Group 27SenseWalk
•
Mark Applegate
(EE)
•Sara
Belichki
(CpE)
•Matthew
Czarniak
(CpE)
•Nicholas
(EE)
Heintze


Improve the independence and quality of
life for the visually impaired.
Optimize a tool commonly used by the
visually impaired.

Sonar: detect upcoming obstacles and
vibrate a motor attached at the user’s
white cane.

GPS: the SenseWalk will hold the user’s
saved routes to guide them when needed.

Audio: the user will be alerted of
upcoming instructions as they go about a
route.
MCU
Audio
GPS
Digital
Compass
Power
Supply
SD
Card
Sonar
MCU
Audio
GPS
Digital
Compass
Power
Supply
SD
Card
Sonar

The SenseWalk requires a microcontroller
that contains
 High flash memory-between 256 KB-512 KB
 High frequency
 SPI connection
 Enough GPIO pins for the needed peripherals
 Low power
ATmega2560
Voltage Supply
5V
Frequency
16 MHz
Flash Memory
256 KB
GPIO pins
86
Supports SPI
Yes
IDE
Arduino IDE
Price with target $58.95
board
MCU
Audio
GPS
Digital
Compass
Power
Supply
SD
Card
Sonar
•
•
•
•
•
Distance From 1 meter to 3 meters
Sonar operate at 40kHz
Not affected by noise
Microcontroller calculate distance
Vibrate a motor at different magnitudes
proportional to distance
Ultrasonic Transducer
Selection
Senscomp 600
Air Ultrasonic
400ST/R
Thickness
0.46”
0.472”
Diameter
1.69”
0.63”
Frequency
50kHz
40kHz
Voltage
200V
20V
Operating
Temperature
-40 to +85o C
-40 to +80o C
Beam Angle
15 o at -6dB
55 o at -6dB
Capacitance
400-500pF
2400pF
Receiving
Sensitivity
-42dB at 50kHz
-65dB at 40kHz
Bandwidth Filter
Unknown
-6dB per 2 kHz
555 Timer
 Square wave is highly distorted by load.
Phase shift Oscillator
 Square wave is distorted by load.
40kHz Crystal- CMOS Inverter Oscillator
 Minimum distortion
Hex Inverter
Quad Op Amp
Sonar: Second MCU is needed to do the
calculations
 Sonar: High side switching needed to get rid of
noise
 Sonar: More gain is needed to pick up objects at
a further distance






Parallax Ultrasonic Distance Sensor
Interfaces directly with MCU
Libraries available to calculate distance
via MCU
Provides ADC conversion of sonar
readings onboard the sensor
Works from 2 cm to 3 m range
MCU
Audio
Digital
Compass
GPS
Power
Supply
SD
Card
Sonar



Needs an audio decoder to decode MP3
files into digital audio data
Be able to relay audio data to a
headphone jack
Be able to play certain tracks in realtime
depending on current GPS status that is
being relayed to the microcontroller

VS1053B audio decoder to decode MP3
files via input bitstream through SPI

Stores MP3 files on a microSD card
MCU determines when to play a track
from audio module
Audio sent out to headphone jack


MCU
Audio
GPS
Digital
Compass
Power
Supply
SD
Card
Sonar
ls20031
5 Hz update (10 Hz max)
Up to 66 channel input
Cold Start < 35 seconds
Accuracy to 3 meters
LSM303
I2C serial interface
Operating voltage: 2.5 to 5.5 V
Supply current: 10 mA



San Disk 4 GB
Petite FatFS
Stores Waypoints & MP3 Tracks


Use route planner to create CSV / GPX
Upload CSV file with waypoints to SD

Distance Calculation: (Haversine)

Angle to Waypoint Calculation:
Used current heading and angle to waypoint to
determine how to orient user
 Normalized the distance from the current heading
to the new heading in the clockwise direction,
counter clockwise direction, and also subtract the
current heading from the final heading.
 Pick the smallest of the three to be the correct
difference.

SenseWalk
SDCard
Compass
Bluetooth
Sonar
GPS
Init()
getDirection()
getCurrentCoordinates()
getCurrentWaypoint()
sendBluetooth()
calculateSonar()
determineRelativePos()
determineCorrection()
SDCard
OpenFile()
CloseFile()
ParseWaypoints()
CurrentWaypoint()
Compass
calibrateCompass()
currentDirection()
GPS
establishConnection()
currentCoordinates()
Audio
PlayTrack()
Sonar
determineDistance()
sendMotorCommand()
MCU
Audio
GPS
Digital
Compass
Power
Supply
SD
Card
Sonar

Energy Star Requirements have become industry standard
“AC-DC External Power Supply- An external AC-DC power supply is
an EPS designed to convert line voltage ac input into lower voltage dc
output.” [1]
Output Power:
14.4W
Minimum Efficiency Requirement: 73%
[1]
http://www.energystar.gov/ia/partners/prod_dev
elopment/revisions/downloads/FinalSpecV2.pdf
Flyback Switching Converter
High Efficiency 80+ % capable.
Least costly of all isolated switching power supplies.
Full isolation capable.
Ideal for 0-200Watts.
Limited to 200Watts due to high peak switch currents.
Magnetic & Capacitive
Component Issues
EMI design issues
Controller & FET
selection
CCM
DCM
CCM




Lower ripple current
Lower transistor and diode peak
current requirements
Right Half Plane Zero requires
complicated control loop
Higher energy in transformer =
larger transformer
DCM




Lower energy in transformer =
smaller transformer
Less windings = lower I2R Losses
Higher ripple current = output
capacitor ESR requirements
Higher transistor and diode peak
current requirements








Primary Inductance: 1.078mH
Primary Peak Current: 0.75A
Max Input RMS Current: 0.32A
Max Output RMS Current: 2.08A
Turn Ratio: 8.94
Primary & Secondary Wire Size
Core Material Selection
Gap Length, Total Winding Area


Power MOSFET required - 600V and >2 Amps.
Experiment with MOSFETs to find best fit for
efficiency.

Switching losses - Low parasitic capacitances
and fast rise/fall times will combat switching
losses.

Conduction losses - Low Rds(on) will combat
conduction losses.
MTP2N60E (ON Semi)
NDF03N60ZG (ON Semi) NDF06N62ZG (ON Semi)
VDSS
600V
600V
620V
ID
2A
3A
3.8A
Ciss
435pF
312pF
923pF
Coss
9.2pF
39pF
106pF
tr
21ns
8ns
19ns
tf
24ns
10ns
28ns
RDS(on)
3.3 Ohm
3.3 Ohm
0.98 Ohm
NCP1200
90
80
70
Efficiency %
60
50
40
NCP1200
30
20
10
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Load Current (Amps)
0.8
0.9
1
1.1
1.2
1.3

Three states: Preconditioning, Constant Current, Constant Voltage
[2] Courtesy of Texas
Instruments


Capacity: 2600 mAh
Working Voltage: 7.2V

Peak Voltage: 8.4V

Cut off voltage: 5.5 V

Max Charging Current: 2 Amp

Length: 2.8"

Width: 1.45"

Height: 0.8"

Weight: 3.5 Oz
Linear

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Low Cost
Low Design Complexity
Low Noise
Small size
Poor Efficiency <40%
 High Heat Dissipation

Switching


High Efficiency 80+%
Extended Battery Life
Higher Cost
 Higher Design
Complexity




PCB resides in console
Console affixed to any standard white
cane using a mounting unit
Switches on side of console allow user the
freedom to turn on and off select features
such as audio, GPS, or sonar.
Progress Percentage
Research
Design
Part Selection
GPS
Audio
Progress Percentage
Software
Sonar
Power Supply
PCB Design
0
20
40
60
80
100
Who does what?
Power Supply
Mark/Nick
Sonar
Mark/Nick
Navigation
Matt
Console Design
Mark/Matt
Audio
Matt/Sara
Microcontroller
Matt/Sara
Item
Price
Audio Module
$39.95
Parallax Ultrasonic Distance Sensor
$29.99
Microcontroller + Target Board
$58.95
White Cane
$27.45
Electronic Components
$82.65
Lithium Ion battery
$44.90
Vibration motors
$15.00
Ls20031
$49.99 (3)
SD Card and Breakout Board
$19.99
LSM303
$19.99 (3)
Miscellanious
$200.00
Plexiglass
$45.00
Headphones
$150.00 (2)
PCBs
$700.00
Arduino Uno Test board
$29.99 (2)
Total
$2000
Project Future Costs
$150
Max Budget
$2500





Processor: Upgrade MCU to multicore/phone style
processor or use multiple smaller chips
 Allow for more advanced navigation (Google
Maps)
 Tasks stepping on each other (sonar/navigation)
PCB: Needed second revision on main MCU board
but not enough time to order and populate
Sonar: Second MCU is needed to do the
calculations
Sonar: High side switching needed to get rid of
noise
Sonar: More gain is needed to pick up objects at a
further distance