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Hey kids.....

C

Clive Mitchell

Jan 1, 1970
0
Hey kids... Let's take a laser to bits.

It doesn't seem that long since a club laser was typically an argon unit
with a water cooled head. Now with DPSS greens and surprisingly high
power "normal" red lasers the cost of a scanning club laser has crashed
to very affordable levels.

I just bought a three colour unit (red, yellow and green) on ebay with a
stepper based scanning system and really like it. Print out this
picture and I'll talk you through what's inside....

http://www.emanator.demon.co.uk/laser.jpg

OK. The green laser is the large black extruded aluminium chunk at the
front left. It's rated 50mW but because green lasers use a much higher
power infra red diode to stimulate a crystal to lase in a different
wavelength, then double it's output frequency with another crystal the
power dissipation tends to be pretty high compared to a conventional red
laser diode. Despite being half the optical power of the red laser the
green outshines it in perceived intensity due to the spectral response
of the human eye. It's very bright indeed.

The red laser is the surprisingly small brass tube clamped in an
aluminium bracket just to the back right of the green lasers black
extruded case. For 100mW it's tiny! But then the construction of a red
laser is very simple compared to other types.

The beams are combined by the 45 degree piece of dichroic glass mounted
on the short pillar in front of the red laser which passes the green
beam straight through but reflects the red beam sideways so that it is
in parallel with the green beam. The assembly is accurately positioned
so the two beams combine to produce a good bright yellow when both are
active.

The beams then pass on to the deflection system which is very simple in
that it uses two small stepper motors to wiggle two bits of front
mirrored glass. The stepper motors are high resolution, but the actual
movement is small so everything "drawn" by the laser has a slightly
stepped appearance with the mechanical mass of the rotors causing
"loopy" edges. At power-up the motors get their positional reference in
the same way as many moving mirror lights by winding round and stalling
against two protruding screws that have been "fine tuned" by being bent!
:)

At the back of the unit is a transformer for the fan, steppers and
control card, while the lasers themselves are surprisingly controlled by
two independent mains powered switch mode supplies stacked on top of
each other. The switch mode supplies are at the middle left of the case
with the cream coloured PCBs. Each of the laser supplies has a simple
two wire logic level control from the main controller.

The main control PCB (the green one) has a bit of basic power supply
circuitry on it and a large processor which looks as though it might be
an Atmel, although there is a label covering the chip data. The
controller has 10 channel DMX and localised control options with a built
in microphone and sensitivity control. The stepper motors are
surprisingly controlled by a pair of ULN2803 octal Darlington arrays
with the circuits paired into four 1A drivers per chip. I suppose it's
an easy way of driving the steppers and has the nice benefit of
integrated diodes for shunting any inductive backlash from the windings.

And that's about it. The images projected onto a wall show the rough
output from the stepping motors, but when the beams are cutting through
the haze it looks great. The price difference between the stepper
version and the full galvanic (high resolution) deflection system is
huge so it's a small price to pay for a good visual effect.

In short quite a fun unit. Perfect for clubs or just as a techno-toy.

The unit dissected in today's class was the EL-150RGY bought from:-

http://stores.ebay.com/Laserworld-Shop

Right. What can I take to bits next. :)
 
A

Andrew Gabriel

Jan 1, 1970
0
The unit dissected in today's class was the EL-150RGY bought from:-

Very interesting Clive.

What sort of input can it take?
For example, could I feed it a set of vector coordinates and
beam on/off commands from a computer so as to write some text,
like you might with a full vector scan display?
My guess is the steppers wouldn't be fast enough to maintain
any kind of static display with many vector elements in it.
 
C

Clive Mitchell

Jan 1, 1970
0
Andrew Gabriel said:
Very interesting Clive.

What sort of input can it take?
For example, could I feed it a set of vector coordinates and beam
on/off commands from a computer so as to write some text, like you
might with a full vector scan display? My guess is the steppers
wouldn't be fast enough to maintain any kind of static display with
many vector elements in it.

It couldn't handle text, but their faster systems can do handwriting
fonts. The DMX control is strictly pattern selection, colour and
position.
 
C

Clive Mitchell

Jan 1, 1970
0
In message said:
does the DPSS green have a peltier cooler on the pump diode, or is the
heat control done with just a heat sink?

Purely heatsink. There's no sign of any wiring for a peltier device. I
suppose higher power modules might benefit from one, but this DPSS
module is only 50mW so the large heatsink should be OK. The units seem
to carry a good guarantee.


There's a fairly good airflow through the case. Unfortunately it also
blows past the front silvered mirrors, but there is advice on cleaning
them in the manual.
 
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