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The increased capabilities of minicomputers today allows a biomechanics laboratory to establish a self-contained computer system for a reasonable price. The system includes a microprocessor, a printer and a CRT. Analog to digital conversion is an important feature to consider as well as the ability to interface with a mainframe computer. A minicomputer adapted for film analysis should be a consideration for data analysis when developing a cinematography laboratory. For the past 10-15 years the area of biomechanics has enjoyed the advances in technology. Equipment and instrumentation once used exclusively by engineers and physicists have become readily available to those involved with snorts analyses. Among the various pieces of equipment accessible to biomechanists today, probably the most important one is the computer. At this time several biomechanics laboratories are using the computer to analyze kinematic and kinetic data obtained from film. The computer in use at each school is generally the main University or College computer with a remote terminal set-up in the biomechanics laboratory. This system functions well if there is adequate response from the time-sharing system of the main computer, and if there is at least one knowledgeable technician available. With the trend toward minicomputers today, their increased capabilities, and their ease of use, a self-contained minicomputer system in the biomechanics laboratory appears to be a viable alternative. The computer system in use in the ,Biomechanics Laboratory at the University of Oklahoma is based around the Cromemco Z2D computer connected to a PCD motion analyzer (Figure 1). The data acquisition system consists of the eight-bit microprocessor-based minicomputer connected to an analog to digital converter (ADC). As a terminal for the computer, we have either a video display unit or a Model 43 Teletype. The Model 43 provides a hard copy out-put while the video terminal provides much faster I/O, useful for debugging and program development. The computer itself consists of the high current power supply mounted behind a 22 slot card cage. The CPU, 48K-byte memory, and I/O cards plug into the S100 card cage slots. The size of the power supply, in addition to the large number of card slots, give the Cromemco Z2D considerably more flexibility and expandability than more common "home computer" systems. The basic computer also includes two 51/4 inch flexible disk drives with a disk controller card capable of running four disk drives. As mentioned, one of the slots contains a card for analog to digital conversion. This particular card has seven analog input channels and seven analog output channels. Two of the analog inputs are allocated by the biomechanics program to the x and y data channels of the PCD film analyzer. In between the PCD machine and the ADC inputs, it is necessary to use a few circuits for analog signal conditioning. These circuits are used to match the 0 to 5 volt output of the film analyzer to the -2.56 to +2.54 voltage range of the ADC. In additon to the analog conversion card mentioned above, other cards available include parallel I/O, serial I/O, and TV video display drivers. The serial I/O card supports two channels of serial data which are useful for communication with other computers via a modem and output to printers. Figure 2 illustrates the configuration of this set-up. Although the cost of the Cromemco Z2D ($10,000) is somewhat higher than other computers available, the A-D conversion and extensive I/O canabilities are important features that must be considered. The system can either stand alone or be interfaced with a mainframe computer via a serial I/O port, another important asoect when time-sharing is not only expensive but difficult to obtain. A third reason for choosing this computer is its compactness; it is small enough to be placed on a moveable rack and can be rolled around to any location without the need for exoansion interfaces or additional power supplies.
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