How do digital speedometers work? — Eric, Burke Va.
Not so long ago, the speedometer and odometer in your car were mechanical devices. But most cars today have a digital dashboard. This means that computer is displaying information on the dash using either digital displays or electronic dials. The basic idea behind a digital speedometer is to somehow sense how fast the wheels are spinning, massage that data with a computer and then display it on the dash. There are many ways to get the information about wheel spin rates. There could be a magnet or optical sensor on the drive shaft, or something like an anti-lock braking sensor might provide the data. For more info see: How Dashboard Displays Work