Laser Harp: Construction and concepts

[GoolGaul]

Hey all,

I am new to the PL forum, but I am happy to see that there are so many people with such a wide base of knowledge here.

I want to build a Laser Harp. however, I want to bridge the gap between MIDI keyboards and Laser Harp, specifically addressing missing things like MIDI Velocity (and the reverse; Release Velocity), Portamento, pitch bend, and maybe some other modulations.

Hopefully, we all can get closer to a more expressive instrument.

Anyone who has met with success in Laser Harp Construction, please chime in, your input will surely be of great value.
Anyone looking for a more flexible instrument, chime in too. What would you like to see in the future?

[Stoney3K]

If you want to get started on construction for a laser harp, here's some good pointers.

First of all, you need to make a few decisions. What kind of laser will you be using? Will it use static beams or a single scanning fan of beams? Each has its own advantages and disadvantages.

Implementing velocity and other effects (like aftertouch) is going to be a challenge. The attack/release velocity is dependent on the speed of your hand striking the beam. Using 2 beams is possible, given enough spacing between them, you can extract the velocity by determining the timing between the 2 strikes or releases.

Keep in mind that, in that case, you will need a 2-axis scanning system with a higher scan rate, to project 2 arrays of beams spaced just behind each other.

There's some approaches you can take to detection. For outdoor performances, if the laser is powerful enough, you can use a single photodiode facing up to pick up the reflected light from your hand. Aftertouch can then be extracted from the reflection's intensity (this is the way Jarre's harp works as well), but it requires a carefully calibrated photodiode along with very limited ambient light.

Detecting indoors is much easier. Since there will be a point where your beam terminates at the stage ceiling, you can place an array of photodiodes there and again look at the timing. This can also be combined with bounce mirrors, like in Jarre's first model (in The Concerts in China) or Albert De Jonge's design, since most mirrors will leak a certain amount of light to the other side of the mirror.

As alternative methods, you can look at a detection glove which breaks the laser beam directly, or determining your hand's position with a webcam. (Succesfully demonstrated by Rune Forshaug)

With regards to things like pitch bend and portamento (and possible other effects), most of these are continuous controllers which are usually operated by separate wheels, knobs or faders on your keyboard. I don't see a reason why those can't be added to a laser harp, but that would mean adding more lasers into the mix. It would be a good chance to vary on the design and make it a little different, for example, more 3D.

[GoolGaul]

Hey Stoney,

I was thinking of scanning fan. I want to be able to use multiple scales and tunings.

as for the 2 sets of fans, I was thinking of using green as the main and red as the secondary. In the box, I would combine them slightly offset, so that at playing height, they would be about an inch apart. and sensed with 2 different filtered WiiMote eyes.

[Jem]

Try doing a search from members such as Steve Hobley, Genesis and CarlB and you'll find loads of info on Laser Harps .

Cheers

Jem

[dnar]

Check out Steve's blog here http://www.stephenhobley.com/blog/la...-midi-control/

He recently added a Wii remote to his harp for positional control.

[GoolGaul]

I have communicated with Steve Hobley. He sold his design - big gratz to him on that- and thus can't divulge too much info about this topic (but I am sure that he will be happy to tell me when I am headed in the wrong direction).
His info on WiiMote interfacing will be helpful though...

I'll look for the other members mentioned...

[Master]

This is really what you need! Check out www.laser-harp.com