130-28029 Parallax Inc, 130-28029 Datasheet - Page 136

• Manufacturer Part Number: 130-28029
• Description: KIT PARTS SMART SENSORS
• Manufacturer: Parallax Inc

Specifications of 130-28029

• Accessory Type: Education Kit
• Product: Microcontroller Accessories
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• For Use With/related Products: BASIC Stamp®
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Contains lead / RoHS non-compliant

Page 124 · Smart Sensors and Applications
Your Turn - Experiments with Magnetic Fields
There aren't all that many places where the earth's magnetic field is parallel to the ground.
It's either pointing into or up from the ground. The angle at which the Earth's magnetic
field points into or out of the ground is called inclination.
Declination is the measure of degrees between magnetic north and true north. For the
United States, you can find information on the difference at http://nationalatlas.gov. At
the time of this writing, an article with information about both inclination and a map of
declinations was at this page:
One of the maps on this page also shows the total magnetic field intensity in nanotesla
measurements. The tesla (T) is a measurement of magnetic field intensity, and nanoteslas
(nT) are billionths of teslas. The readings the compass module's x and y axes return are
in approximately millionths of teslas (µT). According to the HM55B's chip datasheet,
your compass module’s units could be anywhere from 1 to 1.6 µT.
http://nationalatlas.gov/articles/geology/a_geomag.html
LOOP UNTIL status = Ready
SHIFTIN
HIGH En
IF (y.BIT10 = 1) THEN y = y | NegMask
IF (x.BIT10 = 1) THEN x = x | NegMask
RETURN
√
√
√
SHIFTIN
Hold your board level, and align your compass module's x-axis with magnetic
north. When the x-axis is aligned with north, the Debug Terminal should display
the largest x value, and the angle should read 0 degrees.
Keep pointing your compass north, but try tilting it up and down. Chances are
you'll find an even larger measurement at a certain tilt than you do while holding
it level. That's because the magnetic field is either pointing into, or up from, the
ground in your locale.
Make a note of the very largest x-axis measurement you were able to achieve.
DinDout,clk,MSBPOST,[x\11,y\11]
DinDout,clk,MSBPOST,[Status\4]
' Get Status
' Exit loop when status is ready
' Get x & y axis values
' Disable module
' Store 11-bits as signed word
' Repeat for other axis