Wow! I started work on this post back in August, while I was working on the War Doctor cosplay. Between that costume, my trip to Rwanda, and the holidays, I took a break from working on this costume. Since the first of the year I've been trying to get the eye mechanics working. I've come a LONG way on the eye mechanics, which is what the servos will be driving, so I'll need to do a few posts in order to catch up.
I started by testing the servos that I'll be using in the head to move the eyes and eyelids. I've selected the Arduino controller (specifically the Uno) to initially set up and drive the servos. It requires the least amount of support hardware, and if this were the only electronics in the system, it would be my final choice. However, one of the advantages to the Raspberry Pi is that it can do many, fairly sophisticated tasks. I won't use it initially because of the additional hardware it needs as a development station. But, if I start doing the audio and video controls I'm thinking about, I'll bring out the Raspberry Pi.
I used jumper wires to run a servo directly from the Arduino. That gave me a sense of the power of the servo (I had one available from another project), but also pointed out problems using the same power for the servo as the digital control electronics.
So I bought a daughter card for the Arduino (called a shield by Arduino developers) that is meant to control servos. I had to bring out the soldering station to finish assembling that card. I was also able to grab a few power adapters I have lying around (I collect wall warts and power supplies from a lot of my electronic projects and gadgets). I programmed the servo controls to give me periodic motion, and viola - servo driven electro-mechanical testing platform for eye motion.
Okay, to clarify my off-handed remarks, I've been working in electronic design and assembly since before the micro-computer revolution. I put together my first computer from components when the first micro-controllers were available to the public and used it to drive a robot (circa 1974). My graduate work was in Electrical and Computer Engineering, and my first engineering job was designing, installing, and programming embedded micro-computers to replace high precision analog temperature controls. I have a LOT of electronic experience along with the tools and components lying about to just do these sort of projects. So yeah, when I say "viola - it worked", I realize I'm not giving it the same level of detail discussion as my efforts to sew a pattern. Frankly, it takes me a lot more effort to figure out how to use the sewing machine with a zig-zag seam. Yeah, this is a brag, but my intent is to explain why I'm probably not giving a lot of details on the electronics. I just didn't think about it until it was done.
Anyway, my next entry will be about my stumbling around coming up with working eye mechanics. That is a much more humbling experience.