HMC6343 compass code for Axon, I2C

[Admin]

I got a HMC6343 Compass hooked up to my Axon, using I2C. Here is some code I'd like to share . . . don't forget to include the I2C AVRlib library.

Code:

//Read HMC6343 compass I2C data:
u08 TARGET_ADDR = 0x32;  //0x32 = HMC6343 compass slave write address
u08 command = 0x50;  //0x50 = post heading data, pitch data, and roll data
u08 in[6];  //6 bytes = MSB heading, LSB heading, MSB pitch, LSB pitch, MSB roll, LSB roll
i2cMasterSend(TARGET_ADDR, 1, &command);  //send 1 byte command to slave from master
delay_ms(10);
i2cMasterReceive(TARGET_ADDR, 6, &in[0]);  //read 6 byte data from slave to master

//process heading data:
compass = in[0];  //first byte is MSB heading
compass = compass << 8;  //shift MSB byte to top of int
compass = compass + in[1];  //add LSB byte (2nd byte) to bottom of int
compass = compass; // / 10;

//process pitch data:
pitchCompass = in[2];  //3rd byte is MSB pitch
pitchCompass = pitchCompass << 8;
pitchCompass = pitchCompass + in[3];  //4th byte is LSB pitch
pitchCompass = pitchCompass / 10;
if(pitchCompass > 6400)
pitchCompass = (pitchCompass - 6400 - 155);  //convert to negative values

//process roll data:
rollCompass = in[4];  //5th byte is MSB roll
rollCompass = rollCompass << 8;
rollCompass = rollCompass + in[5];  //6th byte is LSB roll
rollCompass = rollCompass / 10;
if(rollCompass > 6400)
rollCompass = (rollCompass - 6400 - 155);  //convert to negative values

Output of course is pitchCompass and rollCompass.

Also a comment on this compass . . . I'm using it on my robot fish. The fish uses a waterproof magnet switch . . . the magnet is weak, and 2-3 inches away from the compass, but still affects results by about +/- 13% (absolute value 27%). Hopefully that info helps someone!


edit: changed the % error, due to my own error

[Razor Concepts]

Are the heading readings you are getting good? I've tried using a HMC6352 (no tilt compensation) and the readings are not proportional, but in between 360 and 0 degrees.

[Admin]

Are the heading readings you are getting good? I've tried using a HMC6352 (no tilt compensation) and the readings are not proportional, but in between 360 and 0 degrees.

Hmmmm I haven't done any real testing of it yet to comment. But outside interference can definitely make it non-proportional!

[Ro-Bot-X]

I have an old Lego compass and I have noticed that it needs a bit of time to settle if the robot was moving and the measurements are not reliable while in motion, even it it is a streight line. This sensor is similar with the Devantech CMPS03, I had the same problems with that one too. So, it may be a good idea to keep the robot still while checking the compass, then let it move. Why? because of magnetic interference from the motors.

[Admin]

Why? because of magnetic interference from the motors.

Not to mention the power fluctuations in your system, and the 'moving' environment. What if your floor had a steel I-beam under it and you didn't know? etc.


note: I changed the reported error above, had a typo . . .