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Urgent - Need 3.3V tolerant Compass

screamingtiger

Cliffs:  Anyone know of a magnetic compass that works with the raspberry Pi, I2C and is 3.3V tolerant on the SDA/SCL?  It may need to be tilt compensated.  Please have first hand experience using it, I need it to work I cannot afford any more trial and error.  Thanks!

 

Details:

I've had some serious issues with my quadcop_project in terms of getting heading.  I've tried a mems sensor from xtrinsic but its not compatible via I2C with the Raspberry Pi 2.  It works fine with RPi B+. I digress.

 

I have an HCM5883L breakout and realized its not 5V tolerant, I think I burned it up and the data doesn't make any sense to me.  It is suppose to return a value between 0 and 255 but the registers are 16 bit with MSB and LSB being read independently.

https://www.sparkfun.com/products/10530

 

The examples from the Arduino don't make any sense.  Its really simple to use:

https://www.sparkfun.com/tutorials/301

 

You can see the values they are getting there.  A couple of odd things, the datasheet says it returns the data in 2 compliment form, which to me says I need to flip the bits but the sample code does not such thing. 

 

Regardless, I am not sure how to use this because it has 3 axis!  There is very little information on this board and no idea why I would want a 3 axis reading and how I would use that to calculate north.

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    BTW, After tinkiering some more I got it working with the raspberry pi directly using the wiringPi library.    I am so glad I ordered two of these because one of them is way off and sends random data.

     

    The sensor allows you to "write" to one of the registers and what it does is sets a pointer to that register, so when you start reading data it updates the pointer and the next read will be fore the next register (to get X,Y and Z information).  For some reason, this works good with arduino.

     

    However with the raspberry pi I must manually update the pointer, first sending a write byte to each register I want to read in order.  Its just a normal read now, where I specify the register I want to read.  But that was throwing me off.

     

    I now incorporated this into my multithreaded GPS object so it will update every 2 seconds.  The code you sent me was a life saver as it allows me to calculate a heading.  the heading is not accurate at all, but it is consistent and for my project that's all I need.

     

    One thing ODD, the ardunio examples just show the arduino connecting directly to the sensor, though the sensor needs a 3.3v source..   Its not clear if level shifting is needed.  On my breakout board there is also a single regulator making me wonder if it can take in 5V on VCC.

     

    No time to research this.

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  • 0

    BTW, After tinkiering some more I got it working with the raspberry pi directly using the wiringPi library.    I am so glad I ordered two of these because one of them is way off and sends random data.

     

    The sensor allows you to "write" to one of the registers and what it does is sets a pointer to that register, so when you start reading data it updates the pointer and the next read will be fore the next register (to get X,Y and Z information).  For some reason, this works good with arduino.

     

    However with the raspberry pi I must manually update the pointer, first sending a write byte to each register I want to read in order.  Its just a normal read now, where I specify the register I want to read.  But that was throwing me off.

     

    I now incorporated this into my multithreaded GPS object so it will update every 2 seconds.  The code you sent me was a life saver as it allows me to calculate a heading.  the heading is not accurate at all, but it is consistent and for my project that's all I need.

     

    One thing ODD, the ardunio examples just show the arduino connecting directly to the sensor, though the sensor needs a 3.3v source..   Its not clear if level shifting is needed.  On my breakout board there is also a single regulator making me wonder if it can take in 5V on VCC.

     

    No time to research this.

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