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PneumADDic II • Masterpiece 4 183

an electronic circuit by converting it to heat. PneumADDic II uses touch sensors and
resistors in two different types of circuits:

■ The series resistor circuit
■ The parallel resistor circuit

Both of these circuits will be explained in more detail later in the chapter.
When I realized that I needed resistors to combine multiple touch sensors onto a
single RCX sensor port, I was unsure of how much resistance was necessary, so I decided
to use variable resistors called potentiometers.
You can adjust the amount of resistance in a potentiometer by turning a screw that
protrudes from the device.The next challenge was to figure out how I could easily incor-
porate these potentiometers into LEGO models. I decided to create my own poten-
tiometer bricks that could be snapped into place in a LEGO assembly, similar to the
bricks that LEGO makes. When you create your own RCX sensors, they are traditionally
called home-brew sensors. I call the resistor blocks I made home-brew potentiometer bricks.

NOTE
You will probably have to order your potentiometers from an electronics part
supplier, as they are not a LEGO product. I got my potentiometers from Digi-Key
Corporation (www.digikey.com), product number CT20P103-ND. These poten-
tiometers are adjusted by turning a screw on the end of the case. It takes 10
complete turns of the adjustment screw to increase the potentiometer’s min-
imum resistance of 0 Ohms, to its maximum resistance of 10,000 Ohms (or 10K
Ohms).

The Potentiometer Brick

The next section of building instructions shows you how to create a home-brew poten-
tiometer brick.The Potentiometer Brick sub-assembly requires the modification of some
LEGO parts, soldering equipment and solder, and a strong adhesive. Some LEGO purists
would find this appalling, but the potentiometer bricks work very well.You will need
some special plates from LEGO, specifically electric plates. Electric plates look similar to
normal plates, but contain metal to allow you to electrically connect cables together.
We need to cut away parts of the plates to allow access for electrical wiring.The
Potentiometer Brick sub-assembly also requires soldering (similar to the effect hot glue,
but for electrical connections), and some glue to fortify the sensors when they are done.