The inertial navigation thing was done with an ATMEL chip on the First robot and again with a PIC 16F877. By orientation of the 3 axis accelerometer you can make some assumptions. If you are accelerating straight down at 1 G the least of your problems is blinking the brake light. ;) Also the acceleration vector would change fairly quickly in a brake situation. You use more than just magnitude. You use the angle as well. not extremly difficult to solve nor over expensive. A lot easier than determining the position using integration of the acceleration as we did on the robot. Larry > > From: olin_piclist@embedinc.com (Olin Lathrop) > Date: 2005/09/02 Fri AM 11:42:28 EDT > To: "Microcontroller discussion list - Public." > Subject: Re: RE: [EE]: Looking formethodtodifferentiategravityfromacceleration > > Chris Emerson wrote: > >>> I thought that at first, but you can have other forces and still > >>> have a > >>> 1g vector. As an extreme example, add a 2g vector in the opposite > >>> direction. > >> > >> That example isn't included in my solution space. > >> I said above or below 1g :-). > > > > True, when it's != 1g you know there's some acceleration, but when it's > > 1g there might still be some. > > This is because you are treating a vector as a scalar. The 3 axis system > works in theory if you can subtract the gravity accelleration vector. > Unfortunately while its magnitude is easy (1g), it's direction is not so > easy to know without essentially doing an inertial navigation solution. > > While this is an interesting theoretical discussion, I don't think something > like this is practical for a car to determine braking. I've also got > serious concerns about the desirability of blinking a brake light in the > first place. > > > ***************************************************************** > Embed Inc, embedded system specialists in Littleton Massachusetts > (978) 742-9014, http://www.embedinc.com > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist