A-to-D Record Player
Microcomputer Architecture and Interfacing
Final Project – Spring 2014
Ross Bunker
Jade Irizarry-Swordy
Concept
Inspired by a small digital music box, we wanted to design
something better.
Our goal:
Create a music playing device with the same basic mechanical
features of a record player, but with digital inputs
The Journey of a Signal,
from Analog to Digital
Sheet Music
Using black and white markings on paper, we created binaryencoded sheet music.
-- 6 bits
-- 64 total possible
notes or chords
Sample ‘Paper Record’ :
How do we read the sheet
music?
Reflective Optical Encoders
A device that couples a light-emitting diode
to a light dependent resistor
Sensor Array
Building an array of reflective optical encoders, we are able to
read our sheet music:
Sensor Schematic
We have a digital value,
now what?
Digital Value
Notes
0
A
1
A#
2
B
3
C
.
.
.
.
.
.
Sensor Pseudocode
Set up {
Initialize pins A0 through A5 for input, and 3 pins for speaker output
Notes [ 37] = { 2 octaves of notes }
Chords[ 37 – 64] = { popular chords }
}
Loop {
Find decimal value of binary sensor value;
If (note value < 37 )
Play single note;
3 identical frequencies speaker output pins;
If( note value >37 )
Play chord;
3 different frequencies, each on its own speaker output pin;
}
Arduino Tone Library
Outputs varying-frequency PWM signals
--Allows us to begin playing notes and stop playing
notes
Playing a Note
versus Playing a Chord
Arduino allows us to create PWM signals that mimic any
frequency
To create a chord, we simply tie together three notes
Playing a single note….
A#
A#
A#
Playing a whole chord….
C
D#
G
Timing Diagram
General Overview of
Reading Music
1. Sensor Array detects black and white
2. Black and white converted to binary
3. Binary converted to decimal
4. Decimal used to look up a note or chord
5. Note or chord outputted to speaker by creating
PWM at desired frequency/ frequencies
But wait, how do we read
all those notes along the
spiral?
Tone Arm Control
What is it?
Our method of lengthening the amount of music
How?
A small circuit at the end of the photo array tracked a black marker
Tone Arm Control Input
A black tracking line will be added around the outside of the
data track on the sheet music
A pair of photoresistors, or light-dependent resistors (LDR),
will be used to track the black line
Voltage on AI0 and AI1 will
differ, depending on the
location of each relative to
the tracking line
Tone Arm Control
Considerations
How do we track the black line without oscillation?
The difference between the two voltages must be compared
to a threshold constant to prevent oscillatory feedback!
Tone Arm Control Input
Position of Tracking Sensors relative to Input Array
Tone Arm Control Input
Differential Sensor Measurement has not exceeded threshold
Tone Arm Control Input
Differential sensor measurement exceeds threshold
Tone Arm Control Output
Physical position of Tone Arm is controlled by a servo
Why a servo?
Absolute position is always known
Small and controlled angular adjustments
Tone Arm Pseudocode
If difference between sensor voltage 1 and 2 exceeds defined
threshold
Add increment to current output frequency
Else, if difference between sensor voltage 2 and 1 exceeds
defined threshold
Subtract increment from current output frequency
Tone Arm Timing Diagram
Okay, but won’t the sheet
music just be sitting
there?
Platter Motor Control
Obviously the sheet music needs to spin for this to work!
33 or 45 RPM will need to be slowed down to accommodate
our sheet music
Done with analog components rather than Arduino control
Platter Motor Control
Schematic
Runs off 13.6V supply built into the record player
Voltage divider from potentiometer
used to control MOSFET gate
A system of pulleys was also
necessary to reduce the operating
speed further
Platter Motor Control Pulley
System
Conclusion
Sensor reads record, communicate via Arduino
Motor spins platter at reasonable speed, using pulley system
Tone arm depends on circuit inputs, controlled through
Arduino
Questions?