# A cherry-and-walnut laser harp with a tilt bend and a fog machine

Lasers and photoresistors pluck notes, an accelerometer bends them, and a fog machine makes the beams visible. A Teensy 4.1 runs the whole instrument.

- Category: Hardware (build)
- Made by: [Derrick Thomin (DJ Baja Blast)](https://djbajablast.com/diy/on-building-a-desktop-laser-harp/) on Personal site
- Original: https://djbajablast.com/diy/on-building-a-desktop-laser-harp/
- On Afterware: https://afterware.xyz/p/a-cherry-and-walnut-laser-harp-with-a-tilt-bend-and-a-fog-machine

## Can I build this?

- Difficulty: Advanced
- AI-buildability: 3/5 (The Teensy firmware (Karplus-Strong synth, sensor reading, MIDI) is well suited to AI, but the laser alignment, wiring, wooden frame and fog plumbing are hands-on work.)
- Time: A few weeks
- Cost: $150–300
- Parts: Teensy 4.1, photoresistor, accelerometer, ultrasonic distance sensor, laser diode
- Tools: soldering iron, woodworking tools, laser diode driver

Estimates based on the original write-up. How the AI-buildability score works: https://afterware.xyz/ai-buildability

## Build sheet

- Controller: Teensy 4.1
- Sensing: Photoresistors, accelerometer
- Synthesis: Karplus-Strong
- Frame: Cherry and walnut

## Starter prompt

```
Based on "A cherry-and-walnut laser harp with a tilt bend and a fog machine" on Afterware: https://afterware.xyz/p/a-cherry-and-walnut-laser-harp-with-a-tilt-bend-and-a-fog-machine

Write Teensy 4.1 firmware for a laser harp. Read photoresistors on each beam as analog inputs and map the dip depth and speed to note velocity. Use an accelerometer's tilt axis to bend pitch, and output Karplus-Strong synthesized audio on the onboard DAC plus MIDI notes over USB.
```

## Story

Most laser harps use photodiodes. This one uses photoresistors, so the Teensy reads the slow rise and fall of voltage as a hand crosses the beam. Pluck fast and hard and the note gets louder; pluck slowly and it softens. The velocity comes from the light, not a switch.

The extra inputs are where it gets strange. An accelerometer works as a tilt sensor that bends each note flat or sharp as it sounds, and an ultrasonic distance sensor offers a theremin-style control. An encoder wheel on the side adds a fifth input, and there are jacks for an optional looper pedal and an aux in. A Teensy 4.1 drives the synthesis, currently Karplus-Strong string synthesis, with an onboard speaker and MIDI out. The fog machine is plumbed in, so you can see where the laser strings are.

The frame is cherry and walnut. The write-up and GitHub files are there if you want to build your own.

## Resources

- [Full write-up](https://djbajablast.com/diy/on-building-a-desktop-laser-harp/)
- [GitHub files](https://github.com/derrickthomin/laserharp2)

Tags: laser harp, teensy 4.1, photoresistor, accelerometer, karplus-strong, midi, cherry and walnut

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