In SX Microcontrollers, SX/B Compiler and SX-Key Tool, sprat wrote:

There's lots to learn.

First, even though the HM55B does give 11 bits, on the surface of the Earth you'll only get 6 bits of useful information.  (the Earth's field is 45-65 µT, and the unit measures in µT.)

Second, the Earth's magnetic field is not parallel to the ground, so when you measure the field, parts of it go into the ground.  If you only have a 2-axis compass you'll miss the third component, and if you bank on turns this can throw off your direction.
I do know of a 3-axis magnetometer from Honeywell that gets 1000 times the resolution of the HM55, but it costs $200, and it's not available from Parallax (sad day).

If you want true heading, instead of just magnetic heading, then you'll also either want a GPS unit that can give it to you live, or look up the value on a plot on wikipedia or something if you're only going to be using it in a localized area.

I'm currently working on a device that will use GPS, a 3-axis accelerometer and two HM55's to tell which direction it's facing.  (The accelerometer is so it knows which way is down, so it can ignore that component of the magnetic field.)

The web link on page 4 of the "Hitachi HM55B Compas Documentation" is great if this is your first technical experience with the Earth's magnetic field.

---------- End of Message ----------


You can view the post on-line at:
http://forums.parallax.com/forums/default.aspx?f=7&p=1&m=198637#m198987

Need assistance? Send an email to the Forum Administrator at forumadmin@parallax.com

The Parallax Forums are powered by dotNetBB Forums, copyright 2002-2007 (http://www.dotNetBB.com)