MUSCLE STRENGTH CIRCUIT

1
MUSCLE STRENGTH CIRCUIT

• Siddharth Lohia
• Group 2
• ECE 445
• Summer 07

2
Introduction

• A Circuit to measure applied force and convert
  the force into meaningful output
• Two main features of the circuit are current
  output and output display
• The current output is stable across a range of
  load
• The amount of current per amount of force is
  easily adjustable by just a screwdriver

3
Additional Features

• Display
• The user can define the minimum and maximum range
  of input force
• The Screen shows the current force and also
  holds the maximum force until the user resets it
• The input force can be linearly scaled to the
  output value by any factor
• The Output can be in any dimension

4
Hardware

• Load Cell
• Filter
• Voltage Amplifier
• Current Transmitter

5
Load Cell

• Dinamica Generale
• DG-SP1
• 88 lbs Capacity
• 2mV/V output
• For 12 V power supply the output is in the range
  of 0-24 mV

6
Filter
The frequency of noise from the Load cell output
is 215.52 kHz
7
Filter Schematic
8
Filter Equations

• Calculation of Cutoff Frequency
• 1 / ( 2pi RC) 1/ ( 2 3.14 1000 .001u )
  159,154.94 Hz
• 160 kHz
• 1 / ( 2pi RC) 1/ ( 2 3.14 1000 .002u )
  318,309.88 Hz
• 320 kHz
• Zeroes in on the 215 kHz noise frequency
• Improvement in signal stability observed

9
Voltage Amplifier

• AD708 Ultra low Offset Voltage Dual Op Amp
• Differential amplification of Load Cell Output
• Gain Controlled by potentiometer knob
• The gain is between 30 and 100
• Although the gain can be adjusted to be up till
  350, the current transmitter will burn out at
  such high input voltages

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Amplifier Schematic
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Op Amp Equation and Data

• Gain 1 210k/ ( 56 R4)
• For R4 163.2 O , Gain 91.24
• Actual Data collected for R4 163.2 O

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Current Transmitter

• AD 694 4- 20 mA current range
• Converts input voltage into a current over
  desired range
• The current output is independent over resistor
  range of 20 O to 400 O
• Calculated from the equation ( Vsrc 2.5) / 20m,
  where Vsrc is 12 V
• An easy way to increase the value of load
  resistance is to increase the Vsrc of Current
  Transmitter

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Transmitter Schematic
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Configuration of the transmitter

• The V ( A-B ) output from AD 708 is buffered by a
  20k resistor, and fed into the signal and
  signal inputs respectively.

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Current Output Voltage Input
For Load 19.8 O
For load 384 O
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Force Input to Current Output
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Software

• HIO 010 Prizm V.3 software used for programming
  the HIO device
• GUI for screen displays
• Ladder Structure Programming for storing and
  displaying the maximum value

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GUI Screenshot
19
A/D conversion
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Partial Code for Displaying max. Force
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Equation For Display

• Slope lbs/mA Load Range / Current range (In
  the application zone for max. accuracy)
• Hi Set lbs Slope 16
• Lo Set lbs 0 for max. range
• (since the max input is 20 mA and the min input
  is 4 mA)
• now 4 mA corresponds to 0 force and 20 mA
  corresponds to Hi Set.

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Current Output For Display Configuration
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Uses With Display

• Measure Push Pull Strength.
• Two Such Devices can be used to detect muscle
  imbalances in a Chiropractor Clinic setting.
• Measure and record maximum force applied when
  working in a gym.

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Uses Without Display

• The Force can be calibrated to output any desired
  current in the 4-20 mA range.
• The Current Loop can be used for operations like
  prosthetic devices.
• It can be used for devices that require a stable
  power supply over a broad range of application of
  load.

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SWOT Analysis
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Credits

• Mr. Craig Zeilenga from the Machine Shop
• Prof. Gary Swenson
• Mr. Tony Mangognia