A few questions about my build

Hi folks.

While saving up for my first laser (an 800mw green), I've got a few questions.

is there a particalar way the dicros need to face the lasers? I know they have to be roughly 45° to the incoming beams, but is there a "top" and "bottom" side to a dichro (e.g. like a playing card - the dealer would almost always lose if he dealt all the cards face side up in blackjack).

Is it sensible to fit a service mode switch inside the projector? By this I mean a switch that allows one to bypass the ilda input, and feed the lasers a low voltage modulation signal, for alignment. My take on this is the service mode switch, and 3 seperate switches (one for each laser), along with a button that has to be held down to make the selected laser(s) run). This rig would make the laser run at low power for alignment purposes. I would put the service mode switch near a case edge, so when the lid is closed, the switch is pressed back into normal mode by a projection inside the case.

I heard you dont need to connect the DT40W's ground connection, except at the power supply, to pin 25 on the ilda breakout board. Is this correct? I assume this is to avoid ground loops.

I have done most of my research, and picked out the lasers I want, and now know their beam heights, so can get some shims in the right thickness (0.8mm for the kvant red, none for the laserwave green, 2mm for the galvo block, and not sure for the blue as have not got info on the prism corrected 445nm diode). My tallest beam height is 29mm. DT40W's come in at 27mm.

The dichros will have a AR coated side and a side with the dichroic layer.

You'll want the beam to be reflected to hit the dichroic side directly, and the pass-through beam to hit the AR side.

/Thomas

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Originally Posted by dash8brj

Is it sensible to fit a service mode switch inside the projector? By this I mean a switch that allows one to bypass the ilda input, and feed the lasers a low voltage modulation signal, for alignment. My take on this is the service mode switch, and 3 seperate switches (one for each laser), along with a button that has to be held down to make the selected laser(s) run). This rig would make the laser run at low power for alignment purposes. I would put the service mode switch near a case edge, so when the lid is closed, the switch is pressed back into normal mode by a projection inside the case.

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Wouldn't it be easier just to turn it down in the software?

In QS you can go down to 10%. I imagine Livepro or LD probably has finer adjustment.

Just set up a BAM of 10% for the entire output grid - if you know your laser power you now know the output power with the BAM active ie 800mw @ 10% = 80mw - remember as well lasers may perform differently from their stated powers so whatever method you use to attenuate the output you need to check the power with a laser power meter 1st:

Here's one I drew earlier for Zone 1 (if using Beams remember its Zone 8 usually - and also remember to check all patterns to be projected are set to the same zone as the BAM is assigned to):

http://img4.imageshack.us/img4/7352/bamyj.jpg

Beyond that if you wanted to do it via hardwire for extra safety I imagine it would be possible to switch between the normal driver connection and one containing a resistor or tuning pot to take the power down at hardware level. However, electronics at this level are beyond me so I'll leave it to others to describe how it could be done as I don't want to suggest anything that might fry expensive lasers or drivers.

To do it in hardware would be pretty simple too...

A SPDT button on each modulation line. NC connected to ilda input, NO connected to the case switch.

Case switch could be one of these:
http://www.hobbyengineering.com/H1883.html

Other end of case switch connects to a low voltage source - maybe a diode in series with a resistor for 0.6V.

Something like this:
Attachment 23392

/Thomas

Thats the exact idea badpip, and using the microswitch was a good suggestion - the system is ready to use the service mode as soon as the lid comes off. The whole idea is to be able to do farfield alignment should the machine come out of alignment during transport without having to hook up the dac and laptop. The electronics is fairly simple - I was going to use a few silicon diodes in series for voltage dropping and a 10k resistor for current limiting. At around 0.6-1v, the lasers will be at a pretty low power.

Yes i understand lasers behave differently at low power versus full, I guess a shorting switch across the diodes, would solve that problem - tweak at low power, and perform final adjustment at full power (thus only having a full power static beam for a short period).

as for the dichros, how do you tell which side is which?

I would go a step further, and wire a pot as a potential divider between 5V and 0V.. In fact the bereakout board i am working on to go inside my new housings has this, including many other cool features ;)

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Originally Posted by dave

I would go a step further, and wire a pot as a potential divider between 5V and 0V.. In fact the bereakout board i am working on to go inside my new housings has this, including many other cool features ;)

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hi, want to share the "other cool features" ?:)

dave321

There are a few of them, mainly revolving around DMX control to do cool stuff like invert's and add a bit of extra control for multi projector set ups.

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Originally Posted by dave321

hi, want to share the "other cool features" ?:)

dave321

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