knee rehabilitation monitor

1

Knee Rehabilitation Monitor

Design Review

Project #11:

Mark Hernandez

Nicholas Pesce

Gurmehar Lugani

Samik Mody (MBA)

TA: Cara Yang

ECE 445, Senior Design, Spring 2015

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Table of Contents

1. Introduction ......................................................................................... 4

1.1 Statement of Purpose ..............................................................................................................4

1.2 Objectives ...............................................................................................................................4

1.2.1 Goals and Benefits ......................................................................................................4

1.2.1 Functions and Features ...............................................................................................4

2. Design .................................................................................................... 5

2.1 Block Diagrams ......................................................................................................................5

2.1.1 System Level Diagram ................................................................................................5

2.1.2 Software Diagrams......................................................................................................6

2.1.2.1 Device initialization and calibration ............................................................6

2.1.2.2 Everyday Mode ............................................................................................6

2.1.2.3 Inactivity Mode ............................................................................................7

2.1.2.3 Exercise Mode .............................................................................................8

2.1.2.3.1 Heel Slides ....................................................................................8

2.1.2.3.2 Straight Leg Raises .......................................................................9

2.2 Block Descriptions ...............................................................................................................10

2.2.1 Control Unit ..............................................................................................................10

2.2.2 Sensors ......................................................................................................................10

2.2.3 Power Source ............................................................................................................11

2.2.4 Feedback ...................................................................................................................11

3. Schematics .......................................................................................... 13

3.1 Microcontroller .....................................................................................................................13

3.2 Flex Sensor ...........................................................................................................................14

3.3 Accelerometer ......................................................................................................................16

3.4 Gyroscope .............................................................................................................................18

3.5 EMG .....................................................................................................................................20

3.6 Vibration Motors ..................................................................................................................24

3.7 Battery Management System ...............................................................................................26

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4. Calculations and Simulations ........................................................... 28

4.1 Flex Sensor ...........................................................................................................................28

4.2 EMG .....................................................................................................................................30

5. Requirements and Verification ........................................................ 35

5.1 Control Unit ..........................................................................................................................35

5.2 Sensors .................................................................................................................................37

5.3 Feedback ...............................................................................................................................41

5.4 Power Source ........................................................................................................................42

6. Tolerance Analysis ............................................................................ 44

7. Cost and Schedule ............................................................................. 46

7.1 Cost Analysis ........................................................................................................................46

7.1.1 Labor .........................................................................................................................46

7.1.2 Parts...........................................................................................................................46

7.1.3 Grand Total ...............................................................................................................46

7.2 Weekly Schedule ..................................................................................................................47

8. Ethics and Safety ............................................................................... 48

8.1 IEEE Code of Ethics ............................................................................................................48

8.2 Safety ....................................................................................................................................48

9. References .......................................................................................... 49

Appendix ................................................................................................ 50

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1. Introduction

1.1 Statement of Purpose

There are currently 100,000 ACL reconstruction knee surgeries and over 700,000 total

knee replacement surgeries annually in the United States.[1] Postoperative and preoperative

physical therapy are some of the most vital factors in recovering from these types of surgeries.

However, patients are at risk of re-injuring themselves at home when they are not under a

physical therapist’s supervision. Misguided home activity can potentially prolong the

rehabilitation period and add to the patient’s medical costs. We plan to develop a wearable knee

sleeve equipped with sensors that will aid the rehabilitation process by providing immediate

feedback to the user and allowing the physical therapist to monitor a patient’s knee health at

home. The feedback will allow patients to know if their actions at home are safe or if they are

performing their exercises correctly. The sensor data will let the physical therapists know if the

patients are following their prescribed home workout routine.

Many individuals have expressed interest in our project because they, or someone close

to them, have struggled with knee rehabilitation in the past. We believe that our idea can greatly

benefit those who will deal with this problem in the future – empowering them to rehabilitate

safely and effectively.

1.2 Objectives

1.2.1 Goals & Benefits:

● Accelerate the rehabilitation process for patients after knee surgery.

● Allow physical therapists to monitor a patient’s home activity and to enhance

supervised treatment.

● Provide user the feedback and the confidence to carry out home exercises.

● Reduce the chances of further injury.

1.2.2 Functions & Features:

● A wearable sleeve embedded with sensors that acquire information about a user’s

knee movements

● Different modes for knee movement analysis and feedback (everyday mode,

exercise mode, inactivity mode)

● Vibrational and visual feedback to immediately alert the user if an exercise is

being done properly or if there is an unhealthy knee movement being sensed

● Data storage for the user and physical therapist to track home activity using

additional software

● Carefully selected sensor placement and adaptive thresholds to address the

variations in knee structure among patients

● Compact all-in-one design for unobtrusive placement on knee

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2. Design

2.1 Block Diagrams

2.1.1 System Level Diagram

Figure 1: System Level diagram of the device

Figure 1 shows the high level overview of the device. The device has four major blocks:

Sensors, Control Unit, Power source and Feedback. The Sensors block include the following

modules: flex sensor for measuring joint angle, the accelerometer and gyroscope to measure the

orientation of the joint and jerk it experiences, the EMG to measure the activity of the muscle

being monitored, and the push button/joystick for receiving user feedback for the navigation

menu on the LCD. The Control unit block includes the following modules: Microcontroller that

controls the entire device, the Storage device that stores diagnostic data of joint that is being

monitored. The feedback unit consists of the LCD on which the navigation menu will be

displayed, and the vibration motor which will alert the user if using the joint in an injurious

manner. The Power Source block consists of a battery health monitor and gates for controlling

power to other blocks in the device.

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2.1.2 Software Diagrams

2.1.2.1 Device initialization and calibration

Figure 2: Initialization mode state diagram

The initialization mode for the device can either be prompted by the user or will be

automatically invoked if calibrations for the sensors are not found in the memory. Once the

device is in this mode, it will guide the user through the process of calibrating the sensors using

the LCD, push button and joystick. The calibrations will be saved in the memory and the device

will prompt the user to select the next mode.

2.1.2.2 Everyday mode

The everyday mode is activated when the device is wore on a regular day while walking

and sitting. There are joint movements that can re-injure a recovering patient and the knee

rehabilitation monitor can detect these movements and warn the user using the vibration motors.

The two movements that are potential harmful are knee twist and jerk. The diagrams below show

how twist and jerk are calculated.

Figure 3: Twist detection state diagram

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Figure 3 shows the state diagram from twist detection. The microcontroller detects the

twist of the knee by using a combination of gyroscopes on the knee and the ankle. If the change

in angle detected by the knee gyroscope with respect to the ankle gyroscope exceeds an

experimental threshold t, twist is detected and the user is warned by turning on the vibration

motors.

Figure 4: Jerk detection state diagram

Figure 4 shows the state diagram from jerk detection. The jerk is detected by the

accelerometer on the knee by measuring the derivative of acceleration on each of the axes. If the

derivative exceeds an experimental threshold t, jerk is detected and the user is warned by turning

on the vibration motors.

2.1.2.3 Inactivity Mode

This mode is responsible for detecting if the user has not moved the joint for a

programmable amount of time. Figure 5 shows the flex sensor reading is monitored and the user

is warned if the user has been in a position for prolonged period of time that can potentially harm

the joint.

Figure 5: Inactivity mode state diagram

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2.1.2.4 Exercise mode

In this user selectable mode, the twist and the jerk detection will be suspended and the

user will be executing the exercises prescribed by the physiotherapist. The knee brace will

provide encouragement when the user completes an exercise correctly. The following two

exercises will be present in the knee brace for monitoring.

2.1.2.4.1 Heel Slides

Figure 6: The proper execution of a heel slide exercise[7]

In this exercise the user lays down on his back on a hard surface. The heel is

slowly moved up towards the buttocks, as far as is comfortable. The knee monitor detects

if the user has been able to reach the angle it had before and encourage him with vibrating

the motors once. If the user goes beyond the previous angle captured, the new angle is saved and

the motors vibrate twice. Figure 6 shows the pictorial description of the exercise and Figure 7

shows the software state diagram used to detect the exercise and provide feedback.

Figure 7: State Diagram for the heel slide exercise

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2.1.2.4.2 Straight Leg Raises

Figure 8: The proper execution of a leg raise exercise[8]

In this exercise the user lays down on his back on a hard surface. While keeping

one leg bent at a 90 degree angle, the user will slowly lift the rehabilitating leg upwards,

keeping the knee joint as straight as possible. The user will stop when the two quadriceps

are in line, and then hold that position for a specified amount of seconds. The user will

finish by slowly bringing back the leg to the ground. This exercise helps in regaining

quadricep muscle strength that is lost after the surgery. The motions of this exercise can

be analyzed by the gyroscope. The flex sensor can also track if the user’s leg stays

straight. Figure 8 shows the pictorial representation of the leg raise exercise.

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2.2 Block Descriptions

2.2.2 Control Unit

The control unit is responsible for controlling all of the sensors, feedback devices, and

power source. It is also responsible for logging data from the sensors for post-processing and

analysis. battery maintenance purposes.

Microcontroller:

The microcontroller is responsible for controlling all the feedback devices in

the system as well as collecting and interpreting data from the sensors. It will also

control components of the power supply to manage the power consumption of the

device. It consists of the software that is capable of choosing modes of the device from

everyday mode, exercise mode or inactivity mode.

Data Storage:

The data storage will consist of a micro SD card with its associated circuitry to

interface it with the microcontroller via a serial communication. It is responsible for

saving data from the device for offline post processing.

2.2.2 Sensors

The sensor block contains devices that acquire real-time mechanical and physiological

information from the user’s knee. Additional circuitry for the sensors is implemented to allow

them to be interfaced with the microcontroller. Outputs from this block include critical sensory

data that describes the knee joint angle, knee motions, and quadricep muscle activity.

Flex Sensor:

The flex sensor is a thin strip, around 4.5 inches in length, that is used to monitor

the user’s knee joint angle. When the device is attached on the knee and bent, the flex

sensor circuitry will output unique output voltage which will describe the user’s range of

motion. Evaluation of the flex sensor data can help confirm that the user’s are reaching

their milestones in knee extension and knee flexion.

Accelerometer:

The accelerometer is a sensor positioned about 2 inches above the knee cap. It is

used to measure the acceleration that is being experienced by the leg along the x,y, and z

axes in space. The natural acceleration of gravity allows this sensor to give a

measurement of the leg’s orientation with respect to the ground. The accelerometer can

also give information about any abrupt changes in acceleration (jerk) that could be

dangerous for the user.

Gyroscope:

Two gyroscope sensors will be used in the design to measure the angular

acceleration of the upper and lower leg. One gyroscope is positioned about 2 inches

above the knee cap laying on the quadricep muscle. A second gyroscope chip is

positioned in the middle of the anterior side of the tibia (in front of the shin). The

combination of these sensors give information of unwanted lateral or medial movement

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of the knee joint such as twisting. Additionally, the gyroscope data can characterize the

motions of repetitious leg workouts, especially the heel slides and leg raises mentioned in

section 2.1.2.4.

Electromyograph (EMG):

The EMG is a sensor that is used to detect the electrical muscle activity of the

quadricep. Three electrodes are used: one on the kneecap, one on the lower quadricep,

and one on the upper quadricep. A series of analog filters and bio-instrumentation

amplifiers will condition the EMG signal to only include quadricep muscle contractions.

Push Button and Joystick:

The push button and joystick directly interfaces with the LCD panel. This allows

the user to navigate a menu of device settings displayed on the LCD. The user can select

their preferred mode as well as calibrate baseline sensor measurements for exercise. 2.2.3 Power Source

The power source block provides power to all of the components in the system. A battery

is used as the main power source, while the battery management system (BMS) regulates the

power being distributed. An additional battery management feature allows the user to know

when the battery is running low.

9 Volt Battery:

The 9 volt battery serves as the main power source in the device. It will provide

the battery management circuitry with the raw power to be conditioned and allocated to

different blocks of the system.

Battery Management System (BMS):

The battery management system is responsible for distributing the power

throughout the system. Three voltage regulators in the BMS steps the battery voltage

down to coincide with the power supply requirements of the different devices in the

system. Input from the microcontroller can disable certain regulators when a certain

block is not needed. The BMS will also have a built-in feature that alerts the user when

the battery is about to die via LEDs.

2.2.4 Feedback

The feedback block consists of the devices that will alert the user with important

information regarding their knee health. Depending on the mode, the feedback systems activate

when the sensor data indicates unhealthy knee movements or correct knee movements for

exercises.

Vibration Motor:

Two vibration motors in the knee sleeve (one in the front of the leg, and one in the

back) provide haptic feedback to the user. In instances of unhealthy knee movements, the

vibration motors serve to immediately get the user’s attention. Additionally, the two

vibration motors will be activated at different times during exercise to provide the spatial

cues.

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Liquid Crystal Display (LCD):

Once the vibration motors alerts the user initially, the LCD provides user with

more specific visual feedback. Messages are displayed on the LCD panel with the current

mode, suggestions, warnings, repetition counts, or positive feedback. It is also used to

debug the software during development of the prototype. The LCD interfaces with

microcontroller via 11 GPIOs. A Serial-in Parallel-out shift register would be used to

interface the LCD with microcontroller.

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3. Schematics

3.1 Microcontroller

Figure 9: Microcontroller schematic without neighbouring components

Microcontroller Schematic Description

Inputs: Regulated 3.3VDC +/- 1% from Power Source

SPI bus input

Analog voltage from flex sensor

Analog voltage from EMG circuitry

Outputs: Digital levels 0 (0V +/- 1%) and 1 (Vcc +/- 1%) for chip selects, shift regs

SPI Bus data, and clock

Figure 9 depicts the microcontroller connections. It consists of a status LED

connected to Vcc which shows if the microcontroller is receiving power. C1 is

responsible for reducing noise in the input voltage and C2 allows the controller to save

critical data into flash before losing power.

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3.2 Flex Sensor

Figure 10: This schematic shows the connection between the microcontroller and the Flex

Sensor. The flex sensor voltage is sensed through an on-board analog to digital converter.

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Flex Sensor Schematic Description

Inputs: Regulated 3.3 VDC +- 1% from Power Source

Outputs: Analog output voltage of the flex sensor circuit to Control Unit

The flex sensor acts as variable resistor which changes resistance when it is bent.

Higher angles of bending correspond to higher resistances. The circuit shown in Figure

10 allows an output voltage (related to the flex sensor resistance and bend angle) to be

interfaced with the microcontroller’s analog-to-digital converter. The flex sensor is

incorporated into a voltage divider circuit and put through an impedance buffer.

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3.3 Accelerometer

Figure 11: This schematic shows the connection between the microcontroller and the ADXL362

accelerometer. The accelerometer is connected via SPI and provides an interrupt facility that

can wake the controller up when activity is detected.

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Accelerometer Schematic Description

Inputs: Regulated 3.3 VDC +- 1% supply voltage from Power Source

SPI clock signal (SCLK) from Control Unit

SPI chip select bit (CS) from Control Unit

SPI master output, slave input signal (MOSI) from Control Unit

Outputs: SPI master input, slave output signal (MISO) to Control Unit

Interrupt signal (INT1) for activity detection to Control Unit

The digital 3-axis acceleration data from this sensor is interfaced with the

microcontroller’s SPI input pin for data analysis. Additionally, one of the interrupt bits

(INT1) is used to as a wake-up signal for the microcontroller. A built-in feature of the

accelerometer chip allows the activity detection; if leg movements are detected by the

accelerometer, the interrupt signal will take the microcontroller out of its low-power

mode, reactivating all of its normal functions and data storage.

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3.4 Gyroscope

Figure 12: This schematic shows the connection between the microcontroller and the ITG-3400

gyroscope chip. There are two chips connected to the micro, one for the ankle and one for the

knee. The chip select signal from the microcontroller will decide which chip will transmit data

over the SPI bus.

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Gyroscope Schematic Description

Inputs: Regulated 3.3 VDC +- 1% supply voltage from Power Source

SPI clock signal (SCLK) from Control Unit

SPI chip select bit (nCS) from Control Unit

Outputs: SPI Serial Data Output (SDO) to Control Unit

The digital 3-axis angular acceleration data from this sensor is interfaced with the

microcontroller’s SPI input pin for data analysis. Two gyroscope chips are used on the

upper and lower leg in order to quantify unhealthy twisting motions. This is done by

evaluating the differences in angular acceleration between the two sensors.

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3.5 EMG

Figure 13: The Bio-Instrumentation Amplifier internal circuitry model. All disconnected wires

are unused pins which are connected in the overall EMG circuit schematic but are left out here

for description purposes.

Input Voltage Drop across 2 Electrodes (V1-V2)

Output Vin*278 G = 278 V/V

The AD622 chip itself houses all of the circuitry seen in Figure 13 in a single IC. There

will be no physical diodes or resistors in this part of the circuit as these are included in the

AD622 package. It is important however to discuss the various components of this amplifier to

better understand its functionality. The diodes are all high power rating, pull down, laser cut

elements housed inside the AD622 chip to prevent voltage spikes from giving the user a shock.

This concept is more important during testing of this circuit element rather than in the

application of it due to the fact that the finished circuit will contain only DC power sources from

a low voltage battery minimizing the chance of a high voltage spike. The two resistors function

to limit the input current to be less than 60 mA which is the safe operating current of the AD622

package. Our design does not require monitoring of this input current as voltages originating at

the two input leads will be sufficiently small as to never exceed the required 60 mA. The

triangular box represents the pin-set of the AD622 chip and displays all 8 of the chip’s pins.

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Figure 14: Band Pass Filter

Input Vout from AD622 with G = 278 V/V

Output Vout = Vin * 10 G = 10 V/V

As seen in Figure 14, the LM741 operational amplifier serves to both amplify and filter

the input voltage signal seen at R3. The output and input of this section of the schematic are left

unconnected due to the fact that this picture represents a modular component of a larger EMG

circuit element where input and output voltages are not determined. In this picture of the Band

Pass Filter circuit element, 4 external components are required and used along with the LM741

chip which houses only an operational amplifier. The capacitances and resistances must be

carefully chosen to open a frequency window of which all frequencies outside will be negated.

These values set not only the voltage gain for this circuit element but also the frequencies

attenuated.

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Figure 15: High Pass Filter

Input Voltage from first LM741

Output Vout = Vin*10

Repeated in its use once more, the LM741 operational amplifier is used once again in a

high pass filter application to wipe DC components picked up from various levels of

amplification or processing. The bandpass filter does indeed account for DC value removal

through its lower end frequency cut-off of 20 Hz. However, some noise is still produced from

DC frequencies hovering below 4 Hz which are picked up from amplification. These values are

attenuated by this high pass filter. Not only does this filter remove the strong DC component

from the output signal, it also steps up the voltage again by -10 V/V. Because the output from

Figure 15 is amplified by -10 V/V, the gain from the second amplifier should be negative to

correct for positive voltage outputs. Stepping up the voltage by another 10 V/V finally places the

output reading in the range needed for subsequent labview filtering and testing; 0 to +2 volts.

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Figure 16: Overall EMG Schematic

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3.6 Vibration Motors

Figure 17: This schematic shows the connection between the microcontroller and the vibration

motors. A 74HC595 8 bit shift register IC is used to extend the number of digital pins available

on the micro. The vibration motors are activated by supplying current to the switching

transistors.

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Vibration Motor Schematic Description

Inputs: Regulated 3.3 VDC +/- 1% supply voltage from Power Source

Enable bit to activate vibration from Control Unit

Outputs: None

When the enable signal from the microcontroller output is high, the transistor is

activated and current is allowed to flow from gate to drain. This will activate the

vibration motor which is being driven by the power supply.

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3.7 Battery Management System

Battery Management System Schematic Description

Inputs: 9 volt battery voltage

Outputs: Regulated 3.3VDC +/- 1% voltage to Sensors

Regulated 3.3VDC +/- 1% voltage to Control Unit

Regulated 3.3VDC +/- 1% voltage to Feedback

Figure 18: The battery monitoring circuit

The circuit for the battery voltage monitoring is depicted in Figure 18. The Zener

diode is the most vital component in this circuit as it determines the cut-off voltage to

indicate that the battery is running low.[6] A Zener diode with a breakdown voltage of 6

VDC +/- 5% is used. When the battery voltage is above this breakdown voltage, the

Zener diode will conduct, activating the first transistor, and allowing the green LED to

light up. When the battery voltage falls below this breakdown voltage, the Zener diode

will not conduct, activating the second transistor, and allowing the red LED to light up.

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Figure 19: Example of a voltage regulator circuit

The voltage across the Zener diode stays within 6VDC +/- 5% as long as the breakdown

voltage is satisfied. This is used as the input voltage to the voltage regulator circuit. An example

of the voltage regulator circuit is depicted in Figure 19. The stepped-down 6VDC +/- 5% is used

rather than the 9 volt battery to satisfy the voltage regulator input voltage specifications. Three

voltage regulators will be connected to the Zener diode voltage terminal and output regulated

voltages of 3.3 VDC +/- 1% to the sensors, control unit, and feedback blocks.

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4.1 Flex Sensor

Calculations for Flex Sensor Circuit:

Given the schematic for the flex sensor in Figure 10, the output voltage for the entire circuit is

essentially modeled as a voltage divider in Equation 1.

Eq. 1:

The resistance of the flex sensor (R_flex) varies depending on the angle in which it is

being bent. The datasheet for this device (FS-L-0095-103-ST) indicates that when the sensor is

completely flat, the resistance should measure 10k Ohms with a tolerance of +- 30%. When bent

180 degrees, the resistance should double to 20k Ohms +- 30%.

The output voltage of the flex sensor circuit is the parameter that is passed to the

microcontroller. In order to maximize the range of this output voltage parameter, a value for the

second resistor (R1) was chosen to be 14K ohms. This value was determined in Matlab, using a

maximum finding function given different R1 values ranging from 10K Ohms to 20k Ohms

shown in Equation 2.

Eq. 2:

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Simulations for Flex Sensor Circuit:

Figure 20: Simulated flex sensor output voltage with different sensor resistances

The simulation in Figure 20 illustrates the voltage output response given an input voltage

of 3.3 VDC from the Power Source block, varying with different flex sensor resistances. Given

the 30% tolerance of the flex sensor resistance, the range in which we expect to see the output

voltage at angles 0-180 degrees is highlighted in green. The maximized voltage difference

between is calculated to be 0.5662 V when R2 = 14K ohms. Different knee joint angles will be

mapped to a unique output voltage threshold within this range to describe the user’s range of

motion.

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4.2 EMG

Figure 21: High level block diagram describing components of the EMG detection circuitry

AD622 Texas Instruments Bio-Instrumentation Amplifier: The bio-instrumentation

amplifier is an AD622 Texas Instruments model. Gain is set through the use of an

external resistor across pins 1-8 seen in Figure 21 and discussed more in subsequent

calculation sections of this review.

LM741 Texas Instruments Operational Amplifier Band Pass Filter: The LM741 is

the operation amplifier chosen for this component of the physical EMG circuit design.

This amplifier is used as part of an active filtering element which removes frequencies

outside of a desired band. Features of the LM741 include output and input overload

protection as well as oscillation damping which reduces noise from amplification.

LM741 Texas Instruments Operational Amplifier High Pass Filter: The third block

in the high level logic block diagram describes the highpass filter needed for removal of

DC components. These DC values caused an unwanted offset in the output data which

was noisy. Specifically, the DC components removed were anything below 5 Hz.

Calculations regarding this block of the diagram will be discussed in the EMG

Calculations section of this review.

Calculations for Bio-Instrumentation Amplifier:

Eq. 3:

50.5

1GR k

G

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Figure 22: Required Values of Gain Resistors

The chart in Figure 22 was taken from the datasheet for the AD622 Operational

Amplifier[12]. Gain is set by placing a resistance across pins 1-8 of the AD chip. The table

in Figure 22 displays different theoretical gain values as well as the actual values

empirically derived from setting a number of pre-determined resistances across pins 1-8.

For our application, a good starting gain is in the range of 200-500 volts. A gain greater

than these values will be amplified too much in subsequent steps of processing and will

result in output values greater than the desired 0 to +2V range. A good compromise is to

use a resistor with a value around 182 ohms in order to set the gain to be 278 V/V.

Calculations for Bandpass Filter:

Since frequencies outside of 20-300 Hz are undesired, the values of R1, R2, C1 and C2 were

specifically chosen. The gain needed to be 10 V/V in order to increase the order of magnitude of

the voltage gain from the AD622 amplifier by 1 order of 10. This conditions the voltage to be

stepped up one last time before being filtered with software. In the Figure 14, R1 corresponds to

R3, R2 corresponds to R4 and C1 and C2 correspond to C1 and C2 respectively.

Eq. 4:

2

1

RGain

R

Eq. 5:

1

1 1

1

2fc

R C

Eq. 6:

2

2 2

1

2fc

R C

R1 was chosen to be 1000 ohms

R2 was chosen to be 10 kohms

32

C1 was chosen to be approximately 7.95 uF

C2 was chosen to be approximately 53 nF

fc1 = 20.019 Hz

fc2 = 300.2923 Hz

Vout/Vin = -10 V/V

Calculations for High-Pass Filter:

Eq. 7:

2

1

RGain

R

Eq. 8: 1

2fc

RC

R corresponds to R5 = 33 kohm

R1 corresponds to R5 = 33 kohm

R2 corresponds to R6 = 330 kohm

C corresponds to C3 = 1 uF

fc = 4.822 Hz

The overall gain from this circuit is set in parts and works to increase the order of

magnitude of the signals received at the electrode leads. The gain from the bio-instrumentation

amplifier is about 200-500 V/V. The bandpass and highpass filters both have a gain of 10 V/V.

Thus in total, the signal is amplified by 20000 - 50000 V/V. This is ideal because the acquired

voltages are in micro or nanovolts.

10-9 * 20,000 = .0002 V

10-6 * 20,000 = .02 V

Simulation for EMG (Labview):

Figure 23: Labview Simulation Block Diagram for EMG

33

Figure 23.a: Raw signal from DAQ

Figure 23.b: Raw signal filtered with band stop filter

Figure 23.c: Frequency spectrum of band stop filtered signal

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Figure 23.d: Final output EMG signals for muscle contraction detection

The simulations for the EMG were acquired through a three electrode lead system connected to

the EMG detection circuitry through the AD622 Amplifier. The unfiltered signal in Figure 23.a

is the raw waveform acquired base voltage waveform. The filtered signal in Figure 23.b is the

waveform without 60 Hz noise. Figure 23.c displays the frequency domain of the 60 Hz filtered

waveform. Figure 23.d is depicts the final output voltage from the EMG circuit. This signal is

used fed into the microcontroller for further evaluation of the user’s muscle contraction patterns.

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5. Requirements and Verification

5.1 Control Unit

Requirements Verification Points

Microcontroller 20

a. The microcontroller is able to

program flash memory when

input voltage to the

microcontroller is 3.3V +- 5%

b. The microcontroller is able to

communicate over the Serial

Bus.

a.

● Attach the microcontroller input

supply to a power supply capable of

producing voltage of 3.3V.

● Attach the USB to the computer and

open Code Composer[10] software

provided by Texas Instruments

● Program the controller with the code

mentioned in Appendix C1

● Verify that the onboard LED toggles

every 1 sec.

b.






provided by Texas Instruments and

flash the controller with the code

provided in Appendix C2

● Open the Serial port emulation

software Tera Term[11]

● Send a string of at least 10 characters

using the Serial monitor in the

software and verify that the controller

is sending back the same string on the

serial monitor

● Repeat this test 10 times by sending

strings with different lengths and

characters. Verify the sent data is the

same as what is received from the

microcontroller

36

c. The microcontroller is able to

sense voltages via the analog

pins using the onboard ADC

within ranges of 0.0V - 3.3V

+/-5% with a precision of

3mV +/- 1%

d. Microcontroller can produce a

digital low of less than 0.7V

and a digital high of greater

than 1.3V

c.




● Attach a function generator to the pin

P1.1 on the microcontroller






● Open the Serial port emulation

software Tera Term[11]

● Increase the voltage on the function

generator from 0.0V to 3.3V at

3.3mV increments

● Verify that the value broadcasted on

the serial monitor goes from 0 (for

0.0V) to 1023 (for 3.3V) linearly i.e.

for every 3.3mV increment, the value

on the serial monitor increases by 1.

d.




● Attach a multimeter to the pin P1.1 on

the microcontroller






● Verify that the multimeter reads a low

voltage of less than 0.7V and a high

voltage of greater than 1.3V and the

low and the high is toggled every one

second. .

Data Storage 5

a. The data storage should be

able to Connect the Micro SD

to the SPI Bus. Use the

a. Remove the SD card from the device

and hook it up to a computer to check if

the file sizes are exactly what were

37

available SPI library to write a

file with size ranging from

1KiB to 1MiB with all zeros.

written and data was all zeros.

5.2 Sensors


Flex Sensor 10

a. The absolute maximum

ratings for the

microcontroller’s input pin

voltage is -0.3 VDC to Vcc +

0.3 VDC (Vcc = 3.3V +/-

1%). The flex sensor circuit

output must be:

-0.3V < vout,flex < 3.6 V

b. The microcontroller ADC

input resolution is

approximately 3 mV +/- 1%.

The flex sensor circuit output

voltage must change by a

minimum of 3 mV +/- 1%

when the angle of the flex

sensor is changed 10° in any

direction between 0° and 130°

|Δvout,flex| > 3 mV.

a.

● Assemble the complete flex sensor

circuit described in Figure 10 of

section 2.2.2 on a breadboard.

● Use multimeter to probe the voltage

between the output of the impedance

buffer (vout,flex) and ground.

● Bend the flex sensor from 0° to 180°

(pinch bend) and observe the output

voltage on the multimeter.

● Verify that the output voltage stays

within the maximum ratings of the

microcontroller.

b.

● Assemble the complete flex sensor

circuit described in Figure 10 of

section 2.2.2 on a breadboard.


between the output of the impedance

buffer (vout,flex) and ground.

● Rest the flex sensor along the two

axes of a flat goniometer.

● Adjust the angle of the goniometer

and flex sensor by increments of 10°

● Record the observed voltage on the

multimeter, from 0° to 130°.

● Verify that the change in voltage |Δv|

exceeds 3 mV between every adjacent

datapoint.

38

Accelerometer 10

a. Supply voltage must be

between 1.8 VDC and 3.5

VDC.

b. The accelerometer must sense

an acceleration of 1g +/- 10%

on a single axis when

completely flat.

a.

● Attach the accelerometer input supply

to a DC power supply.

● Sweep the voltages from 1.0 VDC to

4.0 VDC

● Verify that the device is active within

the specified range.

b.

● Connect SPI output of the

accelerometer to microcontroller.

● Place sensor completely flat along

one axis.

● Verify that the microcontroller

indicates high values on one side (+1g

+/- 10% or 768 on the

microcontroller) and values close to

zero for the other sides (0g +/- 0.1g or

512 on the microcontroller).

● Rotate the sensor about a single axis.

● Verify that the values of one axis

increase and another axis decrease.

Gyroscope 10

a. Supply voltage must be

between 1.8 and 3.3VDC +/-

5%.

b. Gyroscope SPI output must

measure above 0g +/- 0.1g

when allowed to freefall.

a.

● Attach the gyroscope input supply to

a DC power supply.

● Sweep the voltages from 1.0VDC to

4.0VDC

● Verify that the device is active within

the specified range.

b.

● Connect SPI output of the gyroscope

to microcontroller.

● Attach gyroscope to a side of a

goniometer.

● Hold the goniometer at a 180° angle.

● Release the side with the sensor and

allow it to swing like a pendulum.

● Observe the sensor values through the

microcontroller and verify that the

angular acceleration of the

39

appropriate axis exceeds the given 0g

+/- 0.1g value during the initial free

fall.

EMG 15

a. Bio-instrumentation amplifier

must have an accurate gain

setting through a resistor

pinned between pins 1 and 8

of the AD622 Chip +/- 0.15%.

The AD622 is built to run on

6 mA of current at a

maximum over long

durations. Thus input voltages

must be limited to be less or

equal to a microvolt.

b. Bandpass filter gain must be

within 10V/V +/- 10%

c. Bandpass filter corner

frequencies of fc1 and fc2 must

be 20Hz +/- 10% and 300Hz

+/- 10% respectively

a.

● Place a resistor from the chart found

under section 2.2.6 and connect a

small test voltage (1 mV).

● Measure the output voltage of the

AD622 using a multimeter and record

the voltage.

● Calculate gain (Vout/Vin).

● Reference the chart found in Figure

22.

● Verify that the measured gain

matches theoretical values with a

tolerance of +/- 0.15 %. b. In order to verify that the bandpass filter

element is operating as intended, the

resistors and capacitors must be within a

tolerance of +/- 5% of the values listed

on the block diagram of this report. This

is to hold the gain at a constant and

predictable value.

● Hook up the circuit as described in

Block 2 and match resistor and

capacitor values.

● Measure the output voltage from the

bandpass filter circuit by supplying a

test voltage of 1 V.

● Measure Vout/Vin to calculate the

gain.

● The gain must be 10 V/V +/- 10% to

be predictable.

c. If the gain is within an acceptable range,

then the cutoff frequencies will be as

well.

● Calculate the cutoff frequencies using

the equations listed under the Block 2

Description section above

● Verify that the calculated high and

low cutoff frequencies are +/- 10 % of

40

d. High pass filter gain must be

within 10V/V +/- 10%

e. High pass filter cutoff

frequency fc = 4-5Hz

the desired 20-300 Hz band.

d. In order to verify that the high pass filter

element is operating as intended, the

resistors and capacitors must be within a

tolerance of +/- 5% of the values listed

on the block diagram of this report. This

is to hold the gain at a constant and

predictable value.

● Hook up the circuit as described in

Block 3 and match resistor and

capacitor values.

● Measure the output voltage by

supplying a test voltage of 1 V.

● Measure Vout/Vin to calculate the

gain.

● The gain must be 10 V/V +/- 10% to

be predictable.

e. If the gain is within an acceptable range,

then the cutoff frequencies will be as

well.

● Calculate the cutoff frequency using

the equations listed under the Block 3

Description section above

● Verify that the calculated frequency is

inside of the required 4-5 Hz range.

Joy Stick and Push Button 5

a. Connect the two

potentiometer in a voltage

divider circuit and sense the

drop across them.

b. Pull the microcontroller pin

where the push button is

connected to high. Connect

the other terminal of the push

button to ground with a 10k

ohm resistor in series.

a. Check if drop at full extension in both

negative and positive direction is 1.5V

+- 5% and at center position is 1.0V +-

5%

b. When the push button is pressed the

microcontroller should sense a drain to

ground on the pin the push button is

connected to. The pin should be pulled

to high again when the button is

depressed.

41

5.3 Feedback


Vibration Motors 5

a. Start voltage of 2.3 VDC, and

voltage range within 2.5 VDC

and 3.8 VDC.

a.

● Connect the vibration motor in series

to a DC power supply.


across the vibration motor terminals.

● Sweep the voltages from 2.0 VDC to

4.5 VDC.

● Verify that the vibration motor

activates when the voltage exceeds

2.3 VDC +- 1%.

● Verify that the device is vibrating

within the appropriate voltage range

(2.5 - 3.8 VDC).

Liquid Crystal Display (LCD) 5

a. Connect the LCD data pins to

the microcontroller digital

pins. Run the software to

exercise each segment on the

LCD

a. Inspect visually if all segments light up

one by one.

42

5.4 Power Source


9 Volt Battery 5

a. The input to the battery health

monitoring circuit must be

above 6 VDC +/- 5%. The

battery must output a voltage

above this threshold.

a.


across the positive and negative

terminals of the 9 volt battery.

● Verify that the measured voltage is

above the given threshold for the

battery health monitoring circuit.

Battery Management System 10

a. The voltage regulators have a

maximum input voltage rating

of 7 VDC. The voltage across

the 6V Zener diode must be

below 7 VDC.

vzener < 7 VDC

b. Vibration motor start voltage

is 2.3 VDC. The input voltage

range for the vibration motor

is 2.5VDC ~ 3.8VDC. The

voltage regulator output

voltage must be within these

constraints:

vout,reg > vstart = 2.3VDC

2.5 V < vout,reg < 3.8 V

a.

● Connect the negative terminal of the

diode to the V+ terminal of a DC

power supply.

● Connect the positive terminal of the

diode to the V- terminal of the DC

power supply.


across the negative and positive

terminals of the Zener diode.

● Sweep the DC power supply voltage

from 6 VDC to 12 VDC.

● Verify that the voltage drop across the

Zener diode does not exceed 7 VDC

b.

● Connect voltage regulator input

voltage to V+ terminal of DC power

supply, and the GND pin to V-

terminal of DC power supply.

● Sweep DC power supply voltage


● Probe voltage regulator output with

multimeter.

● Verify that the output voltage is

greater than 2.3 VDC and within the

given input voltage range for the

vibration motors.

43

c. The microcontroller power

supply input pin operates at

voltage from 1.8 VDC to 3.5

VDC. The voltage regulator

must produce a voltage within

these constraints:

1.8 V < vout,reg < 3.5 V

d. The green LED must be on

and the red LED must be off

when the battery is above 6

VDC +/- 5%. The green LED

must be off and the red LED

must be on when the battery is

below 6 VDC +/- 5%.

c.

● Connect voltage regulator input

voltage to V+ terminal of DC power

supply, and the GND pin to V-

terminal of DC power supply.

● Sweep DC power supply voltage


● Probe voltage regulator output with

multimeter.

● Verify that the output voltage is

within the appropriate power supply

voltage range for the microcontroller.

d.

● Assemble the battery health

monitoring circuit described in Figure

18 on a breadboard, replacing the 9

Volt battery input with a DC power

supply input.

● Sweep the DC power supply voltage


● Verify that the LEDs are activated

and deactivated when the input

voltage transitions across the

threshold voltage.

44

6. Tolerance Analysis

One of the most important components of the device is the flex sensor. It gives

information of the user’s knee joint angle: a physiological marker that must be monitored closely

especially early on in rehabilitation. The datasheet for the flex sensor, however, does indicate

that it has a very large tolerance for its resistance when it is flat (+/- 30%). The plots in Figure 24

and Figure 25 illustrate how the flex sensor output voltage range changes with resistance values

at the extremes of their tolerance -30% and +30%.

Figure 24: The flex sensor response at a -30% of its resistance

Figure 25: The flex sensor response at a +30% of its resistance

45

The output voltage range for the -30% and +30% tolerance came out to be 0.55 V and

0.56 V, respectively. The original simulation in Figure 20 with 0% tolerance measured an output

voltage range of 0.5662 V. Even despite this large tolerance range in the flex sensor resistance,

the important output voltage parameter does not change significantly. The output voltage range

for both extreme cases are still well within the resolution requirements of the microcontroller

ADC (3 mV). With this being said, the device does not require a flex sensor with a tighter

tolerance than +/- 30%.

46

7.0 Cost and Schedule

7.1 Cost analysis

7.1.1 Labor

Name Hourly

Rate

Total

Hours

Invested

Total = Hourly Rate

x 2.5 x Total Hours

Invested

Mark $30.00 225 $16,875

Nick $30.00 225 $16,875

Gurmehar $30.00 225 $16,875

Total 675 $50,525

7.1.2 Parts

Item Quantity Unit Cost Cost

Microcontroller MSP-EXP430G2 1 $13.74 $13.74

Flex Sensors SEN-10264 2 $12.95 $25.90

Gyroscope Accelerometer MPU 6500 1 $22.95 $22.95

Gyroscope ITG-3400 1 $19.99 $19.99

Electrodes 3 $1.95 $5.85

Vibrational Motors ROB-08449 2 $4.95 $9.90

Push Button & Joystick 1 $5.95 $5.95

LCD Panel: Basic 16x2 Character LCD -

Black on Green 3V 1 $13.95 $13.95

3.3 V Regulator LD1117V33 5 $0.99 $4.95

9 Volt Battery & Holder DUR-PC16049V 1 $2.95 $2.95

Shift Register IC Shift Register 8-Bit –

74HC595 4 $0.63 $2.52

Micro SD-Card 1 $20.00 $20.00

Additional Logic Circuitry 1 $5.00 $5.00

Flexible Knee Brace 1 $15.00 $15.00

Total $168.65

7.1.3 Grand Total

Section Total

Labor $50,525.00

Parts $168.65

Grand Total $50,693.65

47

7.2 Schedule

Week Task Responsibility

9-Feb

Finalize proposal Mark

Prepare mock design review Nick

Research and select microcontroller Gurmehar

16-Feb

Design review sign-up Mark

Finalize Mock Review Nick

Research and select sensors Gurmehar

23-Feb

Purchase sensors and run tests Mark

Purchase microcontroller and run tests Nick

Writing software for tests Gurmehar

2-March

Test power source and interface with sensors and feedback Mark

Discuss initial PCB design Nick

Program microcontroller with initial bring-up Gurmehar

9-March

Assemble the prototype circuit on a breadboard Mark

Finalize design for PCB Nick

Write state machines for different modes in the device Gurmehar

16-March

Test the prototype circuit on the breadboard Mark

Order PCB Nick

Verify and test state machines for different modes in the device Gurmehar

30-March

Finalize the initial progress report Mark

Prepare the mock demo Nick

Solder parts onto the final PCB Gurmehar

6-April

Run tests on output of microcontroller Mark

Finalize mock demonstration Nick

Embedded the device into a knee sleve Gurmehar

13-April

Ensure functionality and Demonstration sign-up Mark

Run tests on final project Nick

Finalize any software changes Gurmehar

20-April

Write a MATLAB script for post-processing Mark

Finalize demonstration Nick

Presentation sign-up Gurmehar

26-April

Finalize presentation Mark

Discuss initial draft of final paper Nick

Lab checkout Gurmehar

3-May

Field test the device Mark

Finalize final paper Nick

Future propositions for the device Gurmehar

48

8. Ethics and Safety

8.1 IEEE Code of Ethics

In order for our product to be professional, there are specific IEEE codes of Ethics that

we must consider:

1. to accept responsibility in making decisions consistent with the safety, health, and

welfare of the public, and to disclose promptly factors that might endanger the public or

the environment;

This point is particularly important to us because of the liability issues that come with a

health-related product. Since we are dealing with individuals who are already treating fragile

injuries, it is imperative that we thoroughly inform the users how to properly operate the device.

Improper use of the device due to poor documentation can increase the risk of the user’s further

injuring themselves.

3. to be honest and realistic in stating claims or estimates based on available data;

If we make false claims on what our product can evaluate (or how well they can evaluate)

a patient’s rehabilitation process, it could lead to improper medical treatment and incorrect

feedback. It is our responsibility to thoroughly test our product and ensure that claims are backed

up by definitive data.

7. to seek, accept, and offer honest criticism of technical work, to acknowledge and correct

errors, and to credit properly the contributions of others;

We have already started consulting with multiple physical therapists and businesspersons

to evaluate our design. Many changes were made to the initial proposal based on the feedback

from these individuals. We must honor their contributions of these collaborators, we will

acknowledge their efforts, either monetarily or in the final reports and documentation.

8.2 Safety

The ultimate goal of the knee rehabilitation monitor is to ensure the safety of patients as

they recover from knee surgeries. With that being said, we want to eliminate any additional

health hazards that the device may pose to the user. One obvious concern is the fact that the

system is in such close proximity to the patient’s skin. In order to avoid any possibilities of an

electrical shock, we plan to isolate the electrical components in insulated casings to ensure that

they are not directly in contact with the patient.

However, there is one component in our device that requires direct contact with the

patients skin: the electrodes. In this case, precautions will be taken while developing the EMG

circuitry. The protection circuit for the bio-instrumentation amp consists of diodes and capacitors

that give a safe path to ground if any spikes of voltage are introduced both the patient and the

circuit will be safe.

49

9. References

[1] Incidence of anterior cruciate ligament injury and other knee ligament injuries: A

national population-based study, Gianotti, Simon M. et al. Journal of Science and

Medicine in Sport , Volume 12 , Issue 6 , 622 - 627 February 25th 2015

[2] Datasheet for microcontroller: http://www.ti.com/lit/ds/symlink/msp430g2313.pdf

February 25th 2015

[3] Datasheet for flex sensor:

https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/FLEX%20SENSOR%20DATA%20S

HEET%202014.pdf February 25th 2015

[4] Datasheet for accelerometer: http://www.analog.com/media/en/technical-

documentation/data-sheets/ADXL362.pdf February 25th 2015

[5] Datasheet for gyroscope: http://www.invensense.com/mems/gyro/documents/PS-ITG-

3400A-00.pdf February 25th 2015

[6] Datasheet for vibration motor: https://www.sparkfun.com/datasheets/Robotics/310-

101_datasheet.pdf February 25th 2015

[7] Battery management circuit: http://www.electroschematics.com/6338/battery-level-

monitor/ February 25th 2015

[8] Heel slide workout: http://www.borgess.com/default.aspx?pId=2150 February 25th 2015

[9] Leg raise workout: http://cari-brokenknee.blogspot.com/2012/03/straight-leg-raise-

challenge.html February 25th 2015

[10] Code Composer Studio: http://www.ti.com/tool/ccstudio February 25th 2015

[11] Tera Term http://en.sourceforge.jp/projects/ttssh2/releases/ February 25th 2015

[12] Datasheet for EMG operational amplifiers: http://www.analog.com/media/en/technical-

documentation/data-sheets/AD622.pdf February 25th 2015

http://www.ti.com/lit/ds/symlink/msp430g2313.pdf

https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/FLEX%20SENSOR%20DATA%20SHEET%202014.pdf

https://cdn.sparkfun.com/datasheets/Sensors/ForceFlex/FLEX%20SENSOR%20DATA%20SHEET%202014.pdf

http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL362.pdf

http://www.analog.com/media/en/technical-documentation/data-sheets/ADXL362.pdf

http://www.invensense.com/mems/gyro/documents/PS-ITG-3400A-00.pdf

http://www.invensense.com/mems/gyro/documents/PS-ITG-3400A-00.pdf

https://www.sparkfun.com/datasheets/Robotics/310-101_datasheet.pdf

https://www.sparkfun.com/datasheets/Robotics/310-101_datasheet.pdf

http://www.electroschematics.com/6338/battery-level-monitor/

http://www.electroschematics.com/6338/battery-level-monitor/

http://www.borgess.com/default.aspx?pId=2150

http://cari-brokenknee.blogspot.com/2012/03/straight-leg-raise-challenge.html

http://cari-brokenknee.blogspot.com/2012/03/straight-leg-raise-challenge.html

50

Appendix

#include <msp430g2553.h> // Initialize variables. This will keep count of how many cycles between LED toggles unsigned int i = 0; void main(void) { // Stop watchdog timer, // turns off the watchdog timer, which can reset the device after a // certain period of time. WDTCTL = WDTPW + WDTHOLD; // P1DIR configures the direction (DIR) of a port pin as an output or an input. P1DIR |= 0x01; // main loop for (;;) { // Toggle P1.0 using exclusive-OR operation (^=) P1OUT ^= 0x01; // Delay between LED toggles. for(i=0; i< 20000; i++); } }

Appendix C1: Code to toggle the on-baord LED of the micrcontroller

#include <msp430g2553.h> void main (void) { WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer CCTL0 = OUT; // TXD Idle as Mark TACTL = TASSEL_1 + MC_2; // ACLK, continuous mode P1SEL = TXD + RXD; P1DIR = TXD; // Mainloop for (;;) { RX_Ready(); // UART ready to RX one Byte _BIS_SR(LPM3_bits + GIE); // Enter LPM3 w/ interr until char RXed TX_Byte(); // TX Back RXed Byte Received } } // Function Transmits Character from RXTXData Buffer void TX_Byte (void) { BitCnt = 0xA; // Load Bit counter, 8data + ST/SP while (CCR0 != TAR) // Prevent async capture

51

CCR0 = TAR; // Current state of TA counter CCR0 += Bitime; // Some time till first bit RXTXData |= 0x100; // Add mark stop bit to RXTXData RXTXData = RXTXData << 1; // Add space start bit CCTL0 = CCIS0 + OUTMOD0 + CCIE; // TXD = mark = idle while ( CCTL0 & CCIE ); // Wait for TX completion } // Function Readies UART to Receive Character into RXTXData Buffer void RX_Ready (void) { BitCnt = 0x8; // Load Bit counter CCTL0 = SCS + OUTMOD0 + CM1 + CAP + CCIE; // Sync, Neg Edge, Cap } // Timer A0 interrupt service routine #pragma vector=TIMER0_A0_VECTOR __interrupt void Timer_A (void) { CCR0 += Bitime; // Add Offset to CCR0 // TX if (CCTL0 & CCIS0) // TX on CCI0B? { if ( BitCnt == 0) CCTL0 &= ~ CCIE; // All bits TXed, disable interrupt else { CCTL0 |= OUTMOD2; // TX Space if (RXTXData & 0x01) CCTL0 &= ~ OUTMOD2; // TX Mark RXTXData = RXTXData >> 1; BitCnt --; } } // RX else { if( CCTL0 & CAP ) // Capture mode = start bit edge { CCTL0 &= ~ CAP; // Switch from capture to compare mode CCR0 += Bitime_5; } else { RXTXData = RXTXData >> 1; if (CCTL0 & SCCI) // Get bit waiting in receive latch RXTXData |= 0x80; BitCnt --; // All bits RXed? if ( BitCnt == 0) { CCTL0 &= ~ CCIE; // All bits RXed, disable interrupt _BIC_SR_IRQ(LPM3_bits); // Clear LPM3 bits from 0(SR) } } } }

Appendix C2: Code to echo back the received Serial Data

52

include "msp430g2553.h" void main(void) { WDTCTL = WDTPW + WDTHOLD; // Stop WDT ADC10CTL0 = ADC10SHT_2 + ADC10ON + ADC10IE; // ADC10ON, interrupt enabled ADC10CTL1 = INCH_1; // input A1 ADC10AE0 |= 0x02; // PA.1 ADC option select P2DIR |= 0x01; // Set P2.0 to output direction WDTCTL = WDTPW + WDTHOLD; // Stop watchdog timer CCTL0 = OUT; // TXD Idle as Mark TACTL = TASSEL_1 + MC_2; // ACLK, continuous mode P1SEL = TXD + RXD; P1DIR = TXD; for (;;) { ADC10CTL0 |= ENC + ADC10SC; // Sampling and conversion start __bis_SR_register(CPUOFF + GIE); // LPM0, ADC10_ISR will force exit TX_Byte(); // TX the ADC10 } } // ADC10 interrupt service routine #pragma vector=ADC10_VECTOR __interrupt void ADC10_ISR(void) { __bic_SR_register_on_exit(CPUOFF); // Clear CPUOFF bit from 0(SR) } // Function Transmits Character from RXTXData Buffer void TX_Byte (void) { BitCnt = 0xA; // Load Bit counter, 8data + ST/SP while (CCR0 != TAR) // Prevent async capture CCR0 = TAR; // Current state of TA counter CCR0 += Bitime; // Some time till first bit ADC10MEM |= 0x100; // Add mark stop bit to RXTXData ADC10MEM = ADC10MEM << 1; // Add space start bit CCTL0 = CCIS0 + OUTMOD0 + CCIE; // TXD = mark = idle while ( CCTL0 & CCIE ); // Wait for TX completion } // Timer A0 interrupt service routine #pragma vector=TIMER0_A0_VECTOR __interrupt void Timer_A (void) { CCR0 += Bitime; // Add Offset to CCR0 // TX if (CCTL0 & CCIS0) // TX on CCI0B? { if ( BitCnt == 0)

53

CCTL0 &= ~ CCIE; // All bits TXed, disable interrupt else { CCTL0 |= OUTMOD2; // TX Space if (ADC10MEM & 0x01) CCTL0 &= ~ OUTMOD2; // TX Mark ADC10MEM = ADC10MEM >> 1; BitCnt --; } } }

Appendix C3: Code to broadcast ADC reading onto the serial monitor

knee rehabilitation monitor

Documents