Audio Impedance Meter

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Audio Impedance Meter
 
 
70.7 V 150?20º
?
Mode
Select
On Off
2
Design Team Members

• 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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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.

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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.

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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

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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.

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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

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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)

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Hardware Block Diagram
Data
PIC
Active Filter
Driver Amplifier
Rectifier
LCD
Power Supply
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PIC
Data
-Pulse-width modulation 1 kHz
signal -Controls LCD
PIC
Active Filter
LCD Display
Voltage
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PIC (Cont.)

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

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Functional Diagram
PIC
Active Filter
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Active Filter

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

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Active Filter (Cont.)
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Functional Diagram
PIC
Active Filter
Driver Amplifier
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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

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Functional Block Diagram
PIC
Active Filter
Driver Amplifier
Rectifier
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Rectifier Circuit

• AC DC conversions
• Schottky Diode
• Half-wave rectifier
• Voltage outputs are relayed back to the PIC

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Calculations Performed by PIC

• Power
• P V2/Z
• Voltage
• V ?(PZ)

• Magnitude of Impedance
• Z Xs (Vz/Vs)
• Phase of Impedance
• Sin ? (Vin2 -Vs2 - Vz2)
• (2VsVz)

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Functional Diagram
PIC
Active Filter
Audio Driver Amplifier
Rectifier
LCD
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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.

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Questions

• ???