Sunday, 17 April 2011

Light harp for Brighton Fringe Festival 8th May

As part of the Brighton Fringe Festival, BuildBrighton have been invited to take over the Ocean Rooms on Sunday 8th May 2011. We're creating a number of sound- and light- installations for an evening of eletronic music madness.

Of course, the most visually impressive light-to-sound instrument for electroncia is Jean Michel Jarre's Laser Harp. There are quite a few homemade harps around (on Youtube and the like) but even the cheap ones are relatively expensive. The problem is, to get a visible laser beam, you need lots of smoke and something substantially more powerful than a laser pointer off eBay!

I looked into getting a powerful 250mW+ laser and using a galvo to draw the vertical "strings" for the harp - if you look closely on some of the YouTube videos, you can see that this seems to be the current approach as some strings appear to have a bit of flicker (the flicker isn't noticeable when played live, it's just the way digital cameras pick up fast-moving images).

Something like this Light Harp would be very impressive to make too - I love the idea of using some really old retro radio cabinet to house such a cool, futuristic instrument. Using lights instead of lasers also makes it much safer to use in a public space (and encourage the audience to have a go themselves). It plays like a real harp too - with the user "plucking" the light beams to trigger a sound.

The photos and schematics show that a lot of work went into this particular instrument - and the build cost was around $500, a little bit too much for many people to have a got at. In short, it's an amazing instrument, but too expensive and too complicated to try to explain at a single-night event.
What we need is something a little simpler.

Almost all homemade laser harps use some form of LDR (light dependent resistor) and a break-beam sensor to detect when a user has placed their hand over a light source. The laser beam hits an LDR, making the internal resistance low. When a hand breaks the beam, the resistance of the LDR increases and the controller recognises that the user has placed their hand in the beam.
Lasers have a nice, concentrated beam and are relatively easy to work with. LEDs and other diffused light sources are not quite so simple - light can come from a number of sources to strike the LDR, not necessarily from an LED placed over it.

While searching the 'net for "pinhole" lenses (to see if it is possible to narrow a beam from an LED) I came across someone who had a similar idea; only to turn the problem on it's head. Instead of trying to detect reflected (or broken) beams of light, Peter uses a series of light dependent resistors and a pin hole to create "cones" of detection, basically checking for the presence of shadows, as you wave your hand over the instrument.
It's a brilliantly simple but effective idea.

I think it's a project that we should be able to get up and working in a couple of days - and simple enough to create kits for other users to make their own, ready for a "big band ensemble" for the Fringe Festival!