Design Document for Audio Impedance Meter Submitted to: Professor Joseph Picone ECE 4512: Senior Design I Department of Electrical and Computer Engineering Mississippi State University Mississippi State, Mississippi 39762 April 29, 2003 Submitted by: Kendrick Taylor, Terrence Carter, Keithric Taylor, Milton Naylor Faculty Advisor: Dr. Noel Schulz Department of Electrical and Computer Engineering Mississippi State University Box 9571 Mississippi State, MS 39762 Email: {(kjt6, tcc3, kjt7, mln6) @msstate.edu}Impedance Meter ECE 4512 April 29, 2003 TABLE OF CONTENTS 1. PROBLEM STATEMENT…………………………………………………………………...1 2. OBJECTIVES………………………………………………………………………………...3 2.1 Impedance and Voltage Ranges………………………………………………….4 2.2 Mathematical Ablility………………………………………………………………..5 2.3 Test Frequency, Active Filter, and Constraints………………………………….5 2.4 Operating Temperature…………………………………………………………….5 2.5 Power Source, Packing Size, and Cost…………………………………………..5 3. APPROACH…………………………………………………………………………………..6 3.1 Introduction………………………………………………………………………….6 3.2 Software Components……………………………………………………………...7 3.2.1 PIC…………………………………………………………………………7 3.2.2 Software Engineering…………………………………………………….8 3.3 Hardware Components……………………………………………………12 3.3.1 Active Filter………………………………………………………………12 3.3.2 Amplifier………………………………………………………………….15 3.3.3 Rectifier…………………………………………………………………..16 4. TEST SPECIFICATIONS………………………………………………………………….19 4.1 Test Equipment and Software……………………………………………………19 4.2 System Testing…………………………………………………………………….20 5. TEST CERTIFICATION…………………………………………………………………....24 5.1 Simulation………………………………………………………………………….24 5.1.1 PIC………………………………………………………………………..24 5.2 Hardware…………………………………………………………………………...27 5.2.1 Active Filter………………………………………………………………27 5.2.2 Amplifier………………………………………………………………….28 5.2.3 Rectifier…………………………………………………………………..29 5.2.4 System Tests…………………………………………………………….29 6. SUMMARY AND FUTURE WORK……………………………………………………….30 7. ACKNOWLEDGEMENTS…………………………………………………………………30 8. REFERENCES……………………………………………………………………………...31Impedance Meter ECE 4512 April 29, 2003 EXECUTIVE SUMMARY Many individuals have home entertainment centers that utilize speaker systems. For speakers to produce quality sound, it is important that the impedance ratings on the amplifier and speaker system matched. A handheld digital impedance meter will provide the sound system installers with the perfect tool to match the impedance of the speakers and the amplifier. If their impedance values are matched, the sound will be optimized and produce less distortion [1]. Our device will be designed to measure impedance ranges between 5 and 200 kΩ and calculate the power of 25, 50, 70.7 or 100-volt systems. The device will use a 1 kHz signal to perform all of its measurements. This specific frequency was chosen because it is within the range of the standard audio frequency [2]. This device will function using an active filter, an amplifier and a rectifier. The filter will convert an input pulse width modulated wave to a sine wave. Once the signal passes through the filter, the output voltage will be lower than the input voltage. Therefore, an amplifier will be used to step the voltage coming out of the filter back up to 5 volts. Finally, a rectifier will be used to convert the voltage from AC to DC. Our meter will be connected to the speaker line just as an amplifier would. After the impedance measurements are taken, that value can be used to troubleshoot the system and either pinpoint the speakers as the problem or eliminate them as the problem. Our device should cost no more than 300 dollars and weigh no more than two pounds, which is competitive with other devices on the market. Our device will measure the impedance of standard systems, including 70.7-volt systems, which are standard in the United States [3]. We will use a PIC to produce the desired wave, as well as perform all of our calculations. This PIC will be programmed using C++. The PIC will generate a 1 kHz pulse-width modulation signal to the active filter. The active filter has been tested and converts this signal from a 1 kHz-input wave to a sine wave. This desired result has been confirmed using P-SPICE and actual bread boarded tests. We are inputting a square wave from the Function Generator to our filter design, and getting the desired sine wave. We have used the oscilloscope to confirm the results. This sine wave will be passed through the amplifier, which will in turn amplify the voltage of the signal leaving the filter to 5 volts. The amplifier has also been tested using P-SPICE simulations and in lab implementations. The voltage is also being amplified as desired. The rectifier circuit will convert voltage signals from AC to DC. The rectifier is still in the process of being implemented using P-SPICE. The DC signals will be relayed back to the PIC so it can perform the calculations for the device. The audio impedance meter will be an
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