I would like to modify the third brake light of my car to add blinking when a strong deceleration is detected.
What threshold should I set? given the basic rules of friction, the maximum possible deceleration on flat roads is (friction coefficient) * g. That is about 0.9 g.
I thought about setting 0.6 g, since getting 0.5 g is quite easy to achieve and cannot be regarded as "strong" deceleration, worth a warning like blinking the third brake light.
The sensor will detect only acceleration in the driving direction, no side acceleration and no detection of gravity: depending on the pitch of the car, the effective deceleration needed to trigger the blinking may be slightly higher or lower.