122-28029 Parallax Inc, 122-28029 Datasheet - Page 131

• Manufacturer Part Number: 122-28029
• Description: GUIDE STUDENT SMART SENSORS
• Manufacturer: Parallax Inc

Specifications of 122-28029

• Accessory Type: Manual
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: Smart Sensors
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Chapter 4: The Hitachi HM55B Compass Module
The Hitachi HM55B Compass module measures direction. You can use it along with
your BASIC Stamp, Board of Education, and Parallax Serial LCD to make a digital
compass that works as shown in Figure 4-1. The module's Hitachi HM55B chip is an
increasingly common feature in automobile electronics, providing a compass heading for
the driver. The compass module is also a great tool for mobile robots, giving them a
sense of direction which can make a tremendous difference in robot team sports as well
as mazes.
This chapter uses modified versions of the programs from the Hitachi HM55B Compass
Module product documentation for testing and calibration. It also introduces averaging
as a way to filter measurement noise and demonstrates how to modify the existing
example programs to display the compass heading on the Parallax Serial LCD.
INTERPRETING THE COMPASS MEASUREMENTS
The Hitachi HM55B Compass Module product documentation has example programs
that all use a subroutine named
strength measurements. The value of x is the component of the earth's magnetic field
acting on the sensor’s x
earth's magnetic field acting on the y
aligned with the earth's magnetic field, then the x measurement at some angle θ will be N
cos θ, and the y measurement will be −N sin θ. Using these facts and a couple of
m
axis shown in Figure 4-2. The value of y is the negative of the
Compass_Get_Axes
m
axis. If N is the value reported by x or y when it is
Chapter 4: Hitachi HM55B Compass Module · Page 119
that returns x and y magnetic field
Figure 4-1
Hitachi Compass Module on the
Board of Education with an LCD
Display