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Preston_5564C04.fm Page 123 Wednesday, October 5, 2005 7:22 AM

CHAPTER 4 ■ SENSORS 123

Section Summary

This section showed three different orientation sensors (compasses) and the software to get
those readings to your PC. The three compasses discussed were the Devantech CMPS03 digital
compass, the PNI Corporation Vector 2X, and the Dinsmore 1490.
I created two Java classes and one BASIC Stamp program as described in the following
bullets:
• Compass.bs2: A BASIC Stamp program to get sensor readings from one of the three
compasses
• CompassStamp.java: A Java class that models the BASIC Stamp configuration connected to
the three compasses
• Compass.java: A single compass class that’s used to connect to the Devantech CMPS03
compass
I would recommend the Devantech compass because of its response time, accuracy, and
single I/O pin.
The next type of sensors will return logic data—either a true or a false.

4.2 Switch Sensors

The types of sensors I’ll talk about in this section return a logic high (3V to 5V) or low (< 1V) to
your microcontroller. The four examples I’ll use will be

• Bump Sensors: Great for letting you or your robot know if it’s hit something.
• Line Detectors: Excellent for following lines, or for us as encoders or boundary edge
detectors.
• Proximity Sensors: Great for letting you or your robot know if it’s close to something.
• Combination Switch Sensors: When you have more than one logical sensor you want to
return data from at the same time.
The first sensor pictured is the bump sensor, shown in Figure 4-11, in which we see the
Lynxmotion Bumper switch assembly kit. These are nice backups to proximity sensors because
sometimes nonmechanical sensors can return false readings or the delay time is too large for
the speed of your robot. For example, if your robot is traveling at 36 inches per second and you
read the sensor five times a second, the sensor resolution is 36/5 or about 7 inches. Double that
speed and it’s 14 inches.