LED Array with Adam Zysk

1
LED Array with Adam Zysk

• Group 14
• Robert Koch, Victor Lu Thomas Shen
• ECE 445 Senior Design
• April 26, 2006

2
Design Review Specifications

• Purpose
• Research in optical coherence
• Requirements
• 400 SMD Dual Color LEDs
• 3 x 3 layout of LEDs
• Individually controlled LEDs
• GUI and mouse input

3
Revisions to Original Design

• Registers now sink current rather than source
  current
• Clock signal now buffered rather than driving all
  100 registers directly with a single PIC output
• Fans added to relieve overheating

4
Final Features

• 400 SMD Red/Green LEDs
• 31/8 x 31/8 area.
• LEDs individually controllable
• Intuitive software interface
• RS232 communication

5
System Overview

• Hardware
• LED Array Board, Register Boards (x10), Control
  Board
• Software
• PIC program
• Windows program

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The LED Array System
LED Board
Power Supply
Register Boards
Control Board
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LED Board

• Assembled using solder paste and toaster oven
• 400 LEDS in 3 1/8 X 3 1/8 area
• Slightly larger than 3 X 3 to accommodate 2mm
  pin headers on bottom side of board
• Vias filled manually because part shop does not
  plate vias gt connections unstable.

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Register Board
2.54mm Right-Angle Pin Header
2mm Right-Angle Pin Header
74F164APC 8-bit Shift Registers
Bottom View
150 Ohm Surface Mount Resistor
Top View
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Control Board
Connections to Register Boards
Molex Connector to Power Supply
SN74LS125AN Tri-State Buffers
RS232 Connector
Fox F1100 20Mhz Oscillator
MAX232
PIC16F877A Microcontroller
10
Computer Interface

• Programmed using Visual Basic 6
• User Friendly
• Communicates using RS232 Serial interface
• Polls for acknowledge byte from PIC

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Problems and Challenges in Assembling Project

• Design issues
• Length of wires needed to be precise
• Finding suitable connectors
• Time consuming
• 1600 crimps by hand
• Placement of 1600 dabs of solder paste in
  preparation for toasting
• 200 surface mount resistor arrays
• 100 registers
• Filling 800 vias
• Debugging
• Poor solder joints
• Poorly milled PCB

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LED Current Measurements

• Current found by dividing voltage across resistor
  by resistance
• Current output to LED remains approximately the
  same regardless of number of LEDs powered

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Current Variation
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Total Current Consumption Measurement

• Unable to directly measure due to high current
• Connected 1,2 and 3 register boards and measured
  current drawn
• Extrapolated data of what current draw would be
  with 10 register boards

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Total Current/Power Consumption

• Total Power 15.68 x 5 78.42W

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LED Power Consumption
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Resistor Power Dissipation
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Control/Register Power Dissipation

• denotes extrapolated data

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Power Dissipation Distribution
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Temperature
33.1C
25.2C
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Expectations vs. Actual Measurements
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Room for Improvement

• Tweak current limiting resistors to give optimal
  LED operating point (2.2V for green, 2.0V for
  red)
• Out-source LED array board for better via
  connections
• Resistors account for 38 of the power
  dissipation may reduce total power consumption
  by using other means of LED current limitation,
  i.e. using transistors
• Reverse polarity and over-voltage protection

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Acknowledgments
Adam Zysk for the idea Dwayne Hagerman for many
suggestions Mark Smart, Dan Mast, and the other
Part Shop people for help, advice, and
resources Molex for the free sample connector