Manual and computer control is a basic function built into all USB relay controllers we have manufactured for many years.  Manual control allows you to control a relay from the USB port or manually through an external input.  Relays are controlled manually when a analog input is first mapped to a particular relay.  Once mapped, the analog input has control of the selected relay.  When the analog input is high, a relay can be set to activate.  When the analog input is pulled low, the relay will deactivate.  This allows sensors and limit switches as well as the USB port to share control of your relays, based on user configuration.