Laser Harp I

Affordable and pretty simple to build framed laser harp using cheap laser pointer modules and a Teensy 3.2

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Framed laser harp with up to 16 beams, MIDI over both USB and 5-pin DIN, adjustable octave and transposition, plus a whole bunch of selectable scales. Estimated cost less than €50.

Objective was to build a simple and cheap, but useable, laser harp. I consider it a prototype/base for future builds, so I'm calling it the Laser Harp I. At the same time it probably is a good start for anyone else wanting to build a laser harp, so just go ahead and build one if you feel like it.

The harp is based on cheap laser modules (up to 16 red laser diode modules, <5mW). Makes it pretty safe, but you still should not look directly into the beams, of course. I take no responsibility here. Don't be stupid. Don't let kids play with it unattended and so on.

To control settings like sensitivity (adjust to ambient lighting), scale, octave and transposition (start note), there are four potentiometers, plus a switch to divide the scale settings in two banks. For testing or a more simple build, these can be left out if you just comment out some code accordingly. Default settings are set in the variable definitions.

The start note (leftmost beam) is set to midi note number 60 (middle C). From there you can adjust start octave from -4 to +3. As the transposition setting goes from -12 to +12 semitones, you will in total get a very wide range. In some cases it will even go outside the midi range. Those notes will then be silent.

Scale settings available are:

Upper bank

natural minor/aeolian
melodic minor
harmonic minor
major blues
minor blues
major pentatonic
minor pentatonic

Lower bank

combi diminish
raga bhairav
raga gamansrama
raga todi
bali pelog

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  • 1

    Prepare your frame of choice. A non conductive frame material like wood or plastic is required. Wood is probably the best choice (no risk for melting when we solder). Holes for lasers and photoresistors should be measured and aligned with care to get nice and even parallel beams. Make the holes for the photoresistors small enough to keep the component body from going through, and wide enough to allow the legs through, even with some shrink tubing on to prevent shorting. I believe I used a 3.5mm drill. Holes for lasers should be wide enough to allow for some adjustment.

  • 2

    On both sides of the row of holes, stick 5mm copper tape strips along the entire length of the bar. Do this on the top side of the LDR sensor bar (top) and the bottom side of the laser bar (bottom). This will be the power bus for each bar.

  • 3

    Put laser modules in place and solder all positive leads to one copper tape strip via a current limiting resistor, and all the negative leads directly to the other copper tape strip. For the laser modules used, the voltage and current needs to be right. With a 5V power supply and 4.5V 20mA lasers, a 27 ohm resistor in series with each laser will do the trick. Make sure your power supply can manage the total current draw. In this case, the lasers will draw 320mA combined. For other laser modules, just do the math for what resistors to use, or use an online calculator.

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gareth wrote 17 hours ago point

Hej Johan

Nice project - I've wanted a laser harp since Jarre played Rendezvous Houston..!

My Teensy arrived yesterday so just getting my toolchain sorted.

Looking forward to the update for chords/keyboard update as I think this will make it easier to play. Please post a schematic update when you have one ready.

Could you also recommend a (simple!) PC-based synth to use for testing?


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Johan Berglund wrote 6 hours ago point

Hej Gareth,

Thanks! Jarre has been a big inspiration for me too in this. I've watched him play his laser harp live in concert a number of times. It never fails to impress :)

I've made a preliminary schematic for the keyboard version and fixed some errors in the code. Will upload to Github when I get home in a couple of hours.

I'm an Apple person myself, so I don't really have much knowledge in PC synthesizers. For my testing, I've been using Thor on the iPad and nLog midi synthesizer on the iPhone. Also some kind of midi monitor software can be helpful if you want to troubleshoot, experiment or develop further.


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jeffw wrote 2 days ago point

Great project.  Were there any libraries/#includes needed to run for example MIDI suite of functions on Teensy? Any chance to add velocity, aftertouch parameters?

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Johan Berglund wrote a day ago point

Thank you! I did choose the Teensy for the no frills usb midi. No #includes needed, as teensyduino takes care of everything. You just select Teensy 3.2 and USB Type "MIDI" in the Tools menu of the Arduino IDE. Also, I used no libraries for the DIN MIDI either. 

If you want velocity, you could monitor the rate of value changes from each sensor. I didn't see much benefit for my intended use, so I kept it simple. Also aftertouch using sensors for distance or other stuff should not be too hard to implement.
You could even add built in audio output using the teensy audio library with not too much hassle. I left the A14/DAC pin unused for this. Myself, I prefer using external synths, so I didn't bother about that. For now at least.

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