Far-seeker:
Have you considered using one or two accelerometers in place of some of the vibration sensors? This would give the ability to compare the readings from the different sensors and eliminate many potential false positives. In the USA making false calls to 911 can be a prosecutable offense, and I doubt you'll be very popular with the local police if they get a call because you accidently hit your helmet against something while holding it.
Hi Far-seeker,
First off thanks for the reply and I am sorry for my late response. Cos I thought I would be getting email notifications about replies, but it turns out to be not.
Speaking of the false positives, I was thinking about to set a certain amount of vibration pulse as default, so in order to make the calling function work, the amount of stress should simply be more than what I set in my program.
This is just an idea of mine, however I have no knowledge about electrical engineering nor programming. What do you think about feasibility?
Additionally, I also had an idea of making the calling or detection function start when the rider actually starts riding his bike. In this case I could use GPS system to detect the speed. Cos almost all smartphones have GPS sensors and plus the helmet is going to be connected to it. If there is a certain amount speed then the vibration sensor(s) will turn on. (may be your idea about the accelerometers is the same with what I just explained. If not, then please provide more detailed explanation)
Moreover, since this is the prototype and it is not required to make calls to 911, just for demonstration purpose I would use my own cell phone number.