Hey kids.....

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. :)

--
Clive Mitchell
http://www.bigclive.com
.

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