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182 Masterpiece 4 • PneumADDic II
OR Gate Tube Guides Step 2

The Issue of Sensors

PneumADDic II uses a total of ten touch sensors, but only one RCX.The RCX has
three sensor inputs.The question is, how do we get 10 touch sensors to connect to the
RCX so that it can tell which touch sensors are being pressed? We do this by some elec-
tronic slight of hand.
The RCX contains a battery-operated digital computer.As we learned earlier, digital
computing is limited to ones and zeroes.The sensors available for the RCX are analog,
meaning that they can provide a wide range of readings. How is it possible for the sensors
to communicate with the RCX, when the RCX is digital and the sensors are analog?
The RCX contains a device called an analog to digital converter.The analog to digital con-
verter computes a 10-bit binary number for any given analog value provided by a sensor.
Touch sensors are binary devices in that they only provide two values:

■ Touched
■ Not touched

The RCX reads values from the touch sensors using the analog to digital converter. It
is possible to combine two or more touch sensors onto one RCX input port by assigning
each touch sensor a different analog reading value to be interpreted by the RCX.This is
accomplished by adding electricity resistors in between the touch sensors and the RCX
analog input. Electricity resistors, or simply resistors, dispose of some of the electricity in