[sdiy] Laser Harp in action

[Richard Wentk]

At 09:26 29/06/2004 +0100, Oakley Sound wrote:

> > Where did you get it, and how much was it?
>
>Its a standard 'big show' laser available from one of the big stage
>lighting companies. I'll ask Martin where he got it from, but be
>prepared to spend some cash. I think it cost in the region of 1000UKP
>including the power supply that comes with it. The galvo with its
>electronics is a standard Catweazle laser scanner at around 600UKP.

Hmmm. 1000UKP for 650mW is *cheap*. Very cheap. You can pay a lot more than 
that for a lot less power. If that's what you paid I definitely want to 
know where you got it from.

I've seen people quoting 12,000UKP for a 50mW DMX show system. That was up 
at the silly end, but it does put it into perspective.

One other question - does your model include analogue or TTL brightness 
control, or is it just a fixed brightness output?

>If you want to use this live you have to ensure that the laser can't go
>off on its own. You can't just set it up and power it up. The laser
>housing has to conform to UK laws and it took Martin a while to make
>sure all these were carried out. Its as safe as any big venue laser
>projector can be.

Okay, I've been round this one, with all the literature from H&S and 
various EU departments and everything. :-)

> > I wasn't sure if the laser harp really triggered notes, or if it was
>just a stage prop.
>
>Rumour has that Jarre does have problems with his later harps. False
>triggering and a very visible low scaning rate.

Building a laser harp with 80s technology was one *hell* of a thing, and 
I'm very impressed anyone got the idea to work at all.

It's a bit easier today, and with today's galvos there's really no excuse 
for a slow scan rate.

If you have brightness mod you could avoid false triggering by overlaying 
some kind of modulation signal that's different for each beam. Then instead 
of a binary yes/no check for backscattered light, you could see if the 
light synced with the source mod to have better confidence about which beam 
was being played.

This would be mono only, obviously, but given that most people only have 
two hands I don't think that's a major drawback. :-)

>I can't confirm the former though and we would love to hear different. But 
>remember this is
>the guy who apparently plays chords on his minimoog in live shows....

Or uses a 'keyboard' that lights up but doesn't do much else. ;-)

Richard