What methods can be used to bulk erase a lot of floppies? I dont have one of those nice big electromagnets, and was wondering if anything else to hand could be used. I presume 2 seconds in a microwave with a load to prevent sparking is too risky, though I should try one.
Cant think of anything else that causes a strong enough mag field... any ideas?
On 11 Jul 2005 15:45:50 -0700, snipped-for-privacy@meeow.co.uk wroth:
If you have a burned out large diameter "woofer", disassemble it to get to the magnet structure. You can leave the iron pieces attached, just remove the cone and its support "basket". After you degauss your floppies, you can use it as the worlds strongest refrigerator magnet.
Magnets do indeed destroy data, but if that's all he wants to do a bonfire is even better. If he wants to re-use the floppies he would be better off with something that creates an alternating magnetic field.
I thought that's what those small rare earth neo hard drive magnets are for! I've have seen people dent fridges trying to get those off.
As long as the flux concentrating steel rings/disk are still there on large speaker magnets, they can have an impressive flux field in the circular gap.
might sitting the flop on a piece of metal foil result in enough magentism? In an oven with a load to prevent arcing. I'll try it anyway, and let you know how many floppy drive heads I trashed.
The frequency is irrelevant. The point is to have a strong enough magnetic field to line up all of the little magnetic thingies in the media, and then turn them all around on the next half-cycle.
A permanent magnet will line up all the little thingies, but then you've got a magnet bias that could introduce confounding factors when re-using the media.
Anyway, with the AC field (hey, there's a usage of AC that we didn't consider in the "Tastes Great-Less Filling" ACDC thing!), just twirl the magnet fast enough that it can sweep the field over the media once or twice.
Then, the secret is, slowly move the moving magnet ( or half a transformer, or whatever) away from the media, and as the alternating field gets weaker and weaker, reversing fewer and fewer thingies, until on the average, there's no residual magnetism in the media.
It's the same principle with CRT degaussers, but they use a PTC thermistor in series with the coil. Press the degausser button on your monitor - see the pretty patterns? And how they decay? That's the principle that ends up with negligible residual magnetization. I know there's a whole nother jargon here, but, come on! :-)
Which brings up the question, what is the optimal frequency? With an electromagnet you get 50/60 Hz unless you go to a lot of effort to get another frequency - and it works well - but with a motor/magnet it's easy to pick a frequency.
It has to be a low frequency to penetrate the magnetic layer. Also the magnet would have to be mounted so the north and south poles would alternate. A magnet from a speaker would have to be mounted from its edge to work.
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Link to my "Computers for disabled Veterans" project website deleted
after threats were telephoned to my church.
(Go back and read what I replied to. The prev. post said there was no magnetic field inside a microwave oven)
I don't have advanced equipment here but lets assume that the earths field is about 0.5G in the middle of my kitchen. Outdoors within 20 miles of here, it is 0.495G or so, so I think this is accurate enough what I'm about to do.
I hold the compass in the middle of the kitchen and note the direction of the pointer.
Next I bring a small magnet towards the compass from what it indicates is the east while rotating the magnet to find the orientation that causes the greatest deflection.
When I obtain a 45 degree deflection, the magnet is making as much field at the compass as the horz. component of the earths field. I measure this distance and find it to be just about 4.25 inches.
We know that where I am the earths field is just about 0.5G and dipped by about 60 degrees. This means that the magnet at 4.25 inches is producing a field of:
0.5G * cos(60) = 0.25G
Next I place the compass inside a Panasonic microwave on a non-magnetic book such that the compass is about 1.5 inches above the bottom of the oven, and nearly centered. Again I observe the compass pointer and introduce the magnet from its east until I obtain a 45 degree deflection. I measure this distance. I comes out to be just about 2 inches.
The magnet I'm using is 0.25 inches in its largest direction so I feel safe in using the small dipole estimate. Therefor I calculate the horz component of the field inside the oven is:
0.25G * (4.25/2)^3 = 2.4G
Since this is the Horz component it represents a minimum for the field value. It is a lot more than "no magnetic field" but as I pointed out not one that will be good as a bulk eraser.
Actually you don't need a changing field if you are allowed to change the location of the magnetic media, but that is too much of a quibble.
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