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HCM 5843 Magnetometer DIYdrones Board

I2C Interface

Behavior of the Data Signal

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I´m experiencing a strange behavior of the signal of the HCM magnetometer.

As you´ll see in the next pages, as soon as the board is power-up, the signal is very good and remains good for a period of time.

After 8 minutes approximately , the signal begin to deteriorate and became useless ...

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The Hardware

Arduino Duelmilanove

I2C InterfaceSDA=A4 (Yellow) SCL=A5 (Orange)

7809 Volt Regulator to Arduino Vin

Serial Comm with LabView

13.8V Batt to 7809 Regulator To keep

attached to a leveled surface,

and static

9V from 7809

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The Hardware

5V from Arduino

Yellow wire = SDAOrange wire = SCL

4k7 pull-up resistors for

SDA and SCL

GND from Arduino (black

wire)

5V from Arduino (red wire)

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Code for Arduino

I got measurements with two diferent codes for Arduino with the same results:

- A code from ArduIMU that uses the Wire library

- A code that uses the HMC library

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Results

- The Arduino board sends, through serial port, the data to the computer (approx. sampling rate 8.33Hz);

- On the computer there is a LabView program that deal with data and show it in the way that you´ll see in the next pages;

-The data that Arduino sends:

Mag X = raw data from magnetometer

Mag Y = raw data from magnetometer

Mag Z = raw data from magnetometer

Heading = calculated from the data above

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After 2 minutes:2 min0 min

Good data, no spread (see Histograms) and very low standart deviations (click to see)

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After 5 minutes:5 min3 min

Data remain good, no spread (see Histograms) and very low standart deviations

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After 8 minutes:8’ 20”6’ 20”

( * ) start of the problem, increase in the spread (see Histograms) and in the standart deviations

( * )

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After 10 minutes:10 min8 min

High spread (see Histograms) and high standart deviations, make the data useless

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After 14 minutes and 30 seconds14.5 min12.5 min

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After 25 minutes25 min23 min

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Questions

- What am I doing wrong?

- Why as soon as the board is powered-up the data is good and reliable?

- Arduino and the HCM5843 board are not compatible?

- Could my HCM5843 board be defective?