Introduction: Compass

About: Will Bosworth, developing projects for HowToons @ SquidLabs.

Always getting lost? Build this compass out of a CD and a small magnet.

Step 1: Parts Layout

a compact disc (hopefully used / useless)
a small magnet
the outer case of a 50 pack of cd's. (can substitute anything that will hold water and a floating cd, a cd-case looks nice)
some hot glue
some water

Step 2: Glue Magnet to CD

Glue the magnet pretty much anywhere on the cd*, with a pole facing radially outwards. If the magnet's pole does not face radially outward the compass will be decieving.

To find the poles, place the magnet in the presence of other magnetic objects. The magnets will attach to each other along their poles if they have enough mechanical freedom to.

  • Depending on magnet size, glue-ing too far away from the cd's center will tip the cd (think center of mass). But, if the magnet is too close to the center the torque arm length about the center will not allow for the compass to spin / function properly.

Step 3: Find North

lay the cd+magnet into a bowl of water and watch is align itself with north. The attached video shows the compass aligning itself (it's a kind of boring video)



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    15 Discussions

    Sorry, where is the video?

    I would like to build a compass with a CD but my design is a little different. I would like your opinion if it would work. I would oppose two ring magnets on a dowel, the top ring magnet would be glued to the CD, so then the CD would levitate with the dowel down the center. Then I would take some metal wire touching the top magnet and extend it out to the end of the CD. I may have to counter the balance with maybe a copper wire on the other side. Do you think this would work?

    I suddenly got an idea! *rips t-shirt* Oh man... Now all I need is a sheet of PET...


    11 years ago

    So simple yet what a stroke of genius! I'll definetly be using this when doing compass instruction with my Scouts in a few weeks! A floating CD and a magnet is a lot more 21st century than the old "floating cork and magnetized sewing needle" trick. Thanks! Great idea!

    1 reply

     Hey, the needle and cork has been around for years! (But this version looks like it could work a little better because the floating component has more surface area).

    NICE. Gonna try this one tonight! --puts on MacGyver disguise--

    Really stupid question: how do you know which is the North face of the magnet?

    1 reply

    Not a stupid question.
    1) build it, if it points away from the sun around noon (assuming your in the northen hemisphere) you have the southern pole of the compas magnet pointing toward the north pole.
    2) if you want to get elaborate or just play with electro mag's check out this link... pay special attention the various "left hand rules" and how the wires are turned...

    At last! Something that old CDs can be used for! Tip: balance the weight of the magnet with a counterweight on the opposite edge of the disk to prevent tipping. A washer or two hot-glued to the disk will work nicely.

    Lovely simple Idea, the kids in my sunday school group are going to love making these! Pete

    We did this for a Cub Scout den project (pack 682 WA) this evening. We used a magnet from a Magnetix kit. We had a good discussion on compasses and magnetism. I had the magnet from a dismantled hard drive handy and we could see the repulsion/attraction from about 12”. The best part it got the scouts thinking; “What happens if you turn the magnet around?” and related questions and theories.

    I'm so putting one of these on the dash of my first car :)

    This is really cool! If you added a few vertical lines around the spindle lid this could even be accurate enough to take a bearing. I think I'll make one of these up and keep it hand for the coming apocalypse :)

    Simple and educational. Thanks.