On Tue, Dec 20, 2005 at 11:21:10PM +1300, Jinx wrote:
> > > Why not just hack a laser pointer ? Dirt cheap
> > 
> > Oh I would, but this is an art project that I've beeen comissioned
> > to make. So I have a budget of about $100US for the laser module
> > but also I have to think about the long-term maintanance of the
> > project
> 
> Well, far be it from me, but ........ ;-)
> 
> You're making an assumption about what will be available in
> 10 years time. US Lasers could be long gone by then. I daresay
> something else will be available, but according to Sod's Law it
> will be just different enough to be annoying

Definetely one of my worries. I mean, by asking for such modules, what
I'm really thinking is are they commonly available? Because if they are
now, there's a good chance that they'll be available in 10 years, even
if not specifically from US Lasers.

> > Unfortunately that means that potentially unreliable things like
> > hacking a laser pointer are out
> 
> Reliability is the responsibility of the workman !!! ;-)) If you
> build within spec and have a good margin there's no reason
> to think any unit would fail prematurely. And you document
> it yourself so that someone in 10 years time will have no trouble
> fixing it

You're right for sure, but I guess my point is that that $1 laser
pointer you get from a surplus place doesn't *have* specs to follow.

> > It's gotta be off the shelf and documented, so that in 10 years
> > when the laser craps out it'll be easy to replace with another one
> 
> Seriously, what makes "off the shelf" so dependable ? I've had
> my share of garbage OTS, and I'm sure everyone else here has.

As I say above, at least the OTS stuff *has* specs to follow, even if
they lie and the hardware doesn't meet the specs. Makes me look less bad
too!

> If you're considering PWMing the one you get, is that any less
> "hacking" than taking a cheap pointer and doing the same ?

Not if the datasheet mentions PWM and I check it over with one of their
engineers. :)

> I've looked at modules available from RS and their prices are
> way higher than you'd pay at a stationary supplier for basically
> the same thing sold as a pointer. Eventually I got some LM3s
> from Oatley in Australia and they work great
> 
> http://www.oatleyelectronics.com/lasers.html

Thansk for the tip, looks like a decent module, and nice price!

> Oatley also sell lenses (collimating and line, plastic, they're OK)
> 
> I wonder though if 5mW is going to be enough. (I notice Digikey
> describe the 38-1010-ND as "4.8MW" but I'm guessing that
> should be mW !!!). 20mW might be more like it if the display
> starts getting big and the dot has to move around a lot

It's going to be stationary actually. See, what I'm doing is mounting
the laser to the shaft of a stepper motor. Then I *very* slowly pan it
across a wall. Each 12 hour period the laser dot will make one trip from
one side of the wall to the other. The whole assembly is mounted into
the ceiling of a room and some control lines and power is run behind the
wall to a control panel somewhere. The only tricky part is microstepping
the motor for a sufficiently high resolution, I have a 400 step/rev
motor I'm using with 64x microstepping. Actual realised resolution seems
to be maybe 1600steps/rev. 

-- 
pete@petertodd.ca http://www.petertodd.ca
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist