Design and construction of a microdensitometer computer interface

Abstract

This project consisted in modifying the output of a scanning microdensitometer so that a computer could accept and process the (optical) density versus position information gathered from radiographic film. The system functions were separated into two parts: the actual datagathering process, which required real-time response, and the calculation associated with the data. Separation of functions allowed a less expensive system overall while still preserving flexibility. For the real-time control computer, a relatively slow microprocessor-based system (Motorola MC6800) was chosen. The microdensitometer was modified to allow computer control of the scan. The density versus position information was digitized using optical shaft encoders. Cassette tape was used as a mass-storage medium for complete scans. Using an acoustic coupler, the microprocessor was cofigured to transmit accumulated data to a timeshare system for analysis. The results were retransmitted and displayed on a TV screen or printed on a line printer or teletype. The total cost of the microprocessor system was a little less than $5,000. The time required to produce the software was 50 to 100 hrs (approximately 1 week).