US Patent 7855573 Controller area network active bus terminator

A terminator for a CAN bus includes an electronic relay and a termination impedance. The electronic relay has first and second control input conductors and switched output conductors. The electrical connection between the switched output conductors is normally closed. The first control input conductor is connected to the power conductor and the second control input conductor is connected to a fifth terminal of the first CAN bus connector. The termination impedance is connected in series at the end node of the CAN bus with the switched output conductors across the high data conductor and the low data conductor. By this arrangement, the termination impedance is effectively connected across the high data conductor and the low data conductor at the end node of the CAN bus until an extension of the CAN bus is plugged into the first CAN bus connector. When an extension of the CAN bus is plugged into the first CAN bus connector, the fifth terminal of the CAN bus connector is connected to the ground conductor. This actuates the relay and opens the switched output conductors.