A Sine-Wave Grating Controller for Vision Testing

This report summarizes design, development and testing of a microprocessor-based system that controls brightness and contrast levels of video monitors. This controller is to be used by scientists in maintaining calibration of video monitors during vision research. Prototype hardware for a video controller was designed and built. The controller requires a sine-wave grating to be displayed on a cathode ray tube (CRT). Luminance samples are measured directly from the CRT via a 512-element photodiode array. Analog information from the array is digitized and stored in a Z80 microcomputer. The sampled data are then used to compute CRT brightness and contrast. Computed brightness and contrast values are compared with desired values, and corrections are made to brightness and contrast control circuits for the video monitor. Most of the hardware required for the controller was built and tested. Hardware completed included the video sampling and digitizing circuits, as well as Z80 input/output and user interface circuits. In addition, all of the controller software was written and tested. Additional development is required before a working controller can be demonstrated. Brightness and contrast control circuits must be built and tested. Anomolies in performance of the commercially-procured video sampling circuits should be examined. Finally, closed-loop system operation must be tested and analyzed. (Author)