Hello all
We rquire a sensor circuitwhich will be mounted about 5 meters away from the gate entrance. When the car approaches, it must detect the speed. This speed must be able to be set on the sensor with a simple pot and lcd screen. (Turn the pot up-down to increase/decrease the speed). When the sensor detects any set speed, it must trigger off a relay. That is all. Is there any such circuit available

 

There should be of the shelf devices in the market but in case you can't find one you can build one with ultrasounds.