Group 10 proposes designing a laser harp that uses light dependent resistors to detect when laser beams are broken, triggering a MIDI interface to send note and volume information to a synthesizer to produce sound, with an LCD screen to display the note and octave and a keypad to shift octaves. The laser harp would have 12 laser beams to play 7 major notes and 5 semitones in one octave, using a rangefinder sensor to set the volume based on where in the beam the break occurs. A microcontroller would interpret input from the detectors and keypad to send the appropriate MIDI messages for processing by a synthesizer when the laser beams are

1. Group 10
Ben Burbridge
Ryan Maltais
Shane Jonson
Aakash Vasudevan
Eleven Engineering
Client

2.  Goal to take a real harp and replace the steel strings with
laser beams.
 http://www.youtube.com/watch?v=WkkhcwXpYy4
 Conventional Harp type vs. Laser Harp
 Laser Harp speciality
 Based on MIDI

3.  Stands for:
Musical
Instrument
Digital
Interface
 Digital Message used to communicate between electronic
musical instruments
 Can be used to control another music instrument to produce
any note

4.  Enough lasers to play seven major tones and five semitones to
make an octave
 Volume of the note should be determined by where the beam is
broken
 LCD screen to display the last note played
 Keypad to allow user to shift octaves
 Full size harp
 Produce a MIDI message when a laser beam is broken

7.  Light Dependent Resistors (LDRs)
are used as the main light detecting
element
 An Operational Amplifier (Op-Amp) is
used in “comparator mode” to produce
digital signal
 In “idle state” the Op-Amp output is
close to 0 V (logic zero)
 The change in resistance in the LDR
when a beam is broken (“playback
state”) causes the Op-Amp output to
shoot up to 5 V (logic one)
 Circuit replicated for each of the
twelve laser beams

9.  A sensor that outputs an analog voltage
based on the distance of an object from
the sensor
 Used to set the volume level of the note
played on the harp
 Analog voltage read and interpreted by
the XInc2 microcontroller to determine
the volume level of the note
 Volume information sent as MIDI
message to the sound synthesizer

11.  Keypad allows the user to increment
or decrement the octave of the harp
 LCD displays the last note played on
the harp and the current octave of the
harp
 Default Octave is middle octave (4)

13.  Used to shift logic level from 3.3 V to 5 V of the output MIDI message
from XInC2 microcontroller
 Logic level shifted message transmitted to sound synthesizer through
a 5 pin DIN MIDI cable

15.  Interprets signals from detector
network, range finder and keypad
 Determines the note played, the
volume level and the octave from the
i/p subsystems
 Sends MIDI messages as UART
signal at 3.3 V logic level
 Displays the last note played and the
current octave on the LCD

16.  Microcontroller waits for a note
to be played on the harp
 When a note is played, the
flowchart is executed to send
out MIDI messages
 Binary semaphores are used to
“protect” memory from multiple
thread access
 Output MIDI message is logic
level shifted to 5 V by MIDI
Out circuit and transmitted to
sound synthesizer

17. A
B
D

18. Client Specification
 Seven major tones and five
semitones to make an octave
 Volume of the note should be
determined by where the beam
is broken
 LCD screen to display the last
note played
 Keypad allows user to shift
octaves
 Produce a MIDI message when
a laser beam is broken
Project Capability
 12 laser beams for seven major
notes and five sharp notes
 Volume level set for all beams
using a single range finder
 LCD screen displays last note
played as well as current
octave
 Keypad integrated and allows
user to increment/decrement
octave
 Laser harp produces
appropriate MIDI messages
when a laser beam is broken

19.  It can only play one note at a time. Can’t play chords.
(monophonic)
 Rangefinder only changes volume
 The range of notes is only one octave
 The range seen by the range finder.
 Musical effects changed on keyboard. Not harp.
 No demos pre programmed in harp. Done by keyboard

24. Seven Nation
Army
White Stripes