Page 229 - The Unofficial Guide to Lego Mindstorms Robots

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have a head that is 3/16" in diameter. You can use pan head or round head machine screws, but the pan head is shaped more
u
like a LEGO st d. Instead of drilling out the stud, just shave off the top of it, so that it's level with the surface of the brick.
Then you can drill a hole and thread the screw down into the brick. An example of this technique is shown at
http://www.kabai.com/lego/lego.htm . Again, you should replace diagonally opposite studs so that the sensor will be connected
to the RCX, regardless of the orientation of the wire brick.

You'll see an example of this technique later. In the meantime, here are some construction tips:

1. Begin by shaving off two diagonally opposite studs on the brick. A hobby tool like a Dremel™ rotary tool or Black and
Decker Wizard™ works well for this purpose if you have cutting disks for it.

2. Now make sure the screw heads are the right size. Some 4/40 machine screws have heads that are larger than a LEGO stud.
You can adjust the diameter of the screw by mounting it in a drill (with the head facing out). Turn on the drill and use a file to
reduce the diameter of the head. With round head machine screws, you may also need to flatten the top of the head. You can
test your modifications by trying to place the head of the screw in the bottom of a wire brick. You should only have to push it a
little bit to get it to fit.

3. Solder a short wire to the tip of each screw before you put the screws in the brick. There are two very good reasons for this.
It takes a lot of heat to solder on to the screws, so you don't want to either melt the plastic around the screws by soldering them
in-place, or burn out the sensor you're mounting by soldering it directly to the screws.

4. Thread the wires you just soldered to the screws into the holes in the top of the brick. Now turn the screws into the brick—
they should thread nicely into the holes.

5. Now you're ready to mount your sensor in the brick and solder its leads to the screw wire from Step 3. Make sure to use heat
sinks so you don't undo your previous work or damage the sensor.

Conductor Plate

Another technique for attaching sensors to the RCX's inputs is based on special conductive plates. These plates are available as
an accessory pack, #5037, from the LEGO Shop-at-Home service (800-453-4652). The kit, which is $6.75US, comes with
several plates to which you can attach your sensor electronics. This technique is fully described at:
http://www.akasa.bc.ca/tfm/lego_temp.html .