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Audio Impedance Meter

Audio Impedance Meter. 70.7 V 150 20 º . Mode. Select. On Off. Team Leader Kendrick Taylor Group Members Terrence Carter Keithric Taylor Milton Naylor. Design Team Advisor Dr. Noel Schulz Sponsor Mr. Martin F. Jue (MFJ Enterprises).

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Audio Impedance Meter

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  1. Audio Impedance Meter 70.7 V 15020º  Mode Select On Off

  2. Team Leader Kendrick Taylor Group Members Terrence Carter Keithric Taylor Milton Naylor Design Team Advisor Dr. Noel Schulz Sponsor Mr. Martin F. Jue (MFJ Enterprises) Design Team Members

  3. Abstract We plan to design a digital impedance meter that will be used during installation and for troubleshooting of speaker systems. This handheld device will display the measured impedance, power, and voltage of a speaker system.

  4. Problem Statement • Speaker systems are used throughout the world, so it is important that they are installed properly. • It is essential that the impedance ratings on the amplifier and speakers match.

  5. Problem Statement (Cont.) If the wrong impedances are presented to the amplifier, the following problems can arise: • Damage to the amplifier • Damage to the speaker • Inefficient operation • Uneven sound distribution • Distorted sound

  6. Solution A low cost, portable impedance meter. A handheld digital impedance meter will give the system installers the required device to match the impedances of the speakers and the amplifier.

  7. Implementation Audio Power Amplifier Speaker System 70.7 V 15020º  Speaker System Mode Select On Off

  8. User-Interface • The LCD shows the user both the Impedance and calculated value. • Mode button switches between Impedance mode and Calculator mode. • Select button toggles between input values. 70.7 V 15020º  Calculator P (Watts) V (Volts) 0000 0000 Mode Select On Off

  9. Design Constraints • Measurement Ranges • 5 - 200 k impedance range • 25, 50, 70.7, 100 volt speaker system • Internal Calculator • Calculates power and voltage • Voltage Requirement • 9V Battery • Filter • Converts 1kHz PWM to a 1kHz sine wave

  10. Design Constraints (Cont.) • Driver Amplifier • Increases the signal to 5 volts • Connections • Two 15” test leads with alligator clamps • Weight • Less than 2 pounds • Packing Size • 6’’ x 4’’ x 2’’ (L x W x H)

  11. Hardware Block Diagram Data PIC Active Filter Driver Amplifier Rectifier LCD Power Supply

  12. PIC Data -Pulse-width modulation 1 kHz signal -Controls LCD PIC Active Filter LCD Display Voltage

  13. PIC (Cont.) • The type of PIC used will be the PIC16C63. • Use voltage measurements to solve for the unknown impedance • Generates 1 kHz PWM

  14. Functional Diagram PIC Active Filter

  15. Active Filter Opamp LM324 Bandpass Filter • Center frequency of 1kHz • Multiple feedback • Eliminate harmonics

  16. Active Filter (Cont.)

  17. Functional Diagram PIC Active Filter Driver Amplifier

  18. Driver Amplifier Class-A Low-Power • Increases the incoming signal to 5 volts and power to 1 watt • Drives the signal through the impedance load

  19. Functional Block Diagram PIC Active Filter Driver Amplifier Rectifier

  20. Rectifier Circuit • AC – DC conversions • Schottky Diode • Half-wave rectifier • Voltage outputs are relayed back to the PIC

  21. Power P = V2/Z Voltage V = (P*Z) Magnitude of Impedance Z = Xs (Vz/Vs) Phase of Impedance Sin  = (Vin2 -Vs2 - Vz2) (2*Vs*Vz) Calculations Performed by PIC

  22. Functional Diagram PIC Active Filter Audio Driver Amplifier Rectifier LCD

  23. Summary • Digital handheld device • Installing and troubleshooting speaker systems • Impedance Measurement • Displayed in polar form • Internal Calculator • This unit calculates a power value based on impedance and voltage, or calculates a voltage value, based on impedance and power.

  24. Questions ???

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