One of my most vivid concert
memories is seeing Jean Michel
Jarre perform in 1986 at the city of
Houston’s 150th birthday celebration.
He played music by breaking laser
beams with his hands. The beams
came out of the stage and went off
into space, and for a long time
I thought it was a fake — I couldn’t
understand how this instrument
could work without any sensors
above. That started me researching
and tinkering, and 22 years later,
I figured it all out and built my own.
Now I have several versions of the laser harp. The
one I perform with uses a powerful laser and a
scanning mirror system, designed for professional
lighting effects, that splits one beam into multiple
beams that can fan out and move dramatically. This
article describes a simpler harp I designed more
recently, which uses inexpensive laser pointers and
doesn’t need the scanner.
Photograph by Jacques De Selliers
The harp works as a MIDI controller, so it doesn’t
make sound itself, but generates a stream of MIDI
data to drive an audio synthesizer. Each beam
strikes a photocell, and when the player’s hand
interrupts it, the sensor prompts an Arduino
microcontroller to send a MIDI “Note On” message.
Additionally, a range sensor reads the position of
the hand, which spawns MIDI controller messages
that change the sound’s qualities.
First I’ll show how to make a single-beam laser
theremin, which changes pitch with the position
of your hand. Then we’ll replicate the circuit and
reprogram the Arduino to produce a multi-string
harp, with each beam corresponding to a different
note. The Arduino has 6 analog inputs, so this harp
is limited to 6 beams, but at the end of the article
I’ll suggest ways to expand it.
MATERIALS
Arduino board I used an Arduino Diecimila, available
from the Maker Shed ( makershed.com) and
SparkFun ( sparkfun.com). Also consider the
breadboard-pluggable Boarduino from Adafruit
Technologies ( adafruit.com).
Laser pointers ( 6) any color, but they need to have
a decent IR filter to avoid confusing the range
sensor. I bought 25 red pointers from eBay, where
prices go as low as $1 each. Green is more visible
and thus scores a higher coolness factor.
DC power source, switched, 8V–12V, 2–3 amps
I used an old 8.5V camcorder charger.
Adjustable voltage regulator Trossen Robotics
#P-VR-DE-SWADJ, trossenrobotics.com
7805 voltage regulator, 5V from RadioShack
LM324 quad op-amp chips ( 2) RadioShack #276-1711
Red LEDs ( 6) I used a 10-LED bar array, Jameco
#1553686 ( jameco.com).
Resistors, ¼-watt: 220Ω, 1.5kΩ ( 6), 3.9kΩ ( 6),
68kΩ, 1MΩ ( 6)
Capacitors: 0.1μF ( 3) and 300μF tantalum ( 6)
Photocell, 100m W ( 6) Jameco #202403
Sharp GP2D12 or GP2D120 IR range sensors ( 6)
from Trossen Robotics
Tumbled rocks, translucent ( 6) craft or bead store
Potentiometer, 100kΩ from RadioShack
5-pin DIN (MIDI) connector from RadioShack
Blank circuit boards I used 1 dual mini and 1 medium,
RadioShack #276-148 and #276-168.
24-gauge hookup wire various colors
Heat-shrink tubing
8-pin headers ( 5) (optional)
Aluminum tubes, ½" × 36" ( 2)
Wood and screws I used ½" fiberboard
Black paint
TOOLS
NOTE: I’ve developed my projects on a PC, so the
software tools I use are PC-based, but there are
equivalent tools for the Mac and Unix/Linux.
Computer
MIDI utility software to test output. I recommend
MIDI-OX ( midiox.com).
Software synthesizer I recommend Superwave P8
( home.btconnect.com/christopherg/main.htm).
USB-MIDI interface such as M-Audio Uno
Soldering equipment and solder
Insulated wire various colors
Wire cutters and strippers
Multimeter
Alligator leads ( 2)
Saw
Drill
Vise and clamps
Stephen Hobley, a photographer by trade, wants to continue tinkering with electronic instruments, but lately his
brand-new role as “Dad” seems to take up most of his time.
Make: 65
