I think you can use peizo sensors mainly cables or sheets, piezo power harvesting ICs are there (ex:from leniar technologies), use some lower end micro controller works in very nA range with internal eeprom. using the energy generated when vehicle moves over the piezo electric material you can make the controller work and write it to eeprom using the energy generated from piezoelectric material. i have done some work on this like harvesting power when u walk. so i think it would be easier to get enough energy (2mJ) from a vehicle movement. YOurs SaRIn.... On Sun, May 16, 2010 at 11:27 AM, Russell McMahon wrote: > > When I mentioned low mass, I was referring strictly to a compass like > > device, that would indicate a slightly different direction as the > > large steel vehicle interacted with the Earth's magnetic field. > > Consider "reluctor" as per electrons motorcycle ignition. > > U laminations with coil and magnet in series. U facing towards > vehicle. As V passes magnetic fieldi s somewhat closed. How well and > how close needed TBD. > > > R > -- > 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