Cheap way to modulate 32 laser pointers (on|off)

[John Smith]

Hi all,

I was just browsing through the "goldmine electroncs" (surplus
electronics) catalog when I stumbled across some laser pointers priced at
around $1.50. "I wonder what I could do with a bunch of those?" What if I
made some sort of raster display?

Since the laser pointers are so darn cheap, I can just buy up a bunch of em
and use a single spinning mirror to scan the beams from a vertical stack of
them across a wall.. A raster laser light show. I always wanted to try x:y
spinning vector laser art, but it just seemed so complicated.. Raster
graphics are simple to understand and to create, so here's my question: Is
there a cheap circuit (single IC?) that I can use in conjuction with a
microcontroller to drive/modulate this bank of laser pointers as they scan
across the wall? ON/OFF modulation would be sufficient to produce a simple
2 color display with 32 scan lines.. not sure how many "pixels" one could
create, I think that would be a function of how fast the mirror spins, and
how quickly you can blink the laser pointers (slew rate? modulation
frequency? what would you call that.. Bandwidth?) I'm thinking a
led/photodiode combo to send a pulse to the microcontroller each time the
mirror reflects the LED's light back into the photodiode... The pulse would
tell the microcontroller to begin drawing the scanlines.. The program could
automatically adjust the scanline modulation speed to happen in the time
between 2 pulses, this way the speed of motor doesn't need to be constant.

I'm sure many of you have probably thought about doing something like this
before, I'd love to hear any ideas on what might or won't work.. This really
seems like a fun thing to have in the house, and I hope to start tinkering
with the idea very soon.. (The lasers are "in the mail")

PS - It sure is neat to have a place to talk about stuff like this. Glad
you all are here.

Thanks!

Tommy

 

[Rick]

I'm sure many of you have probably thought about doing something like this
before, I'd love to hear any ideas on what might or won't work.. This really
seems like a fun thing to have in the house, and I hope to start tinkering
with the idea very soon.. (The lasers are "in the mail")

PS - It sure is neat to have a place to talk about stuff like this. Glad
you all are here.

Thanks!

Tommy

Some of the cheap keychain laser pointers I have taken apart drive the diode
(which sometimes isn't even in a metal can!) through just a resistor! If this
is the case, and if the current draw is small (under 10mA or so) then you may
get away with just increasing the series resistance (adding another resistor)
and powering the thing directly from your microcontroller I/O lines. Just don't
exceed the max current for the diode, which is sometimes quite close to the
threshold current for small diodes, unfortunately. This is why more advanced
drivers use light feedback from a photodiode mounted next to the laser diode to
operate the diode at a fixed light output level.

Of course, the 100mW 657nm DVD-R 16x laser diodes I have don't even have a
photodiode, so I just power them from a constant current source. Their
threshold and max current figures are farther apart than smaller
diodes...something like 50mA threshold and 150mA (with heatsinking!) for optical
damage, depending on temp (higher optical output at lower temp). Amazingly, it
is actually usually optical damage to the little coated mirrors on the laser
diode that cause it to fail!

Maybe more info than you wanted to know.


Rick

 

[Scott Stephens]

PS - It sure is neat to have a place to talk about stuff like this. Glad
you all are here.

There is also alt.laser & sci.optics.


--
Scott

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DIY Piezo-Gyro, PCB Drill Bot & More Soon!

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