Thursday, November 20, 2008

Invention Idea #1

My kids go to school and (probably) never wash their hands. I imagine 90% of the colds I get started their path to my nose on some doorknob there. How can we sterilize children more effectively?

I thought about blasting them with ultraviolet, but that leaves them leathery and tough. Good for character but hard to chew. How about just blasting doorknobs (and the like) with UV? How would you mount such a light to reach all the crevices? Well, you could make the knob out of glass and mount the light inside.

But it turns out you need a minutes-long exposure to kill bacteria with UV. And glass blocks it anyway. And even if it didn't, it would still be shining out into the room and eyes of students.

However, I just recently came up with another solution: Ultrasound. So a kid grabs a knob and leaves germs behind. He lets go. A sensor notes this and gives a brief blast of ultrasound, dismembering any organics. The next kid grabs and she doesn't pick up the nasties.

Google says this works, but talks about being immersed in liquid. Maybe that can be worked around. Or a gel coating on the knob. Or fill the school with water and equip the kids with scuba gear.

Monday, November 17, 2008

Magic Smoke and Mirrors

The task is very simple. I have a solar tracker. I have a microcontroller that knows what direction the tracker should be pointing. I have a cordless drill that I've taken apart to do the actual work. So why is it taking me WEEKS AND WEEKS to get this working? I can't even turn the drill on yet, at least not without threat of releasing the magic smoke.

It should be extremely simple. Here is how a drill works.

OK, so it should be easy to just replace the human-operated switch with a microcontroller-operated one.

The microcontroller replaces the human and relay replaces the switch. It's a high-amp relay because on the very first magic smoke release test I found that the drill draws 20 amps (or more!). It's also a 15V battery, so I managed to remember the resistance of the motor as being .7 ohms which makes the V=IR math work out.

However, when I almost melted my entire apparatus on the second test I realized that the motor is only about .1 ohms. How on earth can I be feeding 15V to .1 ohms and only drawing 20 amps? Including a current-limiting resistor doesn't improve things much, since it just wastes a bunch of power getting really, really hot. After a little thought, I decided to actually look at the drill switch. I can't get it open, but I was able to confirm this much:

I don't know how, but that magic box is somehow limiting the current. One thing I can see in there is a transistor, which could definitely do the job....except it would have to be awfully high power to handle 20 amps. Or maybe it isn't? Maybe the 20 was transient and it normally feeds more like 2-3 amps? No idea. Which leads me to think maybe I need to give up and do something like this:

Which is stupid. If I knew how it worked, I could probably hook the microcontroller directly to the magic box and forego all my rubegoldbergian relay stuff (which should be a post on it's own...). It's also annoying that I know this can't be an unsolved problem. But I must not be thinking of the right keywords to find the solution.