A co-ordination control system for a camera and a motor drive unit with separate electrical power sources one of which has a higher voltage than the other. The system is provided with an interface circuit including two switching elements arranged to cooperate with a common release button and connected between the circuitries of the camera and the unit so that the higher voltage of the source in the unit is prevented from being applied to the circuitry of the camera. For remotely controlled photographic purposes, the system is further provided with a control circuit for actuating these two switching elements in time-displaced relation to each other.