- Archana Venkataraman - i A Two-Input Polygraph 6.111 – Introductory Digital Systems Laboratory Final Project Archana Venkataraman, Christopher Buenrostro, Isaac Rosmarin TA: Theodoros Konstantakopoulos May 18, 2006 Abstract A two-input polygraph was implemented on the Xilinx Virtex2 FPGA. The system relied on physiological data in the form of skin conductivity and pulse rate, and made a binary decision as to whether or not the subject is lying. The project was divided into three portions. The first part consisted of designing and implementing the physiological sensors. The second part functioned as the main digital control unit for the system. The final portion was the output display which displayed both dynamic data as well as the T/F decision. Due to the modularity of the design, each of the portions were designed and implemented individually. Integrating the system, therefore, posed few problems. Although the digital part of the system functioned correctly, the lie detector could not be tested very effectively due to the poor quality of the sensor data.- Archana Venkataraman - ii Acknowledgements: Before launching into our project details, there are several people that we need to thank for a wonderful semester and without whose help we all would have finished the course just a little more sane a sleep-deprived. First and foremost, we would like to thank Professor Chandrakasan and his unbounded enthusiasm for all things digital. His lectures were always informative, and he was always available for help, especially during hectic times before assignments were due. We would also like to thank our wonderful TA’s Theodoros, Jae, and Javier for all their help late at night in lab. We would also like to thank our lab assistant Gim Hom for yet another semester devoted to course 6 students. He was always knowledgeable and helpful when it came to debugging code that really should work, but for some reason kept crashing. Last, but not least, we would like to thank Nigel for giving us (well, just Archana) unwavering support through all those hectic hours in lab. His compassion was much appreciated, especially since ModelSim does not share his attitude of thoughtfulness and helpfulness.- Archana Venkataraman - iii Table of Contents 1.0 - Introduction and System Overview………………………………………………………….1 2.0 – The Physiological Sensors…………………………………………………………………..3 3.0 – The Digital Control Unit…………………………………………………………………….7 3.1 – Design Considerations………………………………………………………………7 3.2 – Module Descriptions………………………………………………………………...9 3.2.1 – The User Capture Block…………………………………………………...9 3.2.2 – The Memory Module……………………………………………………...9 3.2.3 – The Digital Decision-Making Unit………………………………………10 3.3 – Testing and Debugging the System………………………………………………..12 4.0 – The Video Display…………………………………………………………………………13 5.0 – Connecting and Debugging the Entire System…………………………………………….18 List of Figures Figure 1.1 – Block Diagram of the Overall Lie Detector System………………………………...2 Figure 2.1 – Hardware Block Diagram……………………………………………………………3 Figure 2.2 – Electrocardiogram Generator………………………………………………………..4 Figure 2.3 – Skin Conductivity Detector………………………………………………………….4 Figure 2.4 – Analog-to-Digital State Transition Diagram………………………………………...5 Figure 2.5 – RAM State Transition Diagram……………………………………………………...6 Figure 2.6 – Recorder State Transition Diagram………………………………………………….6 Figure 3.1 – Block Diagram of the Digital Control Unit………………………………………….8 Figure 3.2 – State Transition Diagram for Major FSM in Memory Module…………………….10 Figure 3.3 – State Transition Diagram for Major FSM in DDMU………………………………11 Figure 4.1 – Block Diagram of the Video Display………………………………………………13- Archana Venkataraman - 1 1.0 – Introduction and System Overview In this project a two-input polygraph was implemented using the Xilinx Virtex2 FPGA. The physiological inputs used are pulse rate and skin conductivity. These signals were chosen because they are fairly easy to measure and interpret. During times of emotional stress, such as when the subject is made uncomfortable and forced to lie, the pulse rate increases. Likewise, the subject is more likely to sweat, which increases his or her skin conductivity. The project is divided into three portions: the analog sensors to measure skin conductivity and pulse, the digital control unit, and the output display. The two sensors were implemented on a breadboard using analog circuitry. The schematics for these circuits are shown in section 2. The ADC0804 was used to convert the analog signal into a digital one, which was then stored in the main memory. The Digital Control Unit forms the backbone of the lie detector by integrating the digital data acquisition, data processing, and system control signals. It has three major roles in the overall system. First, it captures and registers user input signals. This is implemented in a manner similar to the Walk Register in the Traffic Light Controller lab. Second, it controls the sequence of reads and writes of the sensor data to the main memory. Since it is the only module which controls reading and writing, data acquisition becomes easier and more straightforward. Lastly, the Digital Control Unit implements the decision algorithms which output a binary T/F decision as to whether or not the subject is lying. The video display portion of the project serves two purposes. First, it communicates the result of the algorithm’s decision to the user. Secondly, it displays the
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