Switching circuit

I want to make a switching device with following features:

One senor will sense speed(frequency of a moving car, then this is fed to my circuit(to be designed). This circuit has three relays which are actuated when three pre-decided values of frequency(or current) are achievedi.e. there are three events-1. when certain frequecy(sensed by speed sensor) is achieved, first relay operates,2. on higher frequency second relay operates and 3.on further higher frequency third relay operates.
Please help me,
alok

Hi!

You should use a frequency to voltage IC and 3 comparator gate. Adjust the thresold of each gate so it put on the relay (by passing by a transitor and a diode) at the good level. Good luck,