Electrical and Computer Engineering

iLights

Nick Wittemen, EE

Chris Merola, EE

José Figueroa, EEMatt Ryder, EE

Comprehensive Design Review

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Our Design iTunes Plug In PC User Interface Phase Controlled Lighting Controls multiple

incandescent lights Provides interactive

listening environment

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Block Diagram

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iTunes Plug-in

Dynamic Link Library (.DLL) file loaded by iTunes Runs as a visualizer plug-in, able to access

frequency data Exports frequency data via COM port at rate of

visualizer update (set to max, up to 60 fps)

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Project Sources

Visual Studio Project• Based on VizKit, open source framework built to iTunes

Visualizer SDK guidelines• Provides well documented method for implementing an

OpenGL visualizer

Serial Communication• Uses Cserial, free source to implement serial port on

Windows• Have also used POSIX library (termios.h) for possible

expansion to OSX but this library will not compile under Visual Studio for Windows

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FFT Data

iTunes makes FFT data available to visualizer plug-ins while they are displayed

Sent VisualPluginRenderMessage by iTunes at frame rate specified• This message passes a pointer to FFT• 512 linearly spaced frequency steps, 1 byte each,

amplitude only• This is enough information for what we want to do

When sent render message we process the data and transmit as ANSI string (char[9])• [(11)(22)(33)(44)(\0)]

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Zero Cross Detection

Our zero cross detector takes advantage of Atmega168 internal clamping diodes

Keeps voltage on input pins between Vcc+0.5V and Vg-0.5V

Using this we are able to connect N terminal to our ground and L to an input pin, produces 5V square wave

Circuit uses series 1Meg resistors on each pin. This will limit current to diode spec of 1mA max up to 1000V

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Hardware: Triac BTA20-700CW Snubberless

Triacs allow switching of an AC signal• Triggered by the Arduino and

zero-cross detection Phase Control possible

(dimming)• Integral/area under curve

proportional to current through load

Sensitive Gate Triggering (35mA)

Using an opto-isolated triac driver allows for safe and effective handling of power signals

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System Uses 2 Microcontrollers

Microcontroller responsible for light dimming must handle 120 interrupts per second and then trigger lights with precise timing

Handling so many interrupts caused problems with serial communication

Solution was to divide up tasks:• First Arduino waits for serial data from computer, sets

pin to signal second Arduino that data is available• Second Arduino checks “data available” pin when it has

time, after handling light dimming and before next interrupt

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Arduino 1

Waits for incoming data on serial port Parses incoming string stores as 4, 6-bit values

(only 6 pins per port available on arduino) Communicates with second arduino using (2) 6-

bit parallel ports and 2 control pins• Control Pin 1 -> Data Available, tells arduino 2 that data

is ready• Control Pin 2 -> Send next byte, received from arduino

2 to signal next available message

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Arduino 2 Receives input from first

Arduino on parallel ports, convert to 6-bit input to timing value from look-up table

Performs zero cross detection for triac timing• Internal clamping diodes

combined with external resistors reduce 120VAC to 5VDC square wave

• Trigger interrupts on rising and falling edges

Send trigger signals at proper times for light dimming

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Critically Timed Loop

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EagleCAD Schematics

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Design Considerations

EagleCAD schematic almost complete• Need to model DC power supply and off-board

connectors

120VAC lines will be on inner layer of board to minimize trace spacing• Dielectric constant of PCB material is much higher than

that of air• Also reduces risk of shock

120VAC trace width must be about 3mm to reduce resistance and heat buildup.

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Summary

Demonstration

Comments / Questions?