How do Garmin sensors work?

I finally gave in. Polar have served me well over the years - in fact - they have been pretty much fantastic. With the use of Strava - I found myself gathering speed / altitude / time / heart rate on my Polar (cx600x) - and logging the ride for Strava (as we all know - if its not on Strava - it simply did not happen) by phone.

Me being me I found myself all too often off the back of the fast group, and off the front of the intermediates - as such - one wrong turn and I am lost. Enter Garmin, enter uploading the route for the day, enter compliance with the hardware choice de-jour.

The polar had a more traditional wireless setup. Sensors, magnet, leaf switch, transmitter, job done.

The new Garmin Ant+ sensors do not have a magnet. They just sit on the crank arm, and on the hub. They go around - and that is about that - they do not interact with anything.

In my head I am thinking of proximity, metal, hall effect, maybe they are not even that accurate and work on repetitions of light dark, magnetic field changes... all of which seem to unsuited to the task. It left my mind - and all was well in the world again.

This weekend someone asked what the lump was, and how it worked (a fellow engineer) - and the answer was I REALLY DON'T KNOW AND NOW YOU HAVE REMINDED ME!

So - how do the new Garmin sensors work... fret no more: Magnetism.

More specifically magnetic fields. As it rotates, the polarity of the earth will appear to flip. One flip = One rotation. Whether that be in the horizontal or vertical plane - you are going to be able to tell when something has passed through 180 degrees.

My concern with that as a solution was the speed at which it would need to sense that (having got a compass on my watch / phone - they don’t exactly seem sporty - but then again compass' are oil filled to dampen them - so maybe this was to recreate the UX?)... but apparently not. This is how these are done.


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