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I am trying to reach InvenSense MPU9150 magnetometer using master mode disabled and bypass mode enabled. These values are written to and then confirmed from the MPU9150 :

0x6B = 0x01, // Clock from gyro X
0x6A = 0x00, // I2C Master mode disabled
0x37 = 0x02. // Bypass mode enabled

I have then tried to reach the magnetometer through 0x0C->0x0F slave addresses but never received a correct answer from the 0x00 WHOAMI register. Have I missed a register ? The AUX pins on the PCB are floating. I can talk to the MPU9150 correctly and read the accelerometer and gyro data. Could the magnetometer in the MPU9150 be dead on arrival ?

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  • \$\begingroup\$ You might look at some of the published open source quadcopter control boards & firmware sources and see if there's an example of someone successfully using that function. \$\endgroup\$ – Chris Stratton Jan 8 '14 at 20:25
  • \$\begingroup\$ I confirm that the Magnet ID is 0x48. However I use master-slave mode. The address of the magnet is 0x0C. I tried to work with Bypass mode but no luck... \$\endgroup\$ – MooMoo Apr 24 '14 at 17:30
  • \$\begingroup\$ You need to wake up the magnetometer before you read, unfortunetly every time you read \$\endgroup\$ – Timtianyang Feb 16 '15 at 5:41
  • \$\begingroup\$ I am able to read the address of magnetometer 0x00 register but I am getting same data of magnetometer and 0x02 register always read zero . Its for whether data is read from register or not \$\endgroup\$ – user81282 Jul 17 '15 at 12:26
  • \$\begingroup\$ Have you verified that the MPU9150 is correctly hooked up to GND and VCC? One possibility is that your AK8975 is not powered, check page 28 of PS-MPU-9150A-00. \$\endgroup\$ – user96454 Jan 8 '16 at 0:28
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Do you get any non-zero answers when reading 0x00? I think that the datasheet is incorrect and WIA does not actually return 0x48, but I don't have a chip handy right now to test.

I'm not sure if there's any other registers that need to be set for the MPU to work, but for the record, I have it working and these are the MPU register values I use:

0x6B = 0x01; // Clock source is PLLGYROZ
0x19 = 0x04; // Set SMPLRT_DIV to 0x04; this gives a 200 Hz sample rate when using the DLPF
0x1A = 0x03; // 42 Hz LPF
0x6A = 0x01; // Disable master mode and clear all signal paths
0x1B = 0x18; // Full gyro range
0x1C = 0x08; // 4G accel range
0x37 = 0x32; // Interrupts pin stays high until cleared, cleared on any read, I2C bypass
0x38 = 0x01; // Data ready interrupt enabled

You could try putting it in FUSEROM mode (write 0x0F to register 0xA) and then reading the sensitivity adjustment values from registers 0x10 to 0x12; you should get the same value across multiple reads.

I'm not sure if there's a "proper" initialization sequence for the AK8975, but I've had the most success with: Put in FUSEROM mode -> read ASAX/Y/Z -> single sample mode, and then waiting on the DRDY interrupt (which, despite what the MPU9150 data sheet claims, is available on pin 14). I definitely had a large amount of trouble actually getting it to work correctly though.

One last question: what speed are you running the I2C bus at? The STM32F4xx line, at least, has issues running at 100 kHz--I have to run at 400 kHz to get correct functionality.

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From what I remember, once in bypass mode you're directly talking to the magnetometer. I suggest you try using an oscilloscope or logic analyzer to see whether your signals reach the magnetometer from your microcontroller.

If they do and you're getting a NACK, then get the right slave address for the magnetometer to make sure it's being addressed. Be careful with 7 and 8 bit representations of the address.

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