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.
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.
Again you are right on. Probably none of them are even tin coated now. Tin is relatively speaking an expensive metal compared to steel. These days most cans have an organic polymer coating, or for some, like cans that contain pineapple or other acidic liquids, they are zinc coated. There is no tin (Sn) in a tin can.
I trimmed the ends off an blank steel PCI slot cover to fix my WallStreet IBM drive upgrade.
I used some non-descript piece of steel, origin unknown, from my project materials junk box, to shield my TravelStar. Worked beautifully, till the PMU board went in the WallStreet.
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---------------------------------------------------- William E. Briggs, P.Eng. Senior Instructor Department of Electrical and Computer Engineering University of New Brunswick Fredericton, N.B. mailto:[EMAIL PROTECTED]
Former Columnist and Contributing Editor, MacCentral The AppleScript Primer http://www.maccentral.com/columns/briggs.shtml mailto:[EMAIL PROTECTED]
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