hi..
i'm doing this as my project.. i dont understand the concept behind this.. please explain the working..first of all is this circuit correct..will it work?

 

It's not 'radar' it uses magnets on the drive shaft to measure the "speed" of the drive shaft and convert it into speed car travels.

Moderators may shut this thread down, auto topics aren't allowed. BUT if you are measuring speed of a electric motor, that's different

 

What du Google say. Try something like this-> martin pot digital speedo. Thoose who seek will find.