Biomechanics Gait Analysis Lab - Biomedical Engineering ...

Biomechanics Gait Analysis Lab
Operator’s Manual
By
Kimberly Carr, Omar Chawiche, Angela Ensor
Team 3
Client Contact:
David Kaputa &
Dr. John D. Enderle
University of Connecticut
Biomedical Engineering Department
Bronwell Building, Room 217C
260 Glenbrook Road
Storrs, Connecticut 06269-2247
Phone: (860) 486-5521
Page 1

IMPORTANT SAFETY INSTRUCTIONS
Accurate gait measurements from the footswitch and FSR
insoles can be obtained reliably when done properly.
Please read the appropriate sections of the Biomechanics
Gait Analysis Laboratory Owner’s Manual thoroughly before
performing any of the laboratory exercises.
1. Do not tamper with the transmitter or receiver. Any
tampering with the contents of these devices may
damage the quality of the data transmission/reception.
2. Do not leave the transmitter and receiver powered on
for long periods of time when they are not in use.
This will drain the batteries of their charge.
3. Do not tamper with the footswitch or FSR insoles. Any
tampering with the contents of these devices may
damage the sensors as well as the quality of data
measurements.
4. Make certain that the 5-pin LEMO male connector from
the footswitch insole and 4-pin LEMO male connector
from the FSR insole are inserted into the counterpart
LEMO female connectors correctly (make sure to line up
the red dot on the male to the red area on the
female).
5. Ensure the footswitch or FSR insole is placed
correctly inside of the Subject’s shoe or taped to the
bottom of the Subject’s foot.
6. When performing either the FSR or footswitch insole
laboratory exercise, be sure to shorten and secure the
connector cables to avoid a tripping hazard.
7. Only insert the appropriate 9 Volt and 3 Volt
batteries into the transmitter.
8. Do not alter the footswitch or FSR data analysis
LabVIEW program.
9. Be sure to properly connect the footswitch data wires
from the receiver into the digital data inputs and the
FSR data wires into the analog data inputs on the
National Instruments BNC-2021 device.
Page 2

PARTS AND ACCESSORIES
The following parts and accessories are included with the
Biomechanics Gait Analysis Laboratory:
• Owner’s Manual
• Black Adjustable Fanny Pack
• 2 Male, Size 9, Footswitch Insoles (Right and Left)
• 2 Female, Size 7, Footswitch Insoles (Right and Left)
• 2 Male, Size 9, FSR Insoles (Right and Left)
• 2 Female, Size 7, FSR Insoles (Right and Left)
• Black Transmitter Box
• Black Receiver Box
• 2 Nine Volt Batteries
• 2 Three Volt Lithium Batteries
• National Instruments PXI-1031 device equipped with
PXI-8330 and PXI-6040E device cartridges
• National Instruments BNC-2120 device
• 3 National Instruments LabVIEW Computer Programs:
1. Gait Analysis Footswitch Insoles System
2. Men’s Force Sensitive Resistor (FSR) Insoles System
3. Women’s Force Sensitive Resistor (FSR) Insoles System
Page 3

FEATURES
The Biomechanics Gait Analysis Laboratory offers a variety
of useful features for analyzing a Subject’s gait.
Such features include:
• Innovative force sensitive resistor (FSR) insoles
• Wireless transmission of total gait cycle data.
• Compact and portable design
• Original National Instruments LabVIEW computer
programs
• Capable of calculating the following gait parameters:
Footswitch Insoles
‣ total gait cycle duration
‣ stance phase duration
‣ swing phase duration
‣ time of toe contact
‣ time of 1 st metatarsal contact
‣ time of 5 th metatarsal contact
‣ time of heel contact
‣ total gait cycle length
‣ stance phase length
‣ swing phase length
‣ % of time on toe during stance phase
‣ % of time on 1 st metatarsal during stance phase
‣ % of time on 5 th metatarsal during stance phase
‣ % of time on heel during stance phase
‣ cadence
‣ total gait cycle velocity
‣ stance phase velocity
‣ swing phase velocity
FSR Insoles
‣ weight distribution on toe during stance phase
‣ weight distribution on heel during stance phase
Page 4

Table of Contents
Section
Page Number
Important Safety Instructions 2
Parts and Accessories 3
Features 4
Table of Contents 5
1.Introduction 6-31
1.1 General Overview of Device 6-19
1.2 Instructions for Using the Biomechanics
Gait Analysis System
20-31
1.2.1 Instructions for Footswitch Insoles 20-28
1.2.2 Instructions for FSR Insoles 28-31
2. Maintenance 32-41
3. Technical Description 42-62
4. Troubleshooting 63-77
Page 5

1. Introduction
1.1 General Overview of the Device
The Biomechanics Gait Analysis Laboratory (Figure 1)
represents the upgraded gait analysis laboratory for use in
the University of Connecticut’s Biomechanics Course. The
upgraded lab will allow the student to gain a more hands on
understanding of the hardware and applications of gait
analysis, similar to the features found in a clinical
setting of a gait analysis laboratory.
Footswitch Insole
FSR Insole
Transmitter
Receiver
NI PXI-1031
NI BNC-2120
Footswitch
LabVIEW Program
FSR
LabVIEW Program
Figure 1: Complete Biomechanics Gait Analysis System
Page 6

The new laboratory utilizes a number of different devices
including footswitches insoles, force sensitive resistor
(FSR) insoles, National Instruments devices, along with
three National Instruments LabVIEW computer programs, that
work together to measure the following gait parameters:
‣ total gait cycle duration
‣ stance phase duration
‣ swing phase duration
‣ time of toe contact
‣ time of 1 st metatarsal contact
‣ time of 5 th metatarsal contact
‣ time of heel contact
‣ total gait cycle length
‣ stance phase length
‣ swing phase length
‣ % of time on toe during stance phase
‣ % of time on 1 st metatarsal during stance phase
‣ % of time on 5 th metatarsal during stance phase
‣ % of time on heel during stance phase
‣ cadence
‣ total gait cycle velocity
‣ stance phase velocity
‣ swing phase velocity
‣ weight distribution on toe during stance phase
‣ weight distribution on heel during stance phase
The footswitch insoles were purchased from B&L Engineering
based out of Tustin, California (Figure 2)
Figure 2: B&L Engineering Footswitches
Page 7

The footswitches are to be worn as insoles in the Subject’s
shoes or taped to the bottom of their bare feet. The
footswitches will indicate the total time each foot is and
is not bearing weight. The footswitches have contact areas
in the Heel, Fifth Metatarsal, First Metatarsal, and Great
Toe areas, to indicate when these areas of the foot are
bearing weight (Figure 3).
Figure 3: Footswitch Contact Areas
The force sensitive resistor (FSR) insoles (Figure 4) were
constructed using force sensitive resistor sensors from
Tekscan, SOF® Comfort Insoles, black Gorilla tape, and ACE
Red 1/16” Sheet Rubber.
Page 8

Figure 4: FSR Insole
The FSR’s are to be worn as insoles in the Subject’s shoes
or taped to the bottom of their bare feet. The FSR’s will
indicate the weight distribution on the toe and heel during
the stance phase of the gait cycle. The FSR’s have contact
areas in the Heel and Great Toe areas, to indicate the
applied pressure on these areas (Figure 5).
Left Insole
Design
Bottom Layer
Top Layer
Rubber
FSR
Insole
Duct Tape
Lead Wires
FSR
Figure 5: FSR Contact Areas
Page 9

To send the data from the footswitches and FSR insoles to
the computer, a telemetry system was developed. The
transmitter (Figures 6-8) uses a 418 MHz frequency to
transmit the data from the insoles to the receiver (Figure
9-11).
Figure 6: Transmitter Schematic
Figure 7: Transmitter PCB and Components
Page 10

Figure 8: Transmitter Box
Figure 9: Receiver Schematic
Page 11

Figure 10: Receiver PCB and Components
Figure 11: Receiver box
Page 12

The receiver connects directly to the National Instruments
BNC-2120 device (Figure 12), which is connected to the
National Instruments PXI-1031 (Figure 13) device through
the PXI-6040E device cartridge.
Figure 12: National Instruments BNC-2120 device
Figure 13: National Instruments PXI-1031 device
Page 13

The National Instruments PXI-1031 device is then directly
connected to the computer through the PXI-8330 device
cartridge.
To analyze the data from the footswitch and FSR insoles in
real-time, three LabVIEW computer programs were developed
(Figures 14-19).
Figure 14: Footswitch Insoles LabVIEW Program Front Panel
Page 14

Figure 15:Footswitch Insoles LabVIEW Program Block Diagram
Page 15

Figure 16: Men’s FSR Insoles LabVIEW Program Front Panel
Page 16

Figure 17: Men’s FSR Insoles LabVIEW Program Block Diagram
Page 17

Figure 18: Women’s FSR Insoles LabVIEW Program Front Panel
Page 18

Figure 19:Womens FSR Insoles LabVIEW Program Block Diagram
Page 19

1.2 Instructions for Using the Biomechanics Gait
Analysis Laboratory System
1.2.1 Instructions for Footswitch Insoles:
1. Place the footswitch insole inside of the Subject’s shoe
(Figure 20) or tape it securely to the bottom of their
foot.
Figure 20: Footswitch Insole
2. Place the transmitter box into the black fanny pack
(Figure 21).
Figure 21: Transmitter Box in Fanny Pack
Page 20

3. Place the fanny pack around the Subject’s waist (Figure
22).
Figure 22: Placement of Fanny Pack
4. Tighten the fanny pack strap to secure the transmitter
into place (Figure 23).
Figure 23: Tighten Fanny Pack Strap
Page 21

5. Connect the 5-pin male LEMO connector from the
footswitch insole properly into the female connector on
the transmitter box (Figure 24); make sure to match up
the red areas.
Figure 24: Footswitch Connection to Transmitter Box
6. Zip-up the fanny pack until the transmitter is fixed
into place.
7. Connect the footswitch output data wires from the
receiver box to the National Instruments BNC-2120 device
digital I/O ports. Connect the white ground wire to the
D GND input, blue Toe data wire to the P.0.0 input, blue
1 st Metatarsal wire to the P.0.1 input, blue 5 th
Metatarsal wire to the P.0.2 input, and blue Heel wire
to the P.0.3 input using a screw driver to secure them
into place (Figure 25).
Page 22

Figure 25: Footswitch Output Wire Connection
8. Mark a start line on the floor where the subject’s heel
will first make contact.
9. Turn ON the Transmitter and Receiver boxes (Figure 26).
Page 23

Figure 26: Telemetry ON/OFF Switch
10. Open the Gait Analysis Footswitch Insoles System
LabVIEW Program (Figure 14).
11. Run the LabVIEW program.
12. Press the ON button in the block diagram to start
footswitch data collection.
13. Have the Subject walk one complete gait cycle, heel to
heel of same foot (Figure 27). When pressure is applied
to a sensor, the graph for that sensor should change
from 0 to 1.
Figure 27: Complete Gait Cycle
Page 24

14. Press the OFF button on the block diagram to end
footswitch data collection and press the stop button to
end the LabVIEW program.
15. Turn OFF the transmitter and receiver boxes.
16. Measure the distance (m) from the start line on the
floor to the subject’s heel after the complete gait
cycle (Figure 28).
Figure 28: Measure Total Gait Cycle Length
17. Open up the Toe, 1 st Metatarsal, 5 th Metatarsal, and Heel
LVM files in Microsoft© Excel (Figure 29). Delete the
entire 1 st and 3 rd column of zeroes, so that you have the
sensor data in the 1 st column and the time data in the
second. Change the time data column format so that the
values are displayed as a number value, not a scientific
one (Figure 30).
Page 25

Figure 29: Original Toe Sensor Data File
Page 26

Figure 30: Corrected Toe Sensor Data File
Page 27

18. In this chart, the 1 st column is the sensor data, when
pressure is applied to the sensor the output is 0 and
when no pressure is applied to the sensor the output is
-1. From this information, input the following values
into the footswitch data area of the LabVIEW program
front panel (blue = input values, black = output
values):
‣ Time @ First Toe Contact
‣ Time @ Last Toe Contact
‣ Time @ First 1 st Metatarsal Contact
‣ Time @ Last 1 st Metatarsal Contact
‣ Time @ First 5 th Metatarsal Contact
‣ Time @ Last 5 th Metatarsal Contact
‣ Time @ First Heel Contact
‣ Time @ First Heel Contact (Swing Phase)
‣ Time @ Last Heel Contact (Stance Phase)
‣ Total Gait Cycle Length
‣ Stance Phase Length/Shoe Size
19. Run the LabVIEW program.
20. Press the Calculate Footswitch Data button in the block
diagram.
21. Stop the LabVIEW program.
Footswitch Data Calculation Complete!
1.2.2 Instructions for FSR Insoles:
1. Place the FSR insole inside of the Subject’s shoe
(Figure 31) or tape it securely to the bottom of their
foot.
Figure 31: FSR Insole
Page 28

2. Place the transmitter box into the black fanny pack
(Figure 21).
3. Place the fanny pack around the Subject’s waist (Figure
22).
4. Tighten the fanny pack strap to secure the transmitter
into place (Figure 23).
5. Connect the 4-pin male LEMO connector from the FSR
insole properly into the female connector on the
transmitter box (Figure 32); make sure to match up the
red areas.
Figure 32: FSR Connection to Transmitter Box
6. Zip-up the fanny pack until the transmitter is fixed
into place.
Page 29

7. Connect the FSR output data wires from the transmitter
box to the National Instruments BNC-2120 device analog
inputs. Connect the blue Toe data wire from the
transmitter to the AI.0 input and the yellow Heel wire
to the AI.1 input using the appropriate connector cable.
Remember to connect the black alligator clips to ground
from the receiver box. (Figure 33).
Figure 33: FSR Output Wire Connection
Page 30

8. Mark a start line on the floor where the subject’s heel
will first make contact.
9. Turn ON the Transmitter and Receiver boxes (Figure 26).
10. Open either the Women’s Force Sensitive Resistor (FSR)
Insoles or Men’s Force Sensitive Resistor (FSR) Insoles
LabVIEW Program (Figures 16 & 18).
11. Press the button to True if the Subject is wearing the
left insole and leave it at False if the Subject is
wearing the right insole.
12. Run the LabVIEW program.
13. Have the Subject walk one complete gait cycle, heel to
heel of same foot (Figure 27).
14. Press the stop button to end the LabVIEW program.
15. Turn OFF the transmitter and receiver boxes.
16. Open up the Test data LVM file in Microsoft© Excel.
17. Record the maximum force exerted by the subject on the
toe and heel during the gait cycle.
FSR Data Calculation Complete!
Page 31

2. Maintenance
Battery life:
We have used two kinds of batteries in our project, the 3
volt lithium battery and the 9 volt battery (Figure 34).
Figure 34: Batteries Used in the Project
The lithium battery combines a very light weight material
with chemical features that make it suitable for the design
of high voltage batteries. It gives a virtually constant
voltage over the discharge period, allowing them to be used
in sensitive electronic equipment. The 3 volt lithium
batteries could last up to 10 years. Another advantage of
using this type of batteries is that, it could operate in a
wide range of temperature from -30°C to +60°C.
The 9v battery we used also has its advantages, it offers
the longest lasting power source of all primary batteries
over a range of sizes, and it can operate in a temperature
range between -30°C to 55°C.
Page 32

Battery Replacement
1. Turn both of the switches off
2. Open the top of the boxes using a screw driver.
Page 33

3. For the 3v lithium battery, pull up on one side of the
battery.
4. For the 9 volt battery pull up and backward, towards the
end part of the battery.
Page 34

5. Place the 3v lithium battery in the right orientation,
where the small circle is facing down, and place the cover
back on along with the screws.
6. Connect the 9v battery in correct orientation and place
the cover back on along with the screws.
Page 35

Static
Do not expose the boxes to static electricity. The
electrical components within the boxes are very sensitive
and you could possibly damage them.
Cleaning
- Turn the switch off
- Using a piece of soft cloth and surface cleaner,
wipe the dirty area of the case
Page 36

- Dry the cleaned area with a soft cloth
- Keep electrical leads clean
- Keep the boxes in a dust free environment.
Note:
- Avoid bending the pins on the male serial
connectors. Bending the pins will result in the
connector no longer fitting with the female one.
- Do not try to place foreign objects into the female
LEMO connector, because it will cause damage to the
connector.
Page 37

Environmental
1. Water:
Do not expose the transmitter/receiver boxes or any of the
other parts to water. This device is not water proof. If
exposed to water the device will be damage and should not
be turned on after for safety reasons.
2. Temperature:
- The device should not be exposed to high
temperature. That may cause damage to the device.
- The device should not be exposed to extreme cold
that could damage it.
- The device should be used in room temperature.
Page 38

3. Humidity
The device should not be exposed to high humidity that
could cause damage to it.
Page 39

Storage
The device should be stored at room temperature and under
the conditions stated before when not in use, preferably in
a storage closet.
Page 40

The footswitches and force sensitive resistor insoles are
made out of a layer of polyethylene-foam wrapped with black
Gorilla tape, making them waterproof and temperature
resistant to a certain degree.
Maintenance Overview
Do
• Keep electrical leads clean
• Keep the boxes in a dust free environment
• Avoid bending the pins on the male serial connectors
Don’t
• Expose the devices to high temperature
• Expose the devices to high humidity
• Expose the devices to water
• Expose the devices to static electricity
Page 41

3. Technical Description
The Biomechanics Gait Analysis Laboratory equipment
consists of Force Sensitive Resistor Insoles, Footswitch
Insoles, insole driver circuits, Telemetry devices, and
National Instruments BNC-2120 and PXI-6040E in the PXI-1031
box. The Force Sensitive Resistor Insoles and Footswitch
Insoles are powered through the drive circuit, which is
part of the transmitter telemetry device. The transmitter
device sends the signal to the receiver telemetry device,
which is connected to the BNC-2120. The BNC-2120 receives
analog or digital signals and relays the signals to the
PXI-6040E, which provides the data to the LabVIEW® software
program in a computer. Since the system begins with input
from the insoles, a detailed description of the insoles
will be given first, followed by the remaining equipment in
order as listed above.
Force Sensitive Resistor (FSR) Insoles
The FSR insoles are comprised of force sensitive resistors,
sandwiched between cut-to-size shoe insoles and taped
together with Gorilla brand duct tape. A diagram of an FSR
insole is shown in Figure 35. Rubber disks are placed on
either side of the sensing area to concentrate the force
directly onto the sensing area to provide a better reading,
which is indicated in Figure 36. The FSR has a three male
square pin connector, also shown in Figure 36 and Figure
35. The middle connector is connected to ground and the
two outer pins are used for the voltage supply input and
the voltage output. The two outer pins can be either used
as the input or the output. The force sensor is an
extremely thin, flexible printed circuit. The force sensor
is made of two layers of a polyester/polyimide substrate
sheet. For each layer, conductive silver is applied, on top
of which a layer of pressure-sensitive ink is applied. An
adhesive joins the two layers of substrate together to
complete the force sensor. The active sensing area is
outlined by the silver circle around the pressure-sensitive
ink, which can be seen in Figure 36. The silver lines
extend from the sensing area to the two outer connector
male square pins to form the leads.
Page 42

The sensors act as a force sensing resistors in an
electrical circuit, so that when it’s unloaded, the
resistance is quite high, and when it’s loaded, the
resistance is rather low. The resistance will vary as the
sensor is loaded and unloaded. Using a digital multimeter,
the resistance or force can be read by connecting the
probes to the outer two pins, and then apply a force to the
sensing area. The digital multimeter must be turned on and
the dial set to the resistance or voltage reading option.
The FSRs can range up to 1000 lbs by reducing the resistor
value and/or voltage of a driver circuit, which is used in
this design, shown in Figure 35, and will be described
next.
Left Insole
Design
Bottom Layer
Top Layer
Rubber Disks
FSR
Cut-to-size
shoe Insole
Duct Tape
Lead Wires
FSR
Figure 35: FSR Insole design
Page 43

Figure 36: FlexiForce FSR® (force sensitive resistor)
FSR Insole Driver Circuit
The output voltage from the force sensitive resistor is
relayed to the drive circuit, where it goes through three
inverting operational amplifiers (TL072), then run to the
microprocessor (PIC16F874), where it is converted from
analog to digital data before it can be transmitted via
telemetry. The FSR output voltage can range about 5V, but
the microprocessor can only receive up to 5V. In order to
make the FSR voltage output range between 0V-5V so the
microprocessor can receive the data, we need to use three
inverting operational amplifiers (TL072), which is show in
Figure 37. The inverting amplifiers require a +9V and –9V
power source in put at pins 8 and 4, respectively.
The first inverting amplifier consists of the force
sensitive resistor, with a varying resistance, and an
8.99KΩ reference resistor. This amplifier should have a
positive output voltage on pins 1 and 7. The second
inverting amplifier will have a 9.82kΩ input resistor and a
2.65kΩ reference resistor to give an inverse gain of -2.65.
This amplifier should have a negative output voltage on
pins 1 and 7. Then the third inverting amplifier will have
equally valued input resistor and reference resistor to
give a gain of -1, making the final inverse gain of the
last two inverting amplifiers 2.65. So, the final output
voltage should be positive on pins 1 and 7. Equations for
each inverting amplifier are given in Figure 39.
The input from the heel and toe sections of the FSR insoles
come into pins 2 and 6, respectively. The output to the
BNC-2120, described in the National Instruments section,
for the heel and toe comes from pins 1 and 7 on that last
inverting amplifier depicted in Figure 37.
In order to use telemetry for the FSR insoles, they must be
connected to the microprocessor through Pin 2 and Pin 3,
shown in Figure 38. The microprocessor requires a 5V power
source input at pin V DD . The microprocessor is capable of
Page 44

10-bit analog-to-digital conversion. Analog-to-digital
(A/D) conversion is the method of converting an analog
voltage into a discrete digital count of ones and zeros,
which can be transmitted by the telemetry system.
Unfortunately, due to changing our project, there was not
enough time in the last semester to troubleshoot the A/D
program part of the design, so it is not currently working.
Instead, the FSR insoles are connected directly to the BNC-
2120, through the transmitter box.
Page 45

Driver Circuit for FSR Insoles
Driver Circuit for
Footswitch Insoles
Figure 37: Transmitter Telemetry Device: Drive Circuit for FSR Insoles Outlined in Blue.
Footswitch Insoles in Green
Page 46

Figure 38: Microprocessor Circuit for FSR Insoles (PIC16F873)
Page 47

Equation for 1st Inverting Amplifier
V (RHeel)1 = -V FSR (R 6 /R FSR ) Eq.1
Equation for 1st Inverting Amplifier
V (RHeel)2 = -V (Rheel)1 (R 9 /R 8 ) Eq.2
Equation for 1st Inverting Amplifier
V (RHeel)3 = -V (Rheel)2 (R 13 /R 12 ) Eq.3
Definition of Variables
R FSR Force Sensitive Resistor
R All other resistors are numbered according to fig. 3.3
V (Rheel)X X represents output of matching inverting amplifier
Output Voltage from FSR
V FSR
Figure 39: Inverting Amplifier Equations as Shown in Figure
37
Shown in Figure 40, male 4-pin LEMO (FGG.0B.304.CLAD52Z)
connectors were used to connect the lead wires from the FSR
insoles to the transmitter box. The lead wires were
soldered into the holes, which can be seen in the rear view
drawing in Figure 40c.
A
B
C
D
Figure 40: Male 4-Pin LEMO Connector
The following table gives the dimensions for the LEMO
connector shown in Figure 40.
Page 48

Metric A L M S1 S2
mm. 9.5 35.0 25.0 8.0 7.0
in. 0.37 1.38 0.98 0.31 0.28
Table 1: Measurements for figure 3.6A
The male LEMO connector fits to the female LEMO connector
(ECG.0B.304.CLL), which is attached to the printed
circuited board in the transmitter box and shown in Figure
41 below.
A
B
Figure 41: Female LEMO Connector
The following table gives the dimensions for the LEMO
connector shown in Figure 41.
Metric A B e E L M N S1 S3
mm. 12.0 12.5 M9X0.6 5.5 20.7 2.5 19.1 8.2 11.0
in. 0.47 0.49 - 0.22 0.81 0.10 0.75 0.32 0.43
Table 2: Measurements for figure 41A
Calibrating the FSR Insoles
Devices that measure force require calibration, which is
the process by which force is related to the output voltage
as the resistance varies with changing force. Using the
Tinius Olsen machine in compression, the following is the
procedure for calibration and requires two people to
perform.
1. Place one half of an insole between two hard plastic
plates
2. Place them between the two grips on the Tinius Olsen
machine and a pad in the larger empty spaces, so
pressure is applied evenly.
Page 49

3. Make sure that the sensor end of the FSR is in the
middle of the grips, for even force application.
4. Set-up two speeds on the Tinius Olsen machine, speed 1
at 0.01 and speed 2 at 0.005 (see manual for Tinius
Olsen machine to set-up speeds)
5. Hook up the insole to the transmitter telemetry
device, attach probes from a digital multimeter to the
output of the receiver box, and turn on both telemetry
boxes.
6. On person starts speed 1, and calls out the force
every 10 lbs starting at 40 lbs, while the other
person writes down the output voltage reading. At 200
lbs select speed 2, and continue until 350 lbs is
reached.
7. Turn all devices off when done
From this data determine the FSR resistance value at each
voltage reading, using the equations in Figure 39, and
divide the resistance by 1 to get conductance. Using the
conductance data and its matching force output, plot
conductance vs. force in Excel and use linear regression to
extrapolate the equation that will relate output force to
conductance.
Footswitch Insoles
The footswitch insoles consist of four compression closing
switches, at the heel, 1 st metatarsal, 5 th metatarsal, and
toe, as shown in Figure 42. These switches act as an open
or closed electric circuit, which requires an input of 5
volts. When pressure is applied to the switches, two
rubber cylinders contact pieces of brass sheets on each
side of the insole, which acts to close the electric
circuit, as shown in Figure 43. The only information that
this will provide is that pressure is being applied and the
length of time that pressure is applied. This will not
show variations in applied pressure. The footswitches can
provide velocity, cadence, stride length, and information
on gait cycle, single limb support, swing, and stance. The
footswitches do not need to be calibrated, which is a
difficult and lengthy process.
The drive circuit for the footswitch insoles is simply a
+9V battery connected to a voltage regulator to reduce the
input voltage to +5V, which is shown in Figure 37. The
footswitches are connected to the transmitter with a pulldown
resistor in between. The pull-down resistor is need
Page 50

to supply a very small voltage (less than 0.01V) because
the transmitter cannot process no input and would send a
default number which causes the program to give erroneous
outputs. The pull down resistor set-up is shown in Figure
44.
Fore Foot
Width
Great Toe
5 th Metatarsal
1st Metatarsal
Great Toe
Left Heel
1st Metatarsal
5th Metatarsal
Footswitch
Length
Heel Width
RightHeel
Figure 42: Footswitch diagram
Page 51

No current
Open Circuit
(No Pressure Applied)
Closed Circuit
(Pressure Applied)
Figure 43: Open and Closed Circuit diagram
Footswitch Input
10kO
DC
Output to Transmitter
Figure 44: Pull-Down Resistor Set-up
The LEMO connectors for the footswitches are similar to the
FSR insoles, except they have five pins instead of four.
The footswitches were purchased from B&L Engineering and
came with the male LEMO connectors attached. The male LEMO
connector (FGG.0B.305.CLAD52Z) is shown in Figure 45.
Page 52

A
B
C
D
Figure 45: Male LEMO Connector
The following table gives the dimensions for the LEMO
connector shown in Figure 45.
Metric A L M S1 S2
mm. 9.5 35.0 25.0 8.0 7.0
in. 0.37 1.38 0.98 0.31 0.28
Table 3: Measurements for Figure 45A
The female LEMO connector was soldered to the printed
circuited board in the transmitter box and is shown in
Figure 46. The layout for the lead input is shown in
Figure 47, which shows the sections of the foot coming into
each pin as well as the input voltage.
A
B
Figure 46: Female LEMO Connector
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The following table gives the dimensions for the LEMO
connector shown in Figure 46.
Metric A B e E M Nmax S1 S3
mm. 12.0 12.5 M9X0.6 2.4 2.5 18.3 8.2 11.0
in. 0.47 0.49 - 0.09 0.10 0.72 0.32 0.43
Table 4: Measurements for Figure 46A
Common (V o
)
Heal
5 th Metatarsal
Toe
1 st Metatarsal
Figure 47: Female LEMO Lead Wire Layout
Telemetry
The purpose of telemetry is to reduce the amount of wires
and allow the freedom of movement that cannot be achieved
using wires that are directly connected to a computer. The
telemetry system is comprised of a transmitter box and
receiver box. The transmitter box includes the 418MHz
transmitter/encoder chip (TXE-418-KH), 10-pin dip switch
(SDA10H1KD), and 418MHz Splatch antenna (ANT-418-SP-1),
which is shown in Figures 48-49. The box also has the
circuitry that provides the data to be sent wirelessly.
The receiver box has a 418MHz receiver/decoder chip (RXE-
418-KH), 10-pin dip switch (SDA10H1KD), and 418MHz Splatch
antenna (ANT-418-SP-1), which is shown in Figures 50-51.
The receiver/decoder chip is also wired to connect to the
BNC-2120, which will be described later in the National
Instruments equipment section. The transmitter/encoder and
receiver/decoder are powered by a 3V coin battery at pin 5
for both chips.
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Telemetry: Transmitter Set-up
Figure 48: Transmitter Circuit Schematic
Page 55

Figure 49: Transmitter PCB Schematic
Page 56

Figure 50: Receiver Circuit schematic
Page 57

Figure 51: Receiver PCB Schematic
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The 418MHz transmitter/encoder chip and Splatch antenna was
purchased from Linx Technologies and are shown in Figure
52. The transmitter receives the analog data and evaluates
it using binary, true or false, assessment, which
determines if it’s receiving a signal or not. The
evaluation by the transmitter generates a series of zeros
and ones, which is then encoded, sent through the 10-pin
dip switch, and finally sent by the antenna to the receiver
box. The transmitter and receiver set-up must both be at
the same frequency or the signal will not be received. The
frequency of the antennas must be the same, but the type of
antenna can be different.
The transmitter/encoder allows for the secure transmission
of up to 8 parallel binary outputs and has 3 10 address lines
for security. The signals from the footswitches are sent
to pins 7-10 on the transmitter/encoder, shown in Figure
48. If the FSR insoles were made wireless, the data would
be input into pin 2. When the pressure is applied to a
section of the footswitch, the input to the transmitter on
that line should show about 3V and nearly 0V if no pressure
is applied. As explained previously, the pull-down
resistor provides a very small voltage input (less than
0.001), which is determined to be a false signal by the
transmitter.
The Splatch antenna in the receiver box picks up the radio
frequency signal sent by the transmitter antenna, and then
sends the data to the 10-pin dip switch, which can only
receive data that came from a dip switch with the same pin
setting to reduce unwanted data from other radio frequency
devices operating at the same level. If the settings
match, the data is sent to the receiver/decoder, which was
also purchase from Linx Technologies and shown in Figure
52. The data is decoded and sent to the BNC-2120 by wires
that are soldered to the receiver outputs on pins 7, 8, 9,
and 12, shown in Figure 50. If the FSR insoles were made
wireless, the data would be output from pins 2 and 3.
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A
B
C
Figure 52: A)418MHz Splatch Antenna; B)10-Pin Dip Switch;
C)418MHz Transmitter/Encoder; D)418MHz Receiver/Decoder
National Instruments Equipment
The data acquisition devices used are the National
Instruments BNC-2120 and PXI-6040E, which is housed in the
PXI-1031, shown in Figures 53, 54, and 55, respectively.
The BNC-2120 is a shielded connector block that connects
the up to 8 analog and 8 digital inputs to the PXI-6040E.
The FSR input signals are connected to the BNC-2120 using
BNC connectors, which have a red lead that connects to the
wire that extends from the FSR driver circuit and the black
lead, is connected to ground. The footswitch output wires,
extending from the receiver box, are attached to the
digital inputs on the BNC-2120. The BNC-2120 sends the
data through a DAQ Card connector cable to the PXI-6040E.
The PXI-6040E is a data acquisition device that performs
high speed continuous data logging and supplies the data to
the computer to be received and displayed using the
LabVIEW® 8.1 program’s data acquisition assistant (DAQ
Assist) module, which creates, edits, and runs task that
allows manipulation and displays of the data received.
D
Page 60

Analog Inputs
Digital Inputs
Figure 53: National Instruments BNC-2120
Page 61

Figure 54: National Instruments PXI-6040E
Figure 55: National Instruments PXI-1031
Page 62

4. Trouble-Shooting
Problem Possible cause How to fix it
1.
After turning the switch
on, there is no voltage
going through
Dead batteries
Turn switch off,
replace batteries, and
turn it back on, if
still not working,
means that something
is damaged
2.
After changing the batteries,
still no voltage is going through
switch is damaged or battery wires are
disconnected
Replace the switch with a new one,
or resolder the battery wires
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3.
If no output is coming out of the
footswitches
LEMO connectors are damaged, or
wires are disconnected, or pull down
resistor are burned
Replace or fix the LEMO, or solder
new wires, or replace the resistors
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4-
If no output coming out of the FSR's
LEMO connectors are damaged, or
disconnected wires, or one of the Op
Amps is burned
Replace or fix the LEMO, or
solder new wires, or replace
the Op Amps
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5.
If the output voltage is negative voltage regulator is damage Replace the voltage regulator
6.
If the LabVIEW program is not
showing any readings
The output wires from the receiver box
are disconnected, or the PXI1031 box is
off
Reconnect the wires correctly
to the BNC2120 board, or turn
on the PXI1031 box
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7.
If the footswitches and the FSR's are
working but the transmitter is not
receiving any information
The transmitter is burned
Replace it with new
transmitter of the same
frequency
8.
If the receiver box is not getting any
information
The receiver itself is damaged
Replace the receiver with a
new one of the same
frequency
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9.
If you replaced the receiver but still
not getting anything
Either one of the antenna is damaged
Replace the Antenna with new
one of the same frequency
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10.
If LabVIEW program is not working
properly
The PXI1031 box was off after the
computer was on
Turn off the computer, start
the PXI1031 box first, than
turn back on the computer
11.
If everything inside the box are
working but you still can't get
anything out of the FSR's
The sensors inside the insoles are
damaged
Get new sensors and built
new insole following the steps
we mentioned earlier
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12.
If everything inside the box is
working but you still can’t get
anything out of the footswitches
The switches inside the insoles are
damaged
You can try to fix it but we
suggest that you replace the
whole thing
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13.
If the male LEMO connector is not
fitting into the female one
The pins of either one is bent
Try to bend it back to its
original place, and if not,
replace the connector
14.
If the circuit board is working
properly but the receiver not getting
the complete information
The address for the transmitter is most
likely not matching the receiver one
Adjust the address so its
exactly the same
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15.
LabVIEW program not receiving
information from four switches
wires are disconnected
Make sure that all the wires
are in the right place in the
BNC2120 board
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16.
If LabVIEW program still not working
The BNC2120 board is not connected
properly to the PXI1031 box
Reconnect the cable coming
between the BNC2120 board
and the PXI1031 box
17.
If LabVIEW program is giving
strange values for the time
Wrong format for values in Excel sheet
Make sure to convert the time
format from scientific notation
to number values
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Page 74

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18.
If the output is showing weird
numbers
The wires inside the box are crossing
over or touching different components
Relocate the wire so they
don’t get in contact with
anything else
19.
If the output of the FSR's is negative
the third Op Amp is damaged
Replace the Op Amp with new
one and make sure its in the
right direction
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20.
If the circuit is working fine but the
output of the FSR's is not what you
expected
Problem of connection
Check the wires coming out of
the insoles and resolder if
needed
Page 77