EENG 383 Microcomputers Final Project
Auto Headphones
April 25, 2014; 1:00pm; Colorado School of Mines
Electrical Engineering Department
Taylor Ray
Adriana Johnson
Project Overview
• Design:
o Play/Pause when headphones are taken on/off
o Volume control with two push buttons for volume up and down
o Both done with simulation key presses in Windows Media Player
• Purpose/Goal:
o Studio tool for sound engineers can use this tool
o User friendly- know volume levels and playing/paused at all times
o Saves time and energy
Design
• Overall System
o Arduino Leonardo
o Headphones
• Subsystem One
o IR Receiver
o IR Transmitter
• Subsystem Two
o Two Volume buttons
• Subsystem Three
o LCD Screen
The Arduino Leonardo
• Strengths of Design:
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Simpler coding process over the HCS12 microcontroller
More compact design
Easy hardware compatibility
Uses digital outputs
Can simulate a keyboard
http://arduino.cc/en/Main/arduinoBoardLeonardo
Break Beam Sensor
• IR Receiver TSOP48
• Detects signal, pulls OUT low
(pause)
• IR output:
o Port C7
o Pin 13
o Timer 4
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IR Transmitter
Software based LED
Allows for compact design
Robust Design
Saves on cost
38kHz signal
http://inside.mines.edu/~whoff/courses/EENG383/lab/tsop4838.pdf
http://inside.mines.edu/~whoff/courses/EENG383/lab/tsal6200.pdf
Push Buttons
• Two buttons
o Volume Up
o Volume Down
• State 1: Reads zero volts, when not pushed
• State 2: Reads voltage (across resistor), when pushed
Timing Diagram
• Headphones
• Button press is 20.0 ms
LCD Display
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Liquid Crystal Display (LCD)
Describes: volume, play, and pause
Trimpot for LCD contrast
4 data pins used – save on Arduino
Pins
Timing Diagram
• LCD Screen
Software
• Arduino Leonardo is recognized by computer as a peripheral
device
o Uses USB HID Protocol to send keystrokes, just like a typical keyboard.
• Programmed with Arduino software
• Windows media key presses being simulated
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Play: Ctrl P
Pause: Ctrl P
Volume up: F9
Volume down: F8
Pseudo Code
Setup():
Initialize Pins for input or output
Turn on LCD and Initialize by prompting user to “Place Headphones on head to begin playing”
Set state of headphones to not playing (state = 0)
Initialize volume to reasonable level
Loop():
If IR receiver indicates headphones are on person’s head (from break beam IR sensor)
If state = 1 (playing)
Do nothing
If state = 0 (paused)
Start playing and reinitialize the volume by sending simulated keypress to computer
If IR receiver indicated headphones are not on person’s head (from break beam IR sensor)
If state = 1 (playing)
Pause music by setting state to 0 and sending simulated keypress to computer
If state = 0 (paused)
Do nothing
If Pushbutton_up is pressed
Debouncing software
Send simulated keypress to computer signaling volume up
If Pushbutton_down is pressed
Debouncing software
Send simulated keypress to computer signaling volume down
Display volume level and whether playing or paused on the LCD screen using Arduino LCD Library
Results and the Future
• Overall result:
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The break beam sensor captured when the user took the headphones off or put them on
The pin was pulled low and indicated that headphones were put on
A pressed push button simulates key press to change volume
The LCD relates the actions that are happening
Simple, robust design that is compact enough to fit in headphones
• Could improve design by:
o Internalize cables and break beam sensor
o Add next/previous song
• This would make a great product for Audio Engineers or
general consumers
Comments and Questions