Wondering what could be the simplest way to implement a basic sensor to measure my cars' speed wrt ground, every 5 sec or so for a period of 1 or 2 hours time? Not precise but consistent.
Additional log implemented in a RAM with automatic time stamping plus eventual "bookmarks" at the push of a button.
No display but reading when at home just to evaluate my driving performance
Power supply, a 9V battery (by no means associated to the car's common). Tapping into the car's wiring (whatever it is) is not considered.
Comments and caveats appreciated.