The Magnetometer

Posted on February 01, 2014 by Gary Carruthers

Clink Street, London, 1st February 2014

For reasons you'll discover later this year, we've added a magnetometer / accelerometer chip to the Shakespeare movement that powers the No.8, No.9 and No.11.

I2C interfacing to a new chip is always a pain, but finally, Hoorah!, we can talk to it!  ("Happy Days," as Magic Mike says.)

Then the basic physics begins.  What gauss readings should we expect?  What, you mean the magnetic dip here in London is twice the horizontal component?  Never knew that.  So we'll have to make sure the user holds the watch horizontal.  How are the sensors made?  How do we normalize their values? (The field strength varies across the globe.)  What are the soft-iron and hard-iron effects?  Will we have to put each watch on a turntable for calibration?  Will the magnetic field of the turntable motor affect the reading?  What about the magnetic field generated by the stepper motors on the watch, for that matter?  And the Bluetooth antenna?  Should we use the GPS in the phone to correct magnetic north to true north?  Is the permeability of steel cases too high?  Will this model have to be in gold and cobalt chrome editions?

And so the list goes on.  No day is the same as the last, but it's all good science.  Today, the physics of magnetism.  Yesterday, it was the chemistry of powder production for laser sintering in steel.  Tomorrow, who knows what. 

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