I made a magnetic field detector. I used a small U shaped magnet transformer core and wound a coil on the bottom length. This was then mounted on a piece of one inch PVC plastic pipe. One red LED and one green led were then attached to the core. A opamp was used to amplify the signal from the core and drive the LEDs. Two 9 volt batteries were mounted in the pipe and the pipe was mounted in a 2 inch piece of PVC so it could be rotated with a electric motor. The result was a spinning pipe that pointed north and south. As it can be used at any angle I found that it indicated a null and the LEDs went out when the pipe was parallel to the dip angle of the earth's magnetic field. I'm not sure what to do with it. Any ideas?