Wheel speed sensor

[Archangel]

Im looking for a way to measure automotive wheel speed on the wheel itself. I cant use a hall effect sensor and magnet behind wheel. It has to be a stand alone unit "self powered". Im thinking about an accelerameter or such device. Im using PBP and 16F877A

Your question is general "automotive" Is there a specific vehicle or do you want to fit all ? The reason for my question is, most late model vehicles were / are available with antilock brakes and as such have sensors already which can be accessed. Other options include optical reflective sensors, passive magnetic as Charles mentioned, speedometer cable / sensor options etc . . .

[rhino]

One idea for a self-contained unit could be built off the same principle as an mechanical engine governor. As the centrifical force increases, the resistance could change.