I didn't have time to write an update last week, but I did make some progress.
I've gathered more data, of me working on my Standing Desk, myself walking, but also of a friend sitting.
I've cleaned up the data, and I've compared the 3 states. I created a graph of the accumulated force for each stated, which can be found here.
I created another graph, which is basically the same one, with a limit of 1000 records, and a timelined X axis (values were sampled every 50ms, so you'll need to multiply the X axis values with 0.05 to get Time).
For our purposes, it looks like the algorithm to distinguish between sitting/standing and walking is going to be quite easy. It looks like my walking has a very distinct pattern that repeats every 1/2 seconds (or 10 samples).
So I'm thinking of gathering min & max every second, and flagging it as "active" or "inactive". Then we can distinguish walking vs sitting/standing based on the amount of active seconds.
But, being in Istanbul for vacations, and since I didn't think far enough to bring my Arduino with me, I'll work out the algorithm on the sample data I have, and then onto the actual stuff.