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EEL 4924 Electrical Engineering Design 2 (Senior Design)

Final Design Report April 25th 2012

Project: Vehicle LED Display

Members: Skylar Stroman & Kaitlin Fish-Stuhl

Project Abstract

The project is an LED matrix display for the back window of car that will interface with an

Android smartphone application through Bluetooth wireless. The device can be used to notify

other drivers of road hazards and to facilitate general communication while driving.

Additionally, this device can be used in non-driving settings where a user needs to be able to

update an LED display wirelessly and easily.

The Android application will use the phone’s built-in voice recognition to provide the customer

with an easy way to update the display without interfering with driving. The app will also

include an easy-to-follow user interface.

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Table of Contents

Tables and Figures ..........................................................................................................................3

Project Features and Objectives .....................................................................................................4

Concept/Technology Selection .......................................................................................................4

Flowcharts and Diagrams ................................................................................................................6

Division of Labor .............................................................................................................................8

Bill of Materials ...............................................................................................................................9

Gantt Chart......................................................................................................................................9

Appendices .................................................................................................................................... 10

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Tables and Figures

Figure 1: Block Diagram ..................................................................................................................6

Figure 2: 25 LED Array .....................................................................................................................6

Figure 3: LED Driver (ICM7228).......................................................................................................6

Figure 4: First Half of LED Driver Circuit .........................................................................................7

Figure 5: Second Half of LED Driver Circuit .....................................................................................7

Figure 6: Power and Solar Charging Circuit ....................................................................................8

Table 1: Division of Labor ................................................................................................................8

Table 2: Bill of Materials .................................................................................................................9

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Project Features and Objectives

This project design was originally intended as a novelty item for a vehicle by which people can

communicate with other drivers through an LED display. However, this device can also be used

in any situation where wireless update of a LED display is required.

Features of the project include:

Easy update via phone

o The user can use a simple user-interface via an android application

o Information transmitted via Bluetooth

Aesthetically pleasing appearance

o No view obstruction, slim, small box

300 LEDs in a 12 digit, 5x5 matrix display

Three different power options

o 3 Battery packs rechargeable via solar panels

o 12 Volt Car Jack

o Wall outlet plug

Concept, Technology and Architecture

We have chosen to use an Android application to interface with the LED matrix for wireless

update. We chose Android because we have access to an Android phone for testing. This will

allow the user to take advantage of the user friendly nature of the android application.

The phone will communicate with the display through Bluetooth technology. The Class 2

Bluetooth on most phones provides a relatively small range (~30 ft) so the display will rarely be

able to be used by anyone other than the driver or passengers. The Bluetooth signal will

transmit the display information to a receiver attached to an MSP430 microprocessor. We have

chosen the MSP430 because of our previous experience, live-debugging, number of pins, and

low power options.

The microprocessor will update the LED display through an LED driver system. The LED driver

system consists of 8 bus extenders (PCF8574) and 6 common anode LED drivers (ICM7228A).

The PCF8574 is a bus extender for bi-directional busses, such as the I/O lines on the MSP430,

which gives access to 8 more I/O pins per chip. These additional 32 I/O pins will be used to

control the LED drivers. This system allows us to use only eight pins from the MSP430 to drive

300 LEDs. Part of the LED driver system is shown in Figures 2 and 3. Figure 2 is a schematic of 64

out of 300 of the LEDs. The other LEDs will be laid out in groups of 25 in the same manner. Each

group of 8 is a digit for the purpose of using the LED driver, and each of those 8 LEDs is

connected with a common anode. The corresponding a, b, c, d, e, f, g, and decimal point (dp)

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segments of each digit are connected together, then connected to the corresponding pin of the

LED driver. Figure 3 shows the LED driver with its attachments. The bus extender will be

connected to the control pins of the LED driver.

The display itself can be powered by three different sources. The first option is from 3

rechargeable battery packs. These batteries will be charged by solar panels that will be

mounted on top of the display. This will make the display a standalone device and prevents the

need to run wires though the car. The second power option is through the 12 volt car jack. The

unit will then be able to run at any time of day and in any kind of weather. Finally, the last

option is through a wall outlet. This allows the unit to be used inside for other various

applications.

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Flowcharts and Diagrams

Figure 1: Block Diagram

Figure 2: 1/12 of LED array layout – 25 LEDs out of

300. Connections to ICM7228 (LED driver) shown Figure 3: LED Driver ICM7228

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Figure 4: ½ of LED Driver Circuit Design

Figure 5: ½ of LED Driver Circuit Design

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Figure 6: Power and Solar Charging Circuit

Division of Labor

Skylar Stroman Kaitlin Fish-Stuhl

Power Circuitry Android Application

Solar Charging Bluetooth Communication

Display Design/Construction LED Drivers

Microprocessor Programming Microprocessor Programming

PCB Design PCB Design

Table 1: Division of Labor

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Bill of Materials

Part Description Amount Cost/Unit (USD)

Total Cost (USD)

Grand Total (USD)

RN-42 Bluetooth Chip 1 17.00 17.00

ICM7228 LED Driver 6 4.21 25.26

PCF8574 Bus Extender 8 0.63 5.04

MSP430g2553 Microprocessor 1 4.30 4.30

XBee Wireless Com. Chip

2 22.95 45.90

Resistor Misc. 4 0.08 0.32

Capacitor Misc. 6 0.05 0.30

Diode Misc. 11 0.10 1.10

LED Misc. 300 0.08 24.00

LM3940IT-3.3 Voltage Regulator

1 1.65 1.65

LM317KC Voltage Regulator

2 3.22 6.44

Battery Misc. 12 1.49 17.88

12 Volt Car Jack Misc. 1 8.95 8.95

Solar Panel Misc. 4 7.50 30.00

Acrylic Plastic Sheet

Misc. 2 17.99 31.98

220.12

Table 2: Bill of Materials

Gantt Chart

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Appendix A: Experimental Test Plans

LED Driver Tests:

First establish that the LEDs can be written to appropriately by testing with a simple function.

After digits are modifiable, enter array of characters, as would be received from phone, and have the

program break the array into individual characters to be output to the LEDs.

Android App Tests:

Establish a simple user interface, and test by loading the app to an Android phone or run time

environment.

Write a simple program to send output to the Bluetooth receiver module on the main circuit board to

verify functionality.

After simple messages work, the app, if time allows, will be expanded to include voice recognition, using

the phone’s built-in voice recognition system. The program will translate the message into an array of

characters, which will then be sent to the LED drivers.

Bluetooth Tests:

First test for simple transmission using debug mode in Code Composer- make sure the Bluetooth

receiver module connected to the MSP430 can receive information from the phone.

After transmission is established, send simple canned message arrays of characters from the phone to

the MSP430, then upgrade to voice recognition.

Solar Panel Charging Circuit and Power Management System Tests:

Determine an adequate configuration of our solar panels that will provide a voltage higher than that of

our batteries and enough current to show that the batteries are charging.

Drain the batteries and insert them into the circuit to determine if they are charging. Charge the

batteries to their peak voltage to make sure it is possible.

Insert the fully charged batteries into the entire circuit to determine if there is enough power for the

entire device by powering up all the LEDs at the same time for a “worst case scenario” test. Measure the

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speed of voltage decay from the batteries to estimate the fastest time that the batteries could be

discharged.

Appendix B: Software Flowcharts

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