Table of Contents
Executive Summary ........................................................................................................................ 2
1. Introduction ................................................................................................................................. 3
1.1 Objective ............................................................................................................................... 3
1.2 Motivation ............................................................................................................................. 3
1.3 Background ........................................................................................................................... 3
2. Project Description and Goals .................................................................................................... 5
2.1 Design.................................................................................................................................... 5
2.2 Display .................................................................................................................................. 5
2.3 User Input .............................................................................................................................. 6
3. Technical Specifications ............................................................................................................. 6
3.1 Single Board Computer ......................................................................................................... 5
3.2 Display .................................................................................................................................. 8
3.3 Software ................................................................................................................................ 9
4. Design Approach and Details ..................................................................................................... 9
4.1 Design Approach ................................................................................................................... 8
4.2 Codes and Standards ........................................................................................................... 12
4.3 Constraints, Alternative, and Tradeoffs .............................................................................. 13
5. Schedule, Tasks, and Milestones .............................................................................................. 14
7. Marketing and Cost Analysis .................................................................................................... 15
8. Summary ................................................................................................................................... 16
9. References ................................................................................................................................. 17
Appendix A ................................................................................................................................... 19
HMI Solar Jackets (ECE4007 L01)
i
Executive Summary
The Solar Jackets Club at Georgia Tech will be competing in the 2011 World Solar
Challenge and 2012 American Solar Challenge, and is requesting the development of an HMI
system for the cockpit of their solar car. In order for the system to be suitable for use in the solar
car, the design will focus on compactness, power efficiency, user friendliness, and safety. It will
include two panels of LCDs with pushbuttons and switches, interfacing with the car’s singleboard computers to display vital vehicle information. The displayed information will include
speed, battery gauge, power consumption, clock, cruise control status, temperature, turn signals,
parking break status, and error notifications. The single board computer (SBC) will be restrained
to the TS-7250 since it was previously implemented and used by the Telemetry and Motor
Control groups of the former semester. The pushbuttons and switches will give the driver the
ability to control the cruise control, headlights, and turn signal functions of the car. Even though
this product is designed solely for the Solar Jackets, other universities will be able to use the
code from this project to jump start similar projects in their respective clubs. The total expected
costs of this project is estimated to be about $245 to purchase all parts.
HMI Solar Jackets (ECE4007 L01)
1. Introduction
The HMI and Cockpit team is requesting $245 to design a human-machine interface
(HMI) system for the Georgia Tech Solar Jackets’ solar race car. The Solar Jackets will be
competing in the 2011 World Solar Challenge racing event[1] and they are in need of a compact
and power efficient HMI system.
1.1 Objective
The HMI system will receive data from the car’s telemetry and motor control singleboard computers (SBC.) The telemetry and motor control SBCs store the car’s vital and motor
information, respectively. Power efficient display devices will be used to display information
from both SBCs to the driver. The HMI system will also include pushbuttons and switches. The
status of each pushbutton and switch will be recorded, stored, and used by other processes on the
telemetry and motor control SBCs to determine the required action.
1.2 Motivation
The HMI system will display vital information needed for efficient operation of the solar
race car to its driver. Pushbuttons and switches will allow the driver to interact with the car. The
HMI system will be compact and power efficient, ideal for the Solar Jackets’ solar race car.
1.3 Background
The HMI subsystem will be a part of the solar car’s overall computer system, which
includes the telemetry, motor control, solar cell, and battery management subsystems. The HMI
HMI Solar Jackets (ECE4007 L01)
system will communicate with and receive data from the telemetry and motor control SBCs. The
telemetry, motor control, and solar cell subsystems are ongoing projects, and the battery
management subsystem is currently being designed.
1.3.1 Telemetry
The telemetry subsystem collects all vital information of the solar race car through lowpowered sensors and controllers, and stores it in an SBC. The Solar Jackets team use this
information to make proper decisions for the car’s operation. The collected information includes
the battery voltage and current, the motor controller voltages and currents, the ambient
temperatures inside and outside of the car, and the vehicle speed[2].
1.3.2 Power Management (Solar Cell)
The power management subsystem monitors the car’s solar cell arrays in order to extract
maximum power to charge the car’s batteries. A power switching circuit controlled by a
microcontroller provides the optimal impedance across the solar array to extract maximum
power. The microcontroller stores the solar cell array’s input and output voltages, current, and
power[3].
1.3.3 Motor Control
The motor control subsystem controls the solar race car’s motor. Functions of the motor
control subsystem are regenerative braking, cruise control, and power management of the motor.
A motor controller unit obtains real-time data about the motor, which is stored on an SBC. Data
stored on the SBC include motor temperature and power, speed, cruise control, and braking[4].
The SBC sends motor control commands to the controller unit of the motor.
HMI Solar Jackets (ECE4007 L01)
2. Project Description and Goals
Information from the telemetry and motor control SBCs will be displayed in the cockpit.
Pushbutton and switch statuses will be recorded on each SBC, and used by programs to
determine the required action. The HMI system will be composed of the following components:

Display devices

Single board computer

Pushbuttons

Switches
2.1 Design
The Cockpit and HMI team aims to create an HMI system suitable for a solar race car.
Design of the HMI system will focus on the following:

Compactness

Power efficiency

User friendliness

Safety
2.2 Display
The display devices will show important and vital information to the driver of the solar
race car. The display devices will include the following items:

Speed
HMI Solar Jackets (ECE4007 L01)

Battery gauge

Power consumption

Clock

Cruise control status

Temperature

Turn signal indicator

Parking brake indicator

Error notification
2.3 User Input
The user will interact with the car through pushbuttons and switches. The pushbuttons
and switches will allow the driver to make the following actions:

Cruise control

Headlights on/off

Turn signal on/off
3. Technical Specifications
3.1 Single Board Computer
Since the Telemetry and Motor Control groups have already done considerable work on the TS7250 SBC, we will use the same one in our design. The specifications of the TS-7250 are below.
HMI Solar Jackets (ECE4007 L01)
Table 1 - Technologic TS-7250 Linux SBC specifications
Features
Specifications
Processor
200MHz ARM9 CPU
Flash Memory
32MB NAND Flash
Random Access Memory
32MB SDRAM
USB
USB 2.0 (12 Mbit/s Max)
Ethernet
10/100 Ethernet interface
Interfaces
20x DIO lines, USB 2.0, SPI,
Dimensions
3.8” x 4.5”
Power
5V DC @ 400mA
Operating Temperature
-40° to +70°
OS
Linux
HMI Solar Jackets (ECE4007 L01)
3.2 Display
Table 2 - Desired LCD Specifications.
Features
Specifications
Resolution
100x50 pixels - 150x75 pixels
Interface
SPI
Supply Voltages
3.0V to 3.3V
Power Consumption
.3 mW - 1 mW
Operating Temperature
-20°C to +70°C
Dimensions
50x40mm - 100x80mm
HMI Solar Jackets (ECE4007 L01)
3.3 Software
Table 3 - Desired Software Specifications.
Features
Specifications
Saved data format
CSV
Programing Language
C
CPU load
10% to 25%
Poll Times
Pushbuttons
5-10 per sec
Switches
2-5 per sec
Temperatures
1 per sec
Speed
5-10 per sec
Battery Power
2-3 per sec
4. Design Approach and Details
4.1 Design Approach
A top down explanation of the design approach is presented below.
4.1.1 Overall Architecture
The human interface of the solar car will contain two printed circuit boards (PCBs), each with
two LCDs and four pushbuttons. The two PCBs will separately show telemetry and motor
HMI Solar Jackets (ECE4007 L01)
control data. This data comes from two separate SBCs programmed by the Solar Jackets
Telemetry and Motor Control groups. Programs written in C will reside on both SBCs and
control the data displayed onto the LCDs. The LCDs and pushbuttons will be connected to the
SBCs via a serial interface. This will allow for scalability and future additional buttons without
extensive rewiring. A serial interface will result in data being transferred over one cable from the
SBC to the PCB. The pins on the PCB will distribute the data to its intended recipient, such as
the LCDs and the pushbuttons. Figure 1 shows this architecture.
Figure 1. Overall architecture of design.
HMI Solar Jackets (ECE4007 L01)
4.1.2 PCB Displays
The two PCBs will be identical except for the source of data. Therefore, the rest of the
document will refer to just one PCB. The DOGM128 LCDs will be mounted onto the PCBs.
These displays are 55 x 46mm in dimension and consume 0.496 mW of power when there is no
backlight [7].
Figure 2. A photograph of the DOGM128 LCD.
Below are possible set-ups of displaying information on the LCDs.
HMI Solar Jackets (ECE4007 L01)
Figure 3. PCB design example with four pushbuttons and two LCDs.
The pushbuttons will be used to set the cruise control, turn signals, headlights, and scroll through
error messages.
4.1.3 Serial Interface
The LCDs will be connected to the TS-7250 SBCs via a serial interface [9]. The TS-7250 has
two serial ports, COM1 and COM2. The TS-7250 will gather information from sensors attached
to its 20 digital input/output ports. This information will be stored on the 32MB on-board flash
memory. Software will be written to transmit this information from the TS-7250 to the LCDs
over serial ports using the RS-232 communication standard. The TS-7250 supports baud rates up
to 230.4Kbaud [5]. Baud rate is “the measurement of the number of times per second a signal in
a communications channel changes”[6]. For the types of data we wish to show, a buad rate of
230.4Kbaud is sufficient.
4.1.4 Software
Several programs written in C will control the LCDs. The programs will be self-executable
so that they run as soon as the SBC is turned on. This feature will save the driver time if the
electrical systems need to be restarted.
An application programming interface (API) will be created for future developers to add new
features to the car. The API will create a format for storing telemetry and motor control data.
This format will allow programs to parse through large amounts of information and display the
required data. This standard format will also allow multiple programs with different
functionalities to pull data from the same source file.
Along with displaying already gathered data, programs will poll incoming data from the
serial interface to detect whether any of the pushbuttons have been used. The functionality of
HMI Solar Jackets (ECE4007 L01)
each pushbutton does not need to be specified. As long as the program can record a change in
status in the pushbutton, future programs can be written to add functionalities that the Solar
Jackets require.
4.2 Codes and Standards
The regulations set forth by the World Solar Challenge and the American Solar
Challenge that affect embedded systems in the car are as follows [8]:
1. The drive must have vision in all directions to the satisfaction of the Chief Scrutineer.
2. All equipment must be powered by solar panels.
3. If cruise control is allowed, then engaging the breaks must automatically turn off the
cruise control.
4.3 Constraints, Alternative, and Tradeoffs
Display
A major design constraint for this project is limited space in the Solar Jacket’s car. The PCBs
must be less than 1 foot (=0.3 meter) in width and even less in height. This constraint rules out
the use of larger LCDs that would allow for a better user interface. Since the car is operated
solely on solar power, the racing team would benefit if the least power is consumed by
electronics and most of the power is used for driving the motor. This constraint rules out the
usage of backlight LCDs due to their higher power consumption than non-backlight LCDs as the
DOGM128 series. An alternative to multiple LCDs is the use of LEDs and a single small LCD.
Since the LEDs are relatively smaller than the second LCD, the advantage would be smaller size.
HMI Solar Jackets (ECE4007 L01)
However, due to reasons of scalability and future additional features, the PCBs will host dual
LCDs.
Another constraint placed on the LCDs is that they must be daylight readable. Since the
solar car will be operated during the daytime and the canopy of the car allows sunlight into the
cockpit, the LCDs will most likely be under direct sunlight during most of the race. The
DOGM128 series LCDs are daylight readable. There are alternative LCDs that fit these
constraints; however, the Motor Control group already used the DOGM128 series LCD to
interface with their SBC last semester. Since this product has been shown to work well with TS7250, it will be used in this design.
Embedded Computing
The Telemetry and Data Control groups use the TS-7250 by Technologic Systems for
their embedded computing. Since there is limited space in the solar car, this design will use the
same TS-7250 so that hardware can be minimized.
5. Schedule, Tasks, and Milestones
Refer to Appendix A for the Gantt chart of project schedule.
6. Project Demonstration
The final project will be demonstrated in the senior design laboratory of the Georgia Tech
campus by members of the Solar Jackets HMI and Cockpit group. The testing procedure will
include parsing through the test data on the SBC. This information will be shown on the LCD
connected to the SBC. This will confirm the connectivity and interfacing ability of the LCD to
HMI Solar Jackets (ECE4007 L01)
communicate with the computer. The pushbuttons on the panel will be used to toggle the
information displayed on the screens to show their capability to execute commands in the
computer. When a pushbutton state change is recorded, the SBC will perform a specific
predetermined function. This will demonstrate the functionality of the pushbuttons. These
predetermined functions will include showing text on the LCD screen which confirm that a
specific pushbutton was pressed.
7. Marketing and Cost Analysis
7.1 Marketing Analysis
When considering the importance of driver communication and control of a vehicle, the
HMI system in solar cars becomes a highly marketable component. The HMI system being
designed for the Solar Jackets vehicle is for the sole purpose of the Solar Jacket’s participation in
the World Solar Challenge and American Solar Challenge competitions. The final design of the
HMI system implemented in the Solar Jackets car can be marketed as a basic design interface for
other university students working on similar projects. This would not be a priced product.
Students from other universities will be able to use the API created to help jump-start their
projects.
7.2 Cost Analysis
The development of the HMI system is estimated to have a total cost of $245 for the
purchase of all parts. An overview of these parts and pricing is shown in the table below.
HMI Solar Jackets (ECE4007 L01)
Table 4 - Cost Analysis Table
8. Summary
Three DOGM 128 series LCDs have been bought and are available for use. A TS-7250
SBC will be ordered immediately so that we can begin testing the code from the Motor Control
group. The group will also attend PCB layout classes as soon as they are resumed. While the
parts are being ordered, the Motor Control group's code for displaying data on the DOGM 128
LCDs will be examined and a format for the source data files will be created after cooperation
with other Solar Jacket teams.
HMI Solar Jackets (ECE4007 L01)
9. References
[1] Georgia Tech Solar Jackets, “Solar Jackets”. [Online]. Available:
http://solarjackets.gatech.edu/projects/racer. [Accessed: Feb. 20, 2011].
[2] W. Mann, F. Farooqui, H. Chang, "Solar Jackets Telemetry Project," 2010. [Online].
Available:
http://www.ece.gatech.edu/academic/courses/ece4007/10fall/ECE4007L01/ws1/files/sjt_summar
y.pdf. [Accessed: Feb. 20, 2011].
[3] N. Joshi, A.Haile, G.Colon, M. Calotes, M. Lu, "Solar Power Array Managementt," 2010.
[Online]. Available:
http://www.ece.gatech.edu/academic/courses/ece4007/10fall/ECE4007L01/ws2/spam_project_su
mmary/projectsummary_final.pdf. [Accessed: Feb. 20, 2011].
[4] A. Jenkins, J. Oatts, D. Thompson, E. Kfir, P. Rybakov "Motor Controller," 2010. [Online].
Available:
http://www.ece.gatech.edu/academic/courses/ece4007/10fall/ECE4007L01/ws3/final_project_su
mmary.pdf. [Accessed: Feb. 20, 2011].
[5] Technologic Systems. (2010, January). TS-7250 Hardware Manual (2.6 Ed.) [Online].
Available: http://www.embeddedarm.com/documentation/ts-7250-manual.pdf [Accessed: Feb.
20, 2011].
HMI Solar Jackets (ECE4007 L01)
[6] “Difference Between Bit Rate and Baud Rate,” Top Bits, Jul. 2010. [Online]. Available:
http://www.tech-faq.com/difference-between-bit-rate-and-baud-rate.html [Accessed: Feb. 20,
2011].
[7] DOGM. (2008, October). DOGM Graphic Series Datasheet. [Online]. Available:
http://www.lcd-module.com/eng/pdf/grafik/dogm128e.pdf [Accessed: Feb. 20, 2011].
[8] World Solar Challenge. (2010, August). Technical Regulations for 2011 World Solar
Challenge Event. [Online]. Available:
http://www.worldsolarchallenge.org/participants/regulations [Accessed: Feb. 20, 2011].
[9] Technologic Systems. (2009, June). TS-7250 Datasheet. [Online]. Available:
http://www.embeddedarm.com/documentation/ts-7250-datasheet.pdf [Accessed: Feb. 20, 2011].
HMI Solar Jackets (ECE4007 L01)
Appendix A
Table A1 – Gantt Chart Details
HMI Solar Jackets (ECE4007 L01)
HMI Solar Jackets (ECE4007 L01)
HMI Solar Jackets (ECE4007 L01)