RPI and 10 DOF IMU

[xyzones]

Hello,

i have a B+ with arch linux and installed all required i2c tools. I am using Adafruit_I2C python library and wrote my own LSM303. I just wonder if is that good to have magneto sensors X Y Z between a range of 0-65K but no negative numbers at all.

Code: Select all

		raw_mag = self.mag.readList(self.LSM303_REGISTER_MAG_OUT_X_H_M, 6)
		magnetometerVector = self.obj3d(x=0,y=0,z=0)
		magnetometerVector.x = ((raw_mag[0] << 8) + raw_mag[1])
		magnetometerVector.z = ((raw_mag[2] << 8) + raw_mag[3])
		magnetometerVector.y = ((raw_mag[4] << 8) + raw_mag[5])

Another question, where i am or I will use the rpi with the sensor there is a declination between +3° 59' EAST and +4° 14' EAST. When calculating the tilt compensated heading where do I add these, how to get the best precision for the heading?

I am building a sailboat computer, why precision is important.

Thanks,

Attila

[adafruit_support_mike]

The values returned from the magnetic sensor are 16-bit signed integers in twos-complement notation. Only the lowest 15 bits contain magnitude information. The highest bit indicates the sign.

To convert twos-complement to a signed integer value, you need something like this:

Code: Select all

if ( value & 0x8000 ):
	value = ( value & 0x7fff ) - 0x8000

[xyzones]

Hello Mike,

That seems to be better now thanks.

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		xla = self.accel.readS8(self.LSM303_REGISTER_ACCEL_OUT_X_L_A)
		xha = self.accel.readS8(self.LSM303_REGISTER_ACCEL_OUT_X_H_A)
		yla = self.accel.readS8(self.LSM303_REGISTER_ACCEL_OUT_Y_L_A)
		yha = self.accel.readS8(self.LSM303_REGISTER_ACCEL_OUT_Y_H_A)
		zla = self.accel.readS8(self.LSM303_REGISTER_ACCEL_OUT_Z_L_A)
		zha = self.accel.readS8(self.LSM303_REGISTER_ACCEL_OUT_Z_H_A)

		a.x = xha << 8 | xla
		a.y = yha << 8 | yla
		a.z = zha << 8 | zla

when the IMU is on my desk no movement at all i have the below 0.5 seconds responses for the above code

Code: Select all

-16 -48 -15792
-16 -16 -80
-256 -32 -80
-208 -48 -96
-240 -224 -48
-256 -240 -96
-208 -240 -128
-64 -96 -15808
-192 -240 -15792
-224 -32 -15760
-224 -32 -80
-224 -16 -15776
-240 -32 -15776
-240 -32 -80
-240 -48 -96
-208 -16 -80
-32 -32 -96
-240 -224 -15600
-240 -240 -64
-32 -240 -64
-192 -256 -48
-192 -32 -64
-16 -240 -96
-208 -32 -32
-240 -32 -80
-240 -256 -112
-224 -240 -112
-240 -240 -96
-240 -224 -80
-32 -64 -96
-32 -16 -48
-240 -224 -80
-256 -192 -16
-48 -240 -64
-224 -16 -112
-32 -64 -96
-208 -208 -16
-256 -240 -64
-32 -32 -128
-240 -16 -112
-224 -32 -15616
-16 -96 -96
-240 -256 -48
-16 -224 -64
-240 -48 -64
-16 -16 -112
-256 -80 -48
-16 -256 -48
-16 -224 -48
-240 -32 -48
-160 -256 -96
-240 -16 -64
-256 -80 -128
-256 -224 -48
-256 -240 -80
-16 -256 -48
-224 -48 -15584
-256 -48 -16
-208 -96 -96
-208 -16 -48
-224 -48 -80
-48 -256 -80
-240 -224 -32
-32 -256 -64
-256 -48 -112
-16 -48 -96
-240 -256 -112
-32 -16 -64
-64 -48 -112
-32 -256 -80
-32 -240 -80
-256 -64 -80
-224 -32 -112
-32 -224 -64
-16 -256 -64
-208 -256 -32
-176 -32 -112
-32 -16 -80
-208 -256 -112
-208 -16 -96
-16 -64 -16
-256 -32 -32
-224 -32 -48
-256 -48 -15600
-256 -224 -64
-208 -256 -80
-16 -240 -128
-16 -240 -128
-240 -48 -80
-16 -64 -128
-16 -16 -32
-224 -48 -112
-48 -256 -32
-48 -240 -64
-32 -256 -15584
-16 -48 -80
-208 -224 -48
-16 -256 -112
-32 -16 -48
-16 -256 -80
-224 -240 -128
-80 -240 -112
-64 -16 -128
-48 -64 -96
-224 -64 -128
-240 -256 -16
-48 -16 -80
-256 -208 -112
-16 -16 -32
-16 -96 -32
-256 -256 -16
-256 -32 -128
-16 -64 -15552
-16 -240 -15616
-208 -32 -96
-240 -16 -80
-224 -64 -15808
-240 -32 -112
-240 -32 -96
-256 -48 -64
-208 -48 -80
-240 -256 -48
-16 -48 -128
-32 -48 -15760
-32 -80 -48
-224 -64 -15776
-224 -256 -15616
-208 -224 -96
-240 -176 -16
-224 -224 -64
-192 -32 -80
-16 -48 -15600
-256 -256 -128
-32 -256 -80
-240 -16 -80
-224 -16 -96
-240 -240 -32
-240 -64 -80
-224 -224 -128
-256 -224 -48
-112 -16 -112
-16 -48 -128
-240 -64 -32
-208 -16 -15760
-32 -224 -48
-240 -48 -128
-16 -32 -128
-240 -16 -96
-256 -256 -80
-208 -256 -112

BANNED results are showing almost 0 movement.

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21 80 80
21 80 80
22 80 79
22 79 79
22 79 78
22 79 80
22 80 79
22 80 79
23 80 80
22 79 79
22 80 78
21 79 79
22 79 79
22 80 78
22 80 79
22 79 79
22 79 79
21 80 80
22 79 79
22 79 80
22 81 80
23 79 79
22 80 80

what am i doing wrong?

LSM303_REGISTER_ACCEL_CTRL_REG1_A is set to 0x47
LSM303_REGISTER_ACCEL_CTRL_REG4_A is set to 0x08

[adafruit_support_mike]

I'm not sure what's happenining there.. post the complete code you're using and we'll see if that gives us any clues.