Open Collector Outputs are used primarily for the purposes of controlling external DC relays and some very small DC solenoids. An open collector output is different than a relay output. Open collector outputs allow the user to control the connection of an external device by connecting and disconnecting the ground wire under software control. To drive an external 12V relay, +12V should be connected to one side of the relay at all times. The other side of your relay should be connected to our Open Collector output. Use our open collector outputs to make the connection to ground under software control. Open Collector outputs are also known as low side drivers (meaning it switches the ground line). In this way, different devices of different voltages may be controlled, providing all power supplies can share a common ground. A relay can provide you with a simulated open collector output by simply by connecting one of the relay outputs to your power supply ground. For wiring diagrams, please see the XR manual page 8.