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MIT 6 111 - Video Track and Shoot System

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Visual Object Tracking and Target System Checklist of Deliverables Jaime Lien Willie Sanchez At its completion, our system will be able to do the following: • Feed sync signals into a television camera and receive from it a composite video signal. • Process a composite video signal, using color comparison to locate the position of an object. • Determine a moving object’s velocity. • Use an object’s position and velocity to predict its future position. • Aim a projectile launcher at an object’s predicted future position such that, when fired, the projectile will hit the object. • Follow an object’s movement with a laser beam.Video Track and Shoot System Jaime Lien Willie Sanchez Introductory Digital Systems Laboratory TA: Jia Fu Cen May 12, 2004 Abstract This system is designed to track and shoot a person or object moving in two dimensions. An NTSC camera is positioned to capture an area in front of a black backdrop. A laser pointer and a toy gun are each mounted on two stepper motors to allow rotation along two axes. The laser follows the target’s motion; the gun aims at the target’s predicted future position to account for the projectile flight time of its using its current position and speed. The system is comprised of two digital subsystems: a video interface and a mechanical interface. In the former, analog video input from the camera is converted to digital and processed to determine the target’s position coordinates and speed. These coordinates and speed values are then fed into the mechanical interface, which uses them to perform a linear estimation of the target’s future position. The mechanical interface then drives the stepper motors to aim the laser pointer at the target’s current position and the gun at its future position.Introduction This system is designed to track and shoot a person or object moving in two dimensions. An NTSC camera is positioned to capture an area in front of a black backdrop. A laser pointer and a toy gun are each mounted on two stepper motors to allow rotation along two axes. The laser follows the target’s motion; the gun aims at the target’s predicted future position to account for the projectile flight time of its using its current position and speed. The system is comprised of two digital subsystems: a video interface and a mechanical interface. Both are run on a 10-MHz clock. In the former, analog video input from the camera is converted to digital and sampled at a resolution of 80 by 60. At each sample point, the digital luminance value is compared to a threshold luminance value. The coordinates of points corresponding to whiteness are averaged at the end of each frame to determine the center of the target. Center coordinates from two consecutive frames are then used to calculate the person or object’s speed. These coordinates and speed values are then fed into the mechanical interface, which uses them to perform a linear estimation of the target’s future position. The mechanical interface then drives the stepper motors to aim the laser pointer at the target’s current position and the gun at its future position. Video Subsystem Jaime Lien Overview The video subsystem is responsible for receiving the analog composite video signal from the NTSC camera and producing the target’s position coordinates and speed. This system runs on a 10-MHz clock. The active video signal is sampled and converted to digital at a resolution of 80 by 60. At each of the 4800 sample points, the digital luminance value is compared to a threshold luminance value. The coordinates of points corresponding to whiteness are averaged at the end of each frame to determine the center of the target. Center coordinates from two consecutive frames are then used to calculate the person or object’s speed. The subsystem can be reset by the user via a push switch. During a reset, the system outputs position and speed values of zero. The block diagram for the video subsystem is shown in Figure 1. Hardware The composite video signal is fed into the following three hardware chips. GS4981 The GS4981, a video sync separator, is used to extract the vertical sync signal from the composite video. This signal pulses low at the end of each frame. LM311 The LM311 is a comparator that outputs a digital high or low if an input analog signal is above or below an input threshold voltage. Video horizontal and vertical retraces are hidden by surrounding the sync signals with a blanking period of pure black. Hence, a blanking signal signifies the beginning and end of each line of active video. Setting the LM311 threshold to 2.2 volts extracts the blanking signal from the composite video. AD775 This analog-to-digital converter samples the active video at 5 MHz in order to obtain digital luminance values. The reference ladder is set from 2.5 to 5 volts, biasing the converter to the active video voltage range. Because the luminance threshold is set in the middle of the active video, only the most significant output bit is used.Module Descriptions GS_LM The GS_LM module uses the synchronized vertical sync and blanking signals to determine the beginning of each frame and line. The output framestart and linestart signals pulse high for one clock cycle at their respective events. FSM and counters The FSM coordinates the sampling of the active video; the luminance comparison; and the operation of the position, center, and speed calculators. Its state transition diagram is shown in Figure 2. The sampling depends on inputs from two counters. The vertical counter sends a venable signal that allows the FSM to use every fourth line of video, or 60 lines per frame. Venable is also used to reset the horizontal counter, which sends a high henable signal to the FSM after every six cycles of a 10-MHz clock, or 80 times per line. Together, venable and henable produce a resolution of 80 by 60. The henable signal causes the FSM to accept the luminance value from the A/D converter. If the luminance for a given sample is determined to be white (i.e. the AD775’s most significant output bit is 1), the FSM allows the center calculator to accumulate the position coordinates corresponding to the sample. It then increments the position calculator and waits for the next henable. After the last sample of the line, the position calculator returns an xdone signal to the FSM, causing it to wait for


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MIT 6 111 - Video Track and Shoot System

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