MadSci Network: Engineering |
You pretty well have the right idea, just need a little help in understanding the principles. Electronic watches today all run pretty much on crystals that oscillate (vibrate) at high frequencies by being excited by very small electrical currents. The electronics in the watch count the oscillations and use it to keep track of the time. (We sort of do this already when we use a calendar and count the rotations of the earth. Each rotation of the earth counts as one day. Imagine if the moon spun around the earth once every second. If we were fast and had a good memory like a computer, we could keep track of the time by counting how many times the moon went by. Every 60th time would be a minute, etc. That's how the clock in your computer works, by the way.) The beauty of the electronic watches is that they don't need much energy at all, so the batteries last for a long time. I have had them last 2 or more years, especially if you don't use the alarm or light. So, if you don't want to replace the battery ever, you could use the motion of your hand to generate electricity and charge up either a capacitor or rechargable battery to power your watch indefinitely. The imbalance wheel generates electricity on the same principle used to make electricity in your car. A shaft with a magnet on it rotates past a wire coil. Any time a magnetic field moves past a wire, it induces a current in the wire. Normally, if you just randomly move a generator shaft back and forth, the electricity you generate flows back and forth and you get a net effect of nothing. But if you keep the shaft from running backwards, and put an offcenter weight on it, every time you move it around the weight will want to fall to the lowest point and move the shaft in the allowed direction. A sudden burst of electricity in the nearby coil will charge the battery. (Imagine a bicycle resting upside down on it's seat and handlebars, and one of those headlight generators mounted to rub on the wheel. Now put a heavy weight at one point of the wheel within the spokes. If you were to move the bike by flipping it over onto its wheels, then laying it on its side, then on its back again, etc, the weight would turn the wheel at times, sometimes not. But everytime it did, the generator would put out a short burst of electricity. Now, imagine the bike miniaturized and strapped to your wrist.) Actually, I suspect this is done more electronically by allowing the shaft to turn in either direction and using diodes (sort of one way valves for electricity) to allow the current to be generated in only the desired direction.
Try the links in the MadSci Library for more information on Engineering.