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Step 4Make and Mount the Sensor Coil
The sensor coil is where the pulses are generated. As the "north-up" magnet passes the coil we get some electricity flowing in the "+" direction, then a transition to the opposite when the "north-down" magnet passes. So, we end up with a cycle of + and - oscillations at the speed of the spinning gear.
Cut a short section of the plastic pen or dowel. Wrap the magnet wire around it in a few layers to make a coil. You want your wrapping to be fairly orderly, so the first layer covers the bare cylinder before the next layer covers the first. I didn't count when I made mine, but expect a few hundred turns.
Use the Super glue to seal the coil so you can let go of it without the whole thing coming undone. (Tape helps here too.)
Now start thinking of how to shape your sheet metal/plastic into a bracket to hold the sensor. You want to suspend it close to the spinning magnets, so it hovers a few mm away. It must be secure, because you don't want any crashes here! I bent my aluminum into an L along its long side, so it would mount on a nearby motor-mount post.
Now drill 3 holes in the bracket:
1) A mounting hole to bolt the bracket to the motor-mount
2) A smaller hole on the other end where the coil lives. A wire-tie loops through this hole and cinches the coil to the bracket. (Note lack of glue, because we might have screwed-up the coil and it's no fun to un-glue things later!)
3) A hole in the middle so your cable can pass through the bracket.
Solder the wires from the coil onto the end of your unbalanced cable. This cable will carry the signal from the coil through the inside of the projector to the jack, which will be added to the rear panel. You will need to strip the painted insulation off of the ends of the magnet wire. Use a match to burn it off, or some fine sandpaper to lightly scratch it away. Remember to insulate it with electrical tape or tiny heat-shrink tubing.
Cut a short section of the plastic pen or dowel. Wrap the magnet wire around it in a few layers to make a coil. You want your wrapping to be fairly orderly, so the first layer covers the bare cylinder before the next layer covers the first. I didn't count when I made mine, but expect a few hundred turns.
Use the Super glue to seal the coil so you can let go of it without the whole thing coming undone. (Tape helps here too.)
Now start thinking of how to shape your sheet metal/plastic into a bracket to hold the sensor. You want to suspend it close to the spinning magnets, so it hovers a few mm away. It must be secure, because you don't want any crashes here! I bent my aluminum into an L along its long side, so it would mount on a nearby motor-mount post.
Now drill 3 holes in the bracket:
1) A mounting hole to bolt the bracket to the motor-mount
2) A smaller hole on the other end where the coil lives. A wire-tie loops through this hole and cinches the coil to the bracket. (Note lack of glue, because we might have screwed-up the coil and it's no fun to un-glue things later!)
3) A hole in the middle so your cable can pass through the bracket.
Solder the wires from the coil onto the end of your unbalanced cable. This cable will carry the signal from the coil through the inside of the projector to the jack, which will be added to the rear panel. You will need to strip the painted insulation off of the ends of the magnet wire. Use a match to burn it off, or some fine sandpaper to lightly scratch it away. Remember to insulate it with electrical tape or tiny heat-shrink tubing.
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