Update 9/17/2013: Thanks to everyone who voted for this project in the Arduino contest (I was one of ten "second prize" winners)! If you want to try this project with an addressable LED strip instead of an analog strip, check out the Rainbow Jar project (also an Arduino contest winner).
This is my take on a combination of two classic projects: RGB LED control with an Arduino, and an Infinity Mirror. It's an RGB LED infinity mirror that lets you toggle between an adjustable-speed color-fade mode and a direct-control mode where you individually set the red, green, and blue LED brightness levels. The primary inspiration for this particular project comes from this infinity mirror Instructable and Adafruit's RGB LED Strip tutorial, but there are many more quality resources out there on both projects.
I've done my best to gear this project towards newbies by providing an exact list of materials I used and the exact procedure that I followed. One recurring theme I've noticed in comment sections for other infinity mirrors is a lack of links to specific parts (e.g. exactly what type of LEDs or LED strips were used, what power supply, where to buy the mirrors, the enclosure...). Clearly, if you know what you're doing and want to spend more (or less) money to design a slightly different mirror, you can adjust your materials as needed, use a different Arduino board, etc. You can skip the Arduino entirely and make a pretty simple, cheap infinity mirror if you want (just search Instructables for "infinity mirror" and you'll find a few), or go crazy and spend hundreds if not thousands of dollars (search YouTube for "infinity mirror table" and you'll get the idea).
So, on to the materials list. Remember that this is an exact list of parts that I used, but I gradually cobbled together the supplies for this project over a long period of time. I didn't sit down, compare vendors (e.g. Adafruit vs. Sparkfun) and find the absolute cheapest way to build this. So, feel free to shop around to bring down the cost (and post links in the comments if you find a better/cheaper version of a certain part!). Quantities are just 1 (one) unless otherwise noted, prices are rounded to the nearest dollar as of September 2013.
- Arduino UNO R3 with mini breadboard and jumper wires. I have the Getting Started with Arduino Kit from Maker Shed ($65).
- (Optional): Arduino/breadboard holder. The Maker Shed kit didn't come with one - I 3D printed this cool minimalist design I found on Thingiverse.
- 1 meter RGB LED strip ($25). This is an analog strip, which means you can only control the color of the whole strip at once. SparkFun also carries a digital RGB LED strip which has individually addressable LEDs (if you wanted to send pulses of light down the strip one LED at a time, or have some other pattern), but it's more expensive ($45) and you'll need completely different Arduino code. Both strips can be cut to length to fit your mirror.
- Four 10K potentiometers ($1 each).
- Three N-channel MOSFETs ($1 each).
- SPDT power switch ($1.50).
- 22 AWG hookup wire (black), 100 feet ($8). This is only required if you pref to color-code your V+ and ground connections with red and black respectively. Otherwise you can just use the multi-colored jumper wires that come with most Arduino kits. 100 feet is also WAY more than you'll need for this project, but you can never have too much hookup wire! You can get a smaller 25' roll from SparkFun.
- 22 AWG hookup wire (red), 100 feet ($8). Same note as above, with smaller roll here.
- Barrel jack breadboard adapter ($1).
- 12V/5A DC power supply ($25). This is a big place to potentially save money. The RGB LED strip I used requires 12V, and according to the datasheet, draws 60mA for every 3-LED segment (the smallest unit the strip can be cut into). So at 60 LEDs for the whole strip, that's an absolute maximum of 1.2A at full brightness. I had a 12V charger laying around from some old long-forgotten device, but it was only rated at 0.5A and couldn't light the whole strip. So, I went ahead and bought a beefy supply because I figured it would be useful for future projects anyway. Adafruit and SparkFun both carry smaller, cheaper 12V supplies (1A and 600mA respectively) that might suit your needs just fine depending on the size of your mirror and how many LEDs it will use. You could also scavenge something like an old laptop charger, but be sure to check the output voltage and current specs (usually printed on the label).
Important: there are three main parts that need to fit together to build this: the regular mirror, the frame, and the one-way mirror. First, it's easiest if you can find a cardboard/paper mache lid and a regular mirror that will fit snugly inside it - the parts I bought didn't fit together perfectly, so I had to use a workaround (see Step 6). Second, cutting acrylic can be a pain depending on the tools you have available, so plan accordingly (see Steps 9 and 10). There's also an important consideration regarding the LED strip, which can't be cut to any length - it has to be cut in multiples of 3-LED segments, which are just shy of 2" long - so you want the inside perimeter of your mirror frame to be a multiple of that length. So, I'll link to the parts I used to build my mirror, but you can still follow these directions to build a mirror of a different size or shape.
- 9" diameter circular mirror. I bought this kit of 7 mirrors ($14) with the intent of also making some smaller infinity mirrors.
- Kit of 8", 9", and 10" diameter round paper mache boxes ($9). Important - I bought these hoping that the 9" diameter mirror would fit snugly inside either the 9" lid or the box itself (and because I couldn't find individual boxes for sale on Amazon). It didn't. The 9" lid was just too small, and the 10" box was too big. So, I made it work by cutting out the top of the 9" lid, and just using the rim. This will make sense if you skip ahead and look at the pictures in Step 6. Point being, ideally you should use a mirror that fits snugly inside a paper mache lid or box.
- 1/8" thick 12"x12" sheet of clear cast acrylic (plexiglass). Available on Amazon ($8) and McMaster-Carr ($9). Acrylic is super easy to cut if you have access to a laser cutter. I don't, so I tried using a jigsaw (Step 9) and a score-and-snap method (Step 10). Both worked reasonably well but resulted in some jagged edges, and in hindsight would have worked much better for a rectangular mirror instead of a round one. If you want to build a slightly smaller mirror, McMaster sells pre-cut 6" diameter circles. I didn't shop around much for larger pre-cut circles but you might be able to find them.
- Mirrored window tint. I ordered this stuff from Amazon ($27) but you can easily find this in hardware stores. Probably hard to find in small quantities, so plan on having plenty left over.
- Black paint. I picked up a can of generic black spray paint ($3) at A.C. Moore.
- Optional: if you want to get really fancy, you might be able to order a custom-sized one way mirror, instead of putting mirrored window tint onto a piece of plexiglass. This will probably give you a higher optical quality in your final product, but I didn't look into it.
- Soldering iron. I have this variable temperature one from SparkFun ($45). You might be able to get away without one, depending on how your LED strip arrives. The SparkFun product page says "You will need to solder on your own wires.", but my strip arrived with all four wires already soldered on. Even so, pushing the ends of the (stranded) wires into a breadboard can be a pain, so I recommend soldering on small segments of solid-core wire to make that easier.
- Lead-free solder ($8).
- Wire strippers ($5), if you don't already have a pair that can strip 22 AWG. Again, you can squeeze by without these if necessary, but I'm betting most people reading this have wire strippers.
- Mini needle nose pliers ($2) if, like me, you're clumsy and hate handling tiny breadboard components with your fingers.
- Power drill (see Step 6 - you can probably just get away with a sharp knife)
- Super glue
- Electrical tape