A serial to parallel interface (SPI) has been designed for a personal computer (PC) controlled solar spectroradiometer. The SPI allows for serial RS-232 communication between the radiometer and the PC. The serial data from the PC is converted to discrete, parallel control lines that connect to the various subunits of the radiometer. Data from these subunits are received in parallel at the SPI and converted to serial for transmission to the PC. Pascal programming is used to control all of the radiometer functions including tracking, filterwheel rotation and data gathering.