See subject.
It occurred to me I never knew how any pedometer works.
My guesses, each of which I think is too complicated by half:
Heart rate monitor:
Strain-guage for pressure sensation from vein; or
CMOS that notes the occlusion of the little LEDs on the vein side, occurring each time the normal-“cylinder” (cross section) of the vein splats out on each pulse.
Pedometer:
Accelerometer, adjusted for sudden spike to ignore more-continuous hand motions.
You’ve got the Pedometer correct I think. The heart rate monitor registers the change in skin “color” from your pulse, sending light from a couple of leds and registering the level of returned light. (Off the top of my head.)
Accelerator without gyros must be a strain-gauge also, right?
Yes, micro-machined 3-axis strain gauges.
Something that bothers me about the FitBit and all other devices of this type: Do they distinguish between walking and, say, riding in a car? And if so, how?
J.
I would suspect that they look at the acceleration signal. Walking would generate a repetitive up/down signal, while driving in a car would be much smoother (and probably more acceleration, too).
My Fitbit worked very well at not counting any false “steps” while driving/riding in a car (on normal paved roads) before I lost it.
My fitbit for the most part does a pretty good job with not counting car bumps as steps. There was one trip I did in Glacier National Park on the old red buses they have. I was sitting in the back and it seemed to me that fit bit was giving me steps because of the rough ride.
It does seem very good at distinguishing steps from activities that are moving but smooth. If I ride my road bike it barely registers anything, but off road on the mountain bike it will register some phantom steps.
When I hit certain rumbly sections of pavement on my bike, it puts my fitbit into sleep mode. Sort of annoying.
Also annoying is that a hard, sweaty bike ride into a headwind seems to count for less to my fitbit than a casual walk.
It can also get false negatives - I use a wristband version (versus a clip-on) and when I grocery shop, I’ve learned to put it in my pocket. Otherwise I spend 40 minutes in the store, and find I’ve walked a grand total of 300 steps (because of the hand being on the grocery cart handle).