Laser Harp


The laser harp was born as a remake of an old project. The basic idea is to create a variation of a classic instrument such as the harp using current electronic technologies, such as microcontrollers, sensors and speakers.

The structure is made of wood. It has the shape of a rectangle of 96x47x6 cm. On the longer sides there are two separate circuits: on one there are six lasers in a row aligned with the six photoresistors placed on the opposite side.

Lasers (in series) are powered by a 4.5 V battery. The circuit that regulates the photoresistors is a bit more complicated: each photoresistor is connected to an analog input pin on an Arduino.

Arduino powers this circuit and controls the sound output through the program loaded on the board. The program performs a 􏰄rst evaluation of the light intensity detected by the photoresistors and sets the red laser light as standard. Once this is done, every time the laser beam is interrupted, an input pin detects a voltage change and the arduino calls a music shield library function to play the note associated with the speci􏰄c photoresistor.

Having fun creating music, in a new and captivating way, is the purpose of this project. Our team wanted to amaze viewers by playing something cool and fascinating such as a harp without real and tangible strings.


Materials for the structure:

  • wood
  • paint for decoration
  • speakers

For the laser circuit:

  • six laser
  • copper tape
  • 4.5V battery
  • switch (to turn on the circuit)

For the photoresistor circuit:

  • six photoresistor
  • six 10kΩ resistance
  • arduino and breadboard
  • music Shield for Arduino
  • cables and wires

Step 1: Building the Structure

Start with getting material for the structure: we use poplar wood of di􏰅erent thickness in base of the part of the construction. Thicker for supporting parts, thinner panels to cover both circuits.

The size of the structure does not in􏰆uence the functioning of the project, so be creative!

However great care must be taken to ensure that the lasers are pointed directly at the photoresistors. When drilling the 6 holes for the lasers and 6 holes for the sensors, they must be perfectly aligned and located at opposite sides of the structure. It is critical that the laser beams must reach each photoresistor.

Again, our team decided to put laser beams in a row, you could try di􏰅erent positions. However the laser-sensor duality has to be always maintained.

Make a hole for the switch.
Once you have built your structure, with holes for lasers and sensors, you can proceed with the laser circuit.

Step 2: Laser Circuit

Use the copper tape to create 2 long strips that have to pass near every laser hole. One will be the positive strip and one will be the negative.

Now insert lasers in the hole (do not glue them to the structure yet, you will have to do a manual alignment later). Solder the positive cable of every laser to the positive copper strip , and the negative cable to the negative strip.

Prepare the switch: make sure to have wires long enough to solder the switch to the positive terminal of the 4.5 V battery and to the positive copper strip.

Insert the switch in its hole and solder the negative terminal to the negative copper strip.
Turn on the switch and test if lasers turn on. If they do not check all the links between all the components.

Now carefully aim every laser beam to make sure they get through the corresponding photoresistor hole. When the laser is in a good position, glue it to the structure.

Step 3: Photoresistors Circuit

Composing the photoresistors circuit is the most complex step.You will need 6 sensors, Arduino (with the music shield plugged on top of it), a breadboard, six 1kΩ resistances, wires and cables.

Find a good position for the Arduino and the breadboard in the structure: this will allow you to take measurements for wires. Calculate the distance between photoresistor holes and Arduino board and extend pins of each photoresistor by soldering cables.

Now, following the Tinkercad image of the circuit, connect all the components and place the Arduino board and the breadboard in the intended location.

Download the program here (, and upload it into the Arduino board.

Step 4: Putting All Together

For the last step: connect the speaker to the AUX port, turn the lasers on and then power up the Arduino. Wait until the speaker makes a sound: that is a signal for the end of the calibration.
Now you are ready to play Laser Harp.