NDS E-Z channel end cap / end outlet (UPC: 0 52063 81813 9)
0.5" x 3.73 plastic sewing machine bobbin
0.5" x 0.5 cylindrical magnet
approximately 150' of 34 gauge enameled copper wire
0.75" x 4" wooden dowel
24" 19 gauge steel wire
0.5 oz quick set epoxy glue
0.125 x 8 brass rod
2-liter plastic soda bottle
1) To wrap the spring: Take the 0.75" x 4" wooden dowel and make a mark 1 from its end. Starting at the mark and working towards the closest end, make approximately 7 turns with the 19-gauge wire. The last coil on the spring should be located at the end of the rod. Leave a small section of excess wire at each end.
2) Cut the brass rod into two 4 lengths. Wrap one of the excess ends of the 19-gauge wire around the end of one of the brass rods. Using a small amount of epoxy, permanently attach the coiled spring to the rod and let dry.
3) When the rod is secured to the spring, attach the magnet to the opposite end of the rod, again using epoxy.
4) Bend one coil on the spring so that it is parallel to the surface of the plastic base. Now, with a large amount of epoxy, secure the spring to the center of the base. Once the epoxy has set, gently bend the spring so that the rod is
5) Use a knife or razor blade to cut the 2-liter bottle laterally 2.75 from the bottom.
6) Using the power drill as a threading mechanism, make approximately 1,000 coils (or until the bobbin is full) with the 34-gauge enameled copper wire around the 0.5 x .75 sewing bobbin. Be sure to leave at least 3 of spare wire on each end of the coil as leads.
7) Drill a 0.125 diameter hole in the center of the 2-litre bottle cap. Drill another 0.0625 diameter hole, in the cap, offset slightly from the first hole to thread the leads through.
8) Attach the sewing bobbin/inductance coil onto the end of the second copper rod using epoxy. Try to have as little of the rod in the center of the bobbin as possible (a small amount of tape works well to hold the rod out of the bobbin).
9) Feed the free ends of the copper wire through the 0.0625 hole at the top of the bottle cap. Insert the free end of the coil/rod assembly into the 0.125 hole in the cap. Carefully screw the cap onto the bottle. Slide the bottle shell over the NDS E-Z channel end cap / end outlet there should be a snug fit. Adjust the rod/coil assembly so that a small gap of about 0.0625 separates the magnet from the coil. When the spacing is correct, epoxy the brass rod to the cap (from the outside).
10) Using sandpaper, gently strip off the thin coating of enamel from the ends of the wires. Connect the two wire ends to the amplifier/analog to digital converter as indicated in its respective instruction set. Connect the output of the a-d converter to the serial port of a PC.