A simple, low-cost, multiplexed Hadamard-type spectrophotometer based on a spinning disk containing 63 separated masks has been constructed to obtain spectral data in time intervals down to 50 ms. Each mask contains 63 resolution elements. Optical localization and identification of the masks were implemented in the disk to avoid misalignment problems. The control of the spectrophotometer and data acquisition was made by using a dedicated single-board microcomputer based on an 8085 CPU. The single board microcomputer sends the data, through an RS-232C interface, to an IBM-AT compatible microcomputer where the Hadamard transform is performed to recover and display the emission, transmittance, or absorbance spectrum. The instrument has been used in the visible range to obtain absorbance data for time-resolved flow injection analysis applications.461218221827