Laser Harp Page

Dec 2022/Jan 2023/Feb 2023
Page Under Construction

While visiting Meow Wolf in Santa Fe I saw my first laser musical instrument and had some fun playing around with it. It only had 3 lasers but it was still fun. When I returned from my vacation, the idea of building a more full on laser harp planted itself in my brain. I decided to build one with 12 laser strings and which would have no physical controls but be controlled entirely by a web application. As usual the plan for my laser harp kept expanding and I wanted all of the following features/functions:

Feature	Function
MIDI Operation	I wanted the harp to be a MIDI instrument that could be plugged into any MIDI supporting equipment. The harp doesn't produce any sound on its own, it just generates MIDI codes which cause MIDI sound sources to which it would be connected to produce sound.
Controlled via Web Page	I didn't want to build physical controls into the harp. I wanted the harp to be completely controlled via a web app.
Key Change	The ability of the harp to play in any and every key.
Octave Shift	The ability of the harp to play over a wide octave range
Scale	The ability of the harp to play in many different scales from the basic chromatic scale to more obscure east Asian scales.
Program/Voice	The ability of the harp to use the full 128 programs/voices supported by General MIDI
MIDI Channel	The ability of the harp to send MIDI messages over any MIDI channel (1 .. 16).
String Order	The ability of the harp to reorder the strings so that the lowest note is the left most string or the right most string. In other words, the string order should be able to be set Left to Right or Right to Left.
Volume	The ability of the harp to control its volume.
Modulation	The ability of the harp to control modulation level.
Reverb	The ability of the harp to control reverb level.
Chorus	The ability of the harp to control chorus level.
Portamento Time	The ability of the harp to control glide time between sequential notes (portamento time).

This project is made up of three parts: First, the triangular structure that houses the lasers and the embedded electronics which I made out of hardboard. Second, the electronics that runs the harp software. I wanted the electronics to be as simple as possible and I think I succeeded in that it consists of only a WEMOS D1 Mini ESP32 module, 12 lasers, 12 light dependent resistors (LDR) and miscellaneous resistors. Finally, the software that runs the harp and powers the web app.

At this point the laser harp is not yet finished but here are some pictures taken during its construction.

Picture	Description
	The electronics that drives the laser harp. On the left is the external power jack. The ESP32 module is in the middle. The MIDI DIN connector is on the right. This module will be mounted inside the laser harp. The harp will be externally powered via a 5 volt wall wort.
	Rear view of the electronics. There is a 1.8K resistor for each of the 12 strings and 2 resistors for the MIDI output. Each string will also have a Light Dependent Resistor (LDR) for sensing laser light.
	Point to point wiring was used as can be seen here.
	In preparation for wiring up the harp I attached all of the required wires to the breadboard because once it is installed in the harp I wouldn't be able to solder them.
	The harp is built as a triangle. This image shows the front of the harp before construction was finished and the harp was sanded and painted.
	This is the internal structure of the laser harp. It consists of 2 equilateral triangles with corner blocks of wood for support. Equilateral triangles have equal length sides and 60 degree angles. The cavities created with this arrangement are about 1 1/2" square. Enough room for the internal wiring.
	Here you can see the hole that have been drilled which will each contain a laser that will be pointed at a LDR directly below it.


	Here is the web app web page used to control the laser harp. The harp provides its own WiFi access point called "Laser Harp". To control the laser harp, connect your device to the access point and point your browser to: 192.168.4.1 and you should see this UI. Any change made via this UI is reflected immediately in the laser harp's operation.

Questions and comments to me Craig at: calhjh@gmail.com