design project - college of engineering - purdue … · web viewthe ability to wirelessly transmit...

ECE 477 Digital Systems Senior Design Project Rev 8/09

Homework 3: Design Constraint Analysis and Component Selection Rationale

Team Code Name: Blinkers++ Group No. 5

Team Member Completing This Homework: Ben Carter

E-mail Address of Team Member: bjcarter @ purdue.edu

NOTE: This is the first in a series of four “professional component” homework assignments, each of which is to be completed by one team member. The body of the report should be 3-5 pages, not including this cover page, references, attachments or appendices.

Evaluation:

SCORE DESCRIPTION

10 Excellent – among the best papers submitted for this assignment. Very few corrections needed for version submitted in Final Report.

9 Very good – all requirements aptly met. Minor additions/corrections needed for version submitted in Final Report.

8 Good – all requirements considered and addressed. Several noteworthy additions/corrections needed for version submitted in Final Report.

7 Average – all requirements basically met, but some revisions in content should be made for the version submitted in the Final Report.

6 Marginal – all requirements met at a nominal level. Significant revisions in content should be made for the version submitted in the Final Report.

* Below the passing threshold – major revisions required to meet report requirements at a nominal level. Revise and resubmit.

* Resubmissions are due within one week of the date of return, and will be awarded a score of “6” provided all report requirements have been met at a nominal level.

Comments:Comments from the grader will be inserted here.


1.0 Introduction

Blinkers++ is an inter-car communication system that provides a more dynamic and intuitive

method of communication. The user will interact with the device using a capacitive touch array

that will be able to accept and interpret multiple touches. The output for the device will be

displayed using coordinated LED patterns associated with the interpreted gesture. For example,

one finger swipe to the rear would indicate gratitude for letting the driver enter traffic. The

corresponding LED pattern would be a smooth pulse of blue light on the rear LEDs. Another

example would be a two finger swipe to the front to indicate to other drivers the intent to parallel

park and it is okay to pass now. The corresponding LED pattern for this gesture would be

scrolling chase of green LEDs from the rear to the front along both sides of the car indicating a

“clear to pass” message. Finally, in the event of a sudden stop, Blinkers++ will use its LED

array to alert surrounding drivers with a sharp red light.

1.1 Updated PSSCs

1. The ability to determine direction of a finger sweep on a touch pad array.

2. The ability to determine the number of fingers used on a touch pad array.

3. The ability to produce at least two meaningful LED patterns.

4. The ability to determine force of acceleration on a car.

5. The ability to wirelessly transmit data from the multi-touch signal processor to the

LED cluster controllers

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2.0 Design Constraint Analysis

The Blinkers++ design features many constraints that require early attention. The inputs

from the capacitive touch array will need to be measured and interpreted into meaningful digital

data. Also, the real-time application of Blinkers++ requires the time elapsed between completion

of the gesture and initiation of the output LED pattern to be minimal. Thus, the processing of the

large amounts of data from the capacitive touch array will need to be accomplished by a fast

processor. Since the LED patterns will not be controlled by the multiple touch signal processor,

we will require another type of controller to act as the coordinator for the LED drivers. This

controller will need the appropriate interface capabilities to work with the LED drivers and also

receive the wirelessly transmitted data from the multiple touch signal processor.

2.1 Computation Requirements

In order for the device to be effective, it will need to reliably and quickly recognize the

gesture swiped across the capacitive touch array. This will entail accepting a large number of

inputs, on the order of 256 8-bit data values, from the capacitive touch array. The multiple touch

signal processer will then need to determine the number of fingers used in the user’s swipe

across the pad. This may be accomplished with a sum of the values returned from the touch

array. Another possible algorithm involves 2-D image processing. The team is currently

considering filtering the image with a difference filter, which will be computationally intensive.

Next, the device will need to calculate the average direction in which the finger(s) moved. All of

this processing needs to happen rapidly as Blinkers++ is intended to be used in real-time and

accordingly, keeping the total time elapsed from gesture completion to initiation of LED output

under 500ms would be desirable.

2.2 Interface Requirements

From the multiple touch signal processor, there will be a need for two lines to act as

master on the I2C interface to the 5 capacitive touch controllers and three or four wires for

UART interface to the RF transmitter. From each LED cluster controller, there will be three or

four wires for the UART interface to the RF receiver and two lines for master mode I2C

interface to the 14 LED driver chips. The team believes that the device will probably require

optical isolation for the I2C lines since they will be spanning the length of the LED strips. 32

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I/O pins on the capacitive touch controllers will be connected to a trace on a PCB which will act

as our capacitive touch array and two will be used to act as slaves on the I2C interface. 15 of the

16 PWM channels will be drive the 5 LEDs and two more pins on the LED driver chips will be

used as slaves on the I2C interface.

2.3 On-Chip Peripheral Requirements

For the multiple touch signal processor accepting and interpreting the user input, it will

require one UART interface for the RF transmitter and one I2C interface to receive all the data

from the multiple capacitive touch controllers. For the capacitive touch controllers, they will

require a capacitive touch peripheral to activate and charge the capacitive touch inputs and an

I2C interface to pass the data to the signal processor. For the LED cluster controllers, they will

require one UART interface for the RF receiver and one I2C interface to instruct the 14 LED

drivers it will be responsible for. The team also anticipates needing a few 8-bit or 16-bit timers

to coordinate the LEDs effectively.

2.4 Off-Chip Peripheral Requirements

Blinkers++ will require many off-chip peripherals, but mostly due to replication. The

capacitive touch array will be a 16x16 matrix of traces on a PCB which will be energized and

measured by our capacitive touch controllers. This will require 42 LED drivers to drive the

LEDs surrounding the cars exterior. There will also be one RF transmitter to send the interpreted

signal from the multiple touch signal processor to the LED cluster controllers and three RF

receivers to accept the transmitted signal in each of the LED strips. Finally, 210 tri-color LEDs

with high luminescence will surround the car’s exterior for output.

2.5 Power Constraints

The user input module from will be powered from the 12V DC power supply/cigarette

lighter standard in most vehicles. Because the current draw on the car battery from Blinkers++

will be many magnitudes smaller than the current draw from other devices, we will be treating

the 12V DC power supply as a regulated power supply. From there, the team will need to

regulate the power supply from 12V down to 3.6V for the user input module

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The 3 LED strips will be powered from the car battery directly. Again, we the car battery will be

treated as a regulated 12V power supply and thus the team will need to regulate the voltage to 5V

for the LED output modules. It is also important to note that each of the projected 210 LEDs

will draw 20mA of current through each of its three colors, although instances where all 210 are

operating at the same time and at full power will never happen under normal conditions.

2.6 Packaging Constraints

The device when mounted on a car will consist of exterior and interior components. Inside

the car, we will place the user input module. The user input module will consist of the capacitive

touch array and the PCB holding the 5 capacitive touch controllers, the multiple touch signal

processor, and an RF transmitter. This module will be enclosed so that only the capacitive touch

array is easily accessible and should be flat enough so that it can be mounted on the steering

wheel with straps or some other mounting mechanism. The overall appearance of the packaging

inside the vehicle should attempt to not visibly stand out from the cars already existing interior

design. There will need to be a power cord from the back of the interior module that can be

plugged in the 12V DC power plug standard in most vehicles.

The exterior of the vehicle will be affixed with 3 strips of tri-color LEDs that must be

enclosed in a weather proof diffuser. The strips will also need to be capable of being temporarily

mounted on the top rim of the car in a wreath-like fashion, and yet should not be liable to

slipping off during travel. Keeping the exterior strips of LEDs thin and lightweight will help and

a potential mounting plan is to use permanent magnets. Inside each of the three weatherproof

diffusers will be 14 PCBs, each with one LED driver chip and 5 tri-color LEDs, all connected

with the two-wire I2C interface. One of the PCBs will also include the RF receiver and

microcontroller in charge of coordinating the LEDs in the strip. Each strip will require a power

cord to be hooked up to the car battery.

2.7 Cost Constraints

At this time, the designers of Blinkers++ are unaware of any competing products, which is

reasonable since the project itself is illegal in many countries due to exterior-lighting-on-vehicle

laws. The expected cost of Blinkers++ is anticipated at approximately $340 to manufacture. By

comparison, just acquiring a multiple touch development kit by itself was quoted to the team as

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$999 by Stantum. Similarly, a Streetglow Multicolor LED Kit with wireless remote costs

$284.97, although it cannot control the individual LEDs with the precision we will be able to

[1].

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3.0 Component Selection Rationale

3.0.1 Multiple Touch Signal Processor

The multiple touch signal processor will be accepting many bytes of data from the array of

capacitive touch controllers, and it has to do this in a timely manner. This will require a DSP

that has loads of RAM and a modest to large amount of Flash. We also required this DSP to

have at least one I2C line for controlling the capacitive touch controllers. A UART interface

will be required as well, since after processing, the multiple touch signal processor will

communicate to the LED cluster controllers the outputs requested by the user. The two best

choices to fit the design constraints were the Microchip’s dsPIC33FJ256MC710 and Analog

Devices’ ADSP-BF512. Both fit the design for RAM size. The major differences are that the

Blackfin can execute multiply and accumulate instructions much faster, on the order of 20 times

faster, although it requires interfacing external memory for program memory [2]. Meanwhile,

the dsPIC33 offers adequate processing speed at 40MIPS as well as well as enough program

memory and interface capabilities [3]. The dsPIC33 also offers 256Kbytes of RAM. Perhaps

the deciding factor is the larger availability of PIC development tools at the team’s disposal.

3.0.2 LED Cluster Controllers

Our LED cluster controllers require little computing power and basically require enough

program memory to load preset LED driver channels in a coordinated fashion. Thus, adequate

flash memory along with some reasonable timers and interfaces will efficiently control our

outputs. Two microcontrollers that fit the design’s needs were Microchip’s PIC18F14K50 and

the Freescale MC68HC908JL16. These 8-bit processors both offer sufficient amounts of Flash

at 16Kbytes and both support the required UART and I2C interface [4], [5]. However, since the

dsPIC was selected for the multiple touch signal processor, keeping everything in the PIC

programming model will ease the software design of two different applications on two different

controllers.

3.0.3 Capacitive Touch Input Controllers

The Blinkers++ team elected to use the Cypress CY8C20666 CapSense controller since

the project revolves around the multiple touch input realized by the array of traces on a PCB.

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Given the intended plan of action and amount of help given to the team from Cypress both

technically and financially (They offered to donate the chips), the CY8C20666 makes the most

sense for the project.

3.0.4 LED Driver Chips

The TLC59116 was selected due to its capacity to control up to 16 PWM channels at a

time [6]. The current LED driving design calls for using 15 channels on each LED driver to

operate 5 tri-color LEDs. Another added benefit of the TLC59116 is its ability to be integrated

with many other LED drivers like it over an I2C interface.

3.0.5 RF Transmitter

Wireless transmission of the user input to the LED output clusters is important to limit

the amount of wires needing to be navigated from the steering wheel, through small gaps in the

cars exterior, to the LED strips on top of the car. The MO-SAWR-AS315M operates at 315MHz

providing transmission of 100 meters in an obstacle free setting [7].

3.0.6 RF Receiver

Each LED cluster will need to receive the interpreted data from the user input from the

multiple touch signal processor. This will be achieved with the MO-SAWR-AS315M’s

complement, the MO-RX3400-A315M.

3.0.7 Accelerometer

One safety feature that Blinkers++ will have is the ability to register sudden stops and

output a larger warning when used in combination with the brake lights already on current

vehicles. For this purpose, an Analog Devices ADXL325 has been selected. This decision was

based on the range of force detected being 5 g over 3 axes and that the device can be operated at

3.6V, which is the voltage at which the user input module will be operating[8].

3.0.8 Capacitive Touch Inputs

The inputs read by the capacitive touch controllers will be physically realized in the PCB

design. The array of touch inputs will be designed and addressed in subsequent documentation.

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4.0 Summary

Blinkers++ is subject to many design constraints due to its large computational load and

numerous quantities of individual inputs and outputs. Because the device hopes to operate in

real-time, efficient processing and data transmission is key, and lead to the selection of three

different controllers, as well as LED driver chips, an accelerometer, and wireless transmitters and

receivers.

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List of References

[1] UrbanNeonCarLights, “Streetglow 3 Million Color LED Kit with Wireless Remote,” http://www.urban-neon-car-lights.com/car-lights/streetglow-lightstrike-3millioncolor-kit.html, [Accessed Sept. 18, 2009]

[2] Analog Devices, “Blackfin Embedded Processor,” ADSP-BF512/BF514/BF516/BF518(F) datasheet, Aug 2009

[3] Microchip Inc. “High Performance, 16-bit Digital Signal Controllers,” dsPIC33FJXXXMCX06/X08/X10 datasheet, Jul 2007 [Revised Mar. 2009]

[4] Microchip Inc. “20-Pin USB Flash Microcontrollers with nanoWatt XLP Technology,” PIC18F13K50/14K50 datasheet, May 2008 [Revised Apr. 2009]

[5] Freescale, “M68HC08 Microcontrollers,” MC68HC908JL16 datasheet, Nov. 2005

[6] Texas Instruments, “16-Channel Fm+ I2C-Bus Constant-Current LED Sink Driver,” TLC59116 datasheet, Feb. 2008 [Revised Jul. 2008]

[7] Holy Stone Enterprise Co., Ltd, “SAW Resonator Transmitter Module,” MO-SAWR-AS315M datasheet, Jun. 2004

[8] Analog Devices, “Small, Low Power, 3-Axis ±5 g Accelerometer,” ADXL325 datasheet, Aug. 2009

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IMPORTANT: Use standard IEEE format for references, and CITE ALL REFERENCES listed in the body of your report.

ECE 477 Digital Systems Senior Design Project Fall2008

Appendix A: Parts List Spreadsheet

Vendor Manufacturer Part No. Description Unit Cost Qty Total CostMouser Microchip dsPIC33FJ256MC710 16-bit DSP MCU hybrid 9.94 1 9.94Mouser Microchip PIC18F14K50 8-bit microcontroller 2.87 3 8.61Mouser Cypress CY8C20666 CapSense Controller 3.61 5 18.05Mouser Texas Instruments TLC59116 LED driver chip 2.01 42 84.42Sparkfun Holy Stone Enterprises MO-SAWR-AS315M RF transmitter @ 315MHz 3.95 1 3.95Sparkfun Holy Stone Enterprises MO-RX3400-A315M RF receiver @ 315MHz 4.95 3 14.85Analog Devices Analog Devices ADXL325 3 axis 5g accelerometer 3.44 1 3.44Digikey Lumex

Opto/Components IncSML-H1505SIUBUBCTR

Tri-Color LEDs 0.93 210 195.30

TOTAL 338.56

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ECE 477 Digital Systems Senior Design Project Fall2008

Appendix B: Updated Block Diagram

Disclaimer: Some values on the current block diagram are subject to change (e.g. # of capacitive touch inputs, # of CapSense controllers)

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