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86 Masterpiece 2 • The Learning Brick Sorter

Bricks & Chips…
Multiple Connectors? Single Port?

How can the RCX distinguish between the readings coming from two sensors
attached to the same port? This particular trick works because the light sensor
returns readings that never reach the maximum value of its range. In fact, the
light sensor returns a number representing a percentage which in normal condi-
tions never read 100 percent. The touch sensor, configured as a light sensor,
returns either 0 when released or 100 when pressed. Thus, in the program we
can deduce that if the reading is 100 the touch sensor is pressed, otherwise the
sensor is released and the reading is what returned by the light sensor. This trick
is very useful to save input ports, provided that you don’t need to read the light
sensor when the touch sensor is pressed.

Final Step 26

Connect the motor attached to the
Body sub-assembly to Output Port A.