbrellas for shade.

PCB vs protoboard

If you have the time, I strongly recommend having a PCB printed, with the earlier mentioned caveat about the fact that this layout is untested. The wiring to the protoboard is tedious. If you do get it printed, please let me know if there are any problems with the board layout in the zip file. (It has since been successfully printed by an instructables user.)

Optional Outlet

The original plan called for a fourth output to a wall outlet.  We had planned to use it to plug in a beacon or noise maker for "extra urgent, everyone drop everything, the world is going to end" type events.  In the end we did not want to mar the light by drilling holes in it, and decided that making the red light flash during such an event was sufficient.  The fourth output is there in our light and it can be triggered to make a "click" sound, but if you don't plan to have this feature you can just leave it out and save yourself the cost of a relay.

If you DO include an outlet as a fourth output, it is important to note that you should not plug in any device drawing more than 430 watts (3.9 amps).  This is because the total draw (including all three lamps on) must not exceed 5 amps or the fuse will pop and you will have to open the light to reset it.  DO NOT consider leaving out the fuse because the relays are not rated for more than 5 amps.  Drawing more would be a fire hazard.

Other lights

There are a couple of other similar projects I've found:

• I used http://rockwellschrock.com/projects/traffic-light/ (which I found after I thought I had made up the idea) for some sanity checking.  This light requires a computer attached directly via USB to control it, but does have a more flexible control protocol. Someone unhappy with the options for controlling the light (which meet all our specific needs) might consider taking bits of his code and merging them with mine.  His design forgoes a complete arduino and just uses the atmega chip which makes it smaller and cheaper.  I used a full arduino because I needed to integrate with the Ethernet shield.
• Apparently github has a light, used to denote build status. I discovered this page after I had finished the project.  This implementation uses a separate board for each relay, via three sparkfun relay boards.  This approach adds to the cost and possibly the size, but doesn't require any additional circuitry. Since each of the relays are separate, there is probably more flexibility about placement in the light, since the relays can be distributed anywhere there is room.  This project is also notable that instead of being notified by an external service of what state it should be in, it acts as a client and polls a web server to see what color it should be.  His comments about having to make the arduino reset itself every once in a while to combat a memory leak introduced by using DHCP makes me glad I chose to use a static IP address.