At 11:33 AM -0800 22/12/03, Paul Nicholson wrote:Yes, you need a material that conducts the magnetic flux so it doesn't get to the magnetic reed switch.
Precisely. It's got to be a ferromagnetic material with a sufficiently high "permeability" to contain the flux so it doesn't reach the reed switch until you close the cover. The reed switch is in the bezel on the rhs of the screen, just about 1/3 to 1/2 the way up from the hinge. For those who don't know what a reed switch is, it's two flat reeds that have a very small gap between them that provides an open circuit until a magnet pulls one reed into contact with the other, closing the circuit and allowing current to flow. They are held in rigid position in a glass casing and can be broken if you are handling them. Once you crack the glass the reed switch is toast. We use them in our first year lab in the section on magnetism and I always tell the students that this is how laptops know to go to sleep when the cover is closed. They relate better to real world examples.
There is a magnet mounted on the right side of the screen. The reed switch is located in the bottom part, not far from the HD. If the reed switch were in the top half this wouldn't be a problem no matter what HD you put in there.
Reed switches are also commonly used in burglar alarms for door / window switches.
The magnets in the TravelStar drive are stronger than the ones in the original WallStreet drives, which necessitates the magnetic shielding. Brass, tin, and copper are not going to work as they have low values of µr (mu sub r). But nickel would work, you're just not likely to find a piece in the right shape. Three Canadian dimes might do it, but I'd stick with steel as you're more likely to find the right shape.
However I think what you are calling "tin" is really plated steel. Elemental tin is not magnetic. Tin cans aren't tin anymore, they are coated steel.
I think pretty much from the beginning that "tin" cans were tin coated steel. Their first large scale use was, IIRC, during the American Civil War.
The solution I use is somewhat simpler. I have the problem and didn't install any shielding. I just turn the computer around a little while tapping the shift key and it will wake up. -- Clark Martin Redwood City, CA, USA Macintosh / Internet Consulting
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