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Monday, May 11th, 2009 10:59 pm
So, yeah, I decided I needed a crazy project to be working on to keep away the "my research is going nowhere" depression feedback loop. I just do better when I have a crazy project to be working on -- my alignment is quixotic good, after all.

The idea: a pair of sunglasses with circular lenses with polarized sheets that can be rotated to change the opacity. Done with brass gears. And a small servo to automate the rotation. And a light sensor so it can compensate for changes in illumination.

It's just within my very limited production capabilities, with 99% of my shop in storage. The frame I'll cut out by hand, using a jeweler's saw. Which will be a pain, but I've done more tedious things in the past and lived to tell of it. And it will be in keeping with the overall steampunky feel of the things.

After a series of tragicomic events, I got the circuit working tonight. It's a simple little astable 555 timer circuit, sending out a variable PWM signal to control the servo. It has a potentiometer in parallel with the photoresistor, so I can adjust the gain. (I have no idea how much regular adjustment will be annoying...) I'll also add a cut-out switch to the light sensor, so the rotation be directly controlled manually with the pot. Along with the overall power switch, that will make for 4 inputs to control my sunglasses, which seems like a reasonable UI to me. All this will probably mount along with the power source on my vest, with just the servo control leads going up to the glasses themselves.



Once I get some direct sunlight, I can work out roughly the range of motion I should see under normal conditions. That will let me decide on a gear ratio (it looks like getting a full 90 degrees rotation on the lenses won't be practical, but I can live with that), thus fixing the size of the gears, and I can finally finalize the frame design. Probably too late to order stuff for this weekend, sadly, but there is no real hurry. I just want it all done by Burning Man, natch.
Wednesday, May 13th, 2009 06:55 am (UTC)
Pretty much exactly the one here (http://www.geocities.com/bourbonstreet/3220/servobasics.html), but with a photoresistor from pin 7 to R2, and the resistor and capacitor values tweaked to use a 50K pot. Nothing very advanced at all, really. Anything more and I'd want to flee to the safety of a microcontroller. (Like, I wish I could easily add a microphone and have it pulse to maximum opacity for a second or two after a loud noise -- peril-sensitive sunglasses! But doing that in parallel with everything else in circuitry? Not going to happen.)