ECE 477: Digital Systems Senior Design
Last Modified: 11-12-2015
Functional Specification
Year: 2016__ Semester: __spring_ Team: 8_ Project:_TBA Bike Safety Helmet________
Creation Date: __1/20/16_________
Last Modified: January 22, 2016
Author:
Author:
Author:
Author:
_____Mark Hand_________
Email: ______hand0@purdue.edu_________
____Lalit Sudarshan______
Email: ________lsudarsh@purdue.edu_______
____Isaac Jing____
Email: ________jjing@purdue.edu_________
___Pranjit Kalita_____ Email: _____kalita@purdue.edu_______
Assignment Evaluation:
Item
Score (0-5)
Assignment-Specific Items
Functional Description
Theory of Operation
Expected Usage Case
Design Constraints
Writing-Specific Items
Spelling and Grammar
Formatting and Citations
Figures and Graphs
Technical Writing Style
Total Score
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Weight
Points
Notes
x3
x3
x3
x3
x2
x1
x2
x3
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ECE 477: Digital Systems Senior Design
5: Excellent 4: Good
3: Acceptable 2: Poor
Last Modified: 11-12-2015
1: Very Poor 0: Not attempted
General Comments:
Relevant overall comments about the paper will be included here
1.0 Functional Description
The TBA is head-mounted device aimed to give bikers relevant information about surrounding
vehicular traffic for enhancing their safety. We intend to detect probable vehicular hazards in the
vicinity of the user and correspondingly warm them about the seriousness of the posed danger
relative to the closeness between them. Furthermore, our device will be programmed to calculate
tangible information such as relative speed of the impending danger on a character LCD display,
while giving the user some enhanced functionalities such as adjusting the intensity of flashing
lights based on time of day, etc.
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ECE 477: Digital Systems Senior Design
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2.0 Theory of Operation
TBA cyclist HUD utilizes a microprocessor to interface with a few hardwares which input and
output information. The ultrasonic sensors will be used to detect potential hazard behind the user,
as well as provide location and speed information about the hazard. The ultrasonic sensor will
output ultrasonic waves towards the back of the user. If there’s a hazardous object, it will reflect
the ultrasonic back to the device, where the sensor captures the reflected wave. The time
difference (𝑡1 ) between sending out ultrasonic wave and receiving ultrasonic wave will be used
to calculate the distance (𝑑) in between the sensor and the object.
𝑑 ≃ 0.5 × 340 × 𝑡1
When the distance (𝑑) is calculated, the device also compare the difference in distances (𝛥𝑑) at
different time (𝛥𝑡) to calculate the hazard’s approaching speed (𝑣) towards the user.
𝑣 = 𝛥𝑑/𝛥𝑡
The IMU unit will be used to capture the device’s speed, as well as its acceleration. IMU unit
contains a GPS module, and also an accelerometer. The GPS module receives signal from three
or more satellites, and receives distance info, as well as satellite’s location info from the
satellites. Then, the module will calculate the location of the device using those distances, as well
as the satellite’s location. After the location is known, the device can calculate the travel
distances at a given period of time, to calculate its speed. This calculation will not be very
accurate, and the unit will not receive satellite signals when under a tunnel. Accelerometer
measures the acceleration of the device, which can be integrated to calculate the device’s speed
as well. Besides, the accelerometer directly output acceleration info, which will be used to
determine if the user is braking or not.
The photodiode will be used to measure the light exposure of the device. Its connectivity will be
different at different light exposure. This info will be used to determine the display’s brightness.
3.0 Expected Usage Case
The TBA is intended for use by single bikers to monitor the environment around them. Thus, the
environment would comprise of road traffic that may threaten the safety of the user, most notably
being vehicular traffic. We further intend to have sensors on both sides of the user with
corresponding warning devices so the user knows exactly where the danger is located, and how it
is changing relative to time. Thus, the device is mobile with settings to enhance user interface for
changing what information the user is interested in gathering at any particular instant of time.
Since bikers encompass a wide range of ages, we are not making any assumptions about their
capabilities and/or technical competence. This is why we intend to give users additional
functionalities with a friendly user interface for ease of use.
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ECE 477: Digital Systems Senior Design
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4.0 Design Constraints
4.1 Computational Constraints
Our computations will comprise of both on-chip computations and those performed by us. First,
we will use ultrasonic sensors to detect nearby traffic. A GPS module will relay relative position
of the detected object to the user, with the biker and collider speed being measured in real-time
by an Inertial Measurement Unit (IMU) chip. A power management IC will be used to computer
the battery level of the device, while an ambient light sensor will be used to computer brightness
relative to the LCD according to time of day. We will be using a character LCD to display the
calculated information such as speed relative to the danger. Finally, at the core of the warning
would be the vibrators whose frequency will change relative to the information obtained on the
ultrasonic sensors, the GPS module, and the IMU. User interface is expected to be improved by
giving them the ability to change settings on the device. An instance relative to our device would
be the ability to change the sensitivity settings, which will be through a potentiometer.
With regards to memory (non-volatile), due to the dynamic nature of computations and lack of
storage requirements for any collected or computed data, we will not require any memory or
storage device. All our computations should be reasonably well served by the on-chip RAMs of
the various chips mentioned above.
4.2 Electronics Constraints
For this project, there will be quite a few interfaces that will be needed to be included. The first
of which is ultrasonic sensors. This should be a pretty simple interface. There will be two sensors
with the same interface. These will just use two very basic I/O pins. The second interface would
be for the IMU. There will be an I2C connection for this. Another very simple input will be for
power management. This will also just have one simple I/O pin. The ambient light sensor will be
an I2C connection to the processor. as communication will need to go both ways to the device.
The LCD display will be one or more simple I/O pins based on how we decide to create the
HUD. The USB charger will obviously be interfaced using USB. The vibrators will be PWM
outputs that will change frequency based on how far away the hazard is. Lastly, the
potentiometer will be an ATD input, the lower the resistance the more sensitive the we will want
the sensors to be
4.3 Thermal/Power Constraints
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ECE 477: Digital Systems Senior Design
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As this device will placed on top of a human head, it should hopefully remain cool and and not
be too hot. Issues where this may be a lot of heat generated would be where all the connections
are near the display. Therefore we have determined that are target temperature will be about a
hundred degrees. Our project will be battery operated. But it should be pretty efficient and
doesn't have a whole lot of moving parts. Therefore we have determined that the battery life
should be at a minimum of 3 hours. This would give the biker ample time to do any travelling in
a day. The wireless charger means we may have a slightly larger charge time, but we should be
able to charge while the user is out about his/her day.
4.4 Mechanical Constraints
This objective of this project is to design a safety device that can sit comfortably on the helmet of
a biker. Therefore, the product should be well within the size of an average helmet. We will aim
to keep our product within a 4 inch by 4 inch form factor. The device which will sit externally on
top of the helmet should be under 100 grams, including the power source which will be a battery.
Also, since the device will sit externally on the helmet, the device should be waterproof. The
device will use vents on the helmet to be attached firmly.
4.5 Economic Constraints
For this project we will need a microprocessor, some simple displays which shouldn't cost more
then 20 dollars, 2 ultrasonic sensors at 40 dollars each, 2 vibrators at 5 dollars each, an IMU at
30 dollars, power management IC at a few dollars, and various other small electronic
components for another 20 dollars. We will also need a helmet, this will be about 50 dollars. For
all of this combined, plus a little padding we have concluded that our project should be 300
dollars. There are no real competing projects to base our costs of off. The group that previously
did a HUD was for a motorcycle helmet, they set their price for a thousand dollars, which is
considerably different in price from a bicycle helmet.
4.6 Other Constraints
Since TBA cyclist HUD will be used outdoors, the device will need to be rain-proof. The device
will not be required to operate under the water, but will be required to functioning at raining
conditions. The proper rain-proof level would be about IPX-3 or IPX-4.
It is usually also required for outdoor used devices to have IP-1 level dust proof. At the same
time, device such as helmet needs to be physical impact proof. We would like the device to fell
from 1 meter without damaging the device.
5.0 Sources Cited:
Justelation, "IPX Ratings Described | Just{elation}", 2013. [Online]. Available:
http://justelation.com/ipx-ratings-described. [Accessed: 22- Jan- 2016].
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ECE 477: Digital Systems Senior Design
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Parallax "PING))) Ultrasonic Distance Sensor | 28015 | Parallax Inc", 2016. [Online]. Available:
https://www.parallax.com/product/28015. [Accessed: 22- Jan- 2016].
TI, "LM2936 | Single Channel LDO | Linear Regulator (LDO) | Description & parametrics",
2016. [Online]. Available: http://www.ti.com/product/LM2936. [Accessed: 22- Jan- 2016].
AG, "Digital Ambient Light Sensor Proximity Sensor - IR LED in an Optical Module TMD27711 ams", Ams.com, 2016. [Online]. Available: http://ams.com/eng/Products/LightSensors/Ambient-Light-Sensor-Proximity-Detection/TMD27711. [Accessed: 22- Jan- 2016].
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