Well, I'm proposing to my girlfriend. I'm usually pretty creative when it comes to birthdays and such, so I've got to be REASONABLY creative here. I've got an idea that has been bouncing around in my head for a few years.
You know those long thin sticks on a base that folks use for putting their rings on while they do dishes? If not, here's an artsy version:http://www.etsy.com/listing/95136436/ring-holder-dish-maple-leaf-shaped-hand?ref=&sref=
I had the idea about 10 years ago to put an LED at the top so that there would be a visual cue that the ring was left on it. At the time, the hobbyist market wasn't so hot, and it was expensive to get boards made and the LEDs I wanted were too expensive and blah blah blah. My idea at the time was to have the (likely conductive) ring complete a circuit. Well, this would work, but later I realized that wouldn't be so hot for the ring itself, being prone to current corrosion. At the time I was offhandedly thinking that I would build in some cathodic protection and pray.
Now, I'm not sure at all that that would be practical or even clever.
Back to the point at hand, I've been talking about this project with my girlfriend for a while now, and she's aware that it's a pet 'someday' idea. As a goofy proposal idea, I think it would be cool to build it up, make it WORK for SURE, then when showing it to her, give her the ring to test it with.
Without TOO much commentary on how lame this idea is compared to the time you proposed from a hot air balloon over the arctic sea, I'd like to get some thoughts on how to go about this.
#1: IR. Hollow spike (gotta be hollow to run the LED to the top) with an IR emitter inside that's lined up with a quite small hole that is JUST proud of the base. This would mean that even a very low profile ring would get hit. Just to the side of that emitter, a receiver that would wait for the light to be reflected back. Obviously I'd have to firewall them inside the pole, but otherwise it might just work.
#2: Lasers. See all of that above? Ya, that, except that this base would have a raised rim around the edge. The rim would be big enough to house a laser diode that would be aimed at a photo transistor inside the pole. Interrupt the laser? Boom. To make it last more than 3 minutes on a 9v, I would have the laser pulse once every few seconds for a few milliseconds.
#3: I dunno? I've mucked around with super high sensitivity capacitance measurements, but not on an Arduino, and not for this budget.
#4: Weight. I can built a scale sensitive enough that will do the trick but it will be expensive and picky. I can hack a cheap one digital scale, but that's getting silly.
How would you do it? The main requirements:
1. LED goes at the top of the pole. Constraint: pole must be hollow.
2. It must be battery powered. This doesn't mean that the prototype has to run for more than an hour, but still...
3. The pole has to be thin enough to allow a size 6 ring to slide all the way down to whatever sense method is chosen.
4. It has to be able to detect a ring that might not fit ENTIRELY snugly to the bottom of the base because of its shape, but should also be able to detect a quite small band. (can't only detect the bottom .5mm but can't start the detection 3mm up)
5. It has to fit in a base no bigger than say 10" diameter. That's on the outside, and I don't really see that as being a problem, I'm just saying.
6. The solution has to be build-able without paying a fortune. I can get PCBs made in my shop, pick and place for the heck of it, reflow and work all the way down to 0402. I more mean I don't have a commercial lathe and CNC mill.
I hope you all can help