[sdiy] Laser Harp in action

[Oakley Sound]

> Do the beams really need that much power?

No. The first one we used had 60mW. But the 650mW one is used so that it
can be seen from a long way off. There were plans to use this one
outside.

> can the player use it to light a cigarette?

Almost certainly... so long you have a long cigarette and tie your hair
back. :-)

> Did you get it up to 650mW in the end?

Yes. This is the really bright green one. Its very hot as a direct beam,
but once it is fanned over the eight beams, the power in each beam is
considerably less. When the harp is first turned on, we have the one
beam directly up. A VCA driven by a simple RC network slowly opens up
the fan. Impressive, very impressive (but you are not a Jedi knight yet)

The laser is moved by a mirror that can be moved in an XY plane. The Y
plane is fixed for this application.

> 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.

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.

> Not to be the doting mother here, but shouldn't you be wearing
protective eyeware?

Every time the thing went on, we had a procedure where we all check for
shiny things and where we are looking. That said, when the laser is on
in a clean air enviroment you cannot see the beams directly. You have to
be very careful. But this is true when you are working with any
dangerous machinery or voltages.

> Do you have any details on the optic and sensor parts of the harp?

This is one area I would like to spend more time on if only for me being
a geeky perfectionist. But the sensor is a standard PIN diode daylight
sensor from Farnell. With a 650mW laser getting enough light back into
the sensor isn't a major headache. :-) The sensor is housed within a odd
looking dish shaped reflector to increase and focus the area of light
pick up. We also have a background sensor too. This picks up the ambient
light and provides the threshold from which the other sensor will have
to overcome to trigger the sounds. In the 650mW case, the background
sensor was superfluous.

> 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. 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....
OK, maybe he's had it fitted with a midi scanning keyboard, but maybe
not. Shame if so, because he's always been a bit of a hero of mine.
(Until he did Revolutions.. oh dear oh dear)

Regards,

Tony Allgood                         www.oakleysound.co.uk

Oakley Modular Synthesisers      Penrith, Cumbria, England