On Tue, Dec 20, 2005 at 03:02:21PM -0000, Joe McCauley wrote:
> With many of these laser pointers, the metal case of the laser module itself
> is connected to the positive supply. I used a bunch of Alpec units in a
> project last year & had to run them with a -3 Volt supply because the mounts
> they were to be put into were at PSU ground.

!!! Thanks for the heads up! Looks like the case will be plastic then.
I'm lucky I can easilly isolate it electrically.

> These cheap laser units will often die if the supply is shorted out. I'm not
> sure why this is, it may be transients on the supply when the short is taken
> off? They do seem to be quite sensitive to the supply voltage. The diode
> itself is powered from a current regulated by feed back fron a photo diode
> inside the laser. With cheap units like these, designed to be run from
> batteries, you can be sure that the current regulator circuit is not over
> engineered.

Definetely. I've read through Sam's Laser FAQ on the subject, aparently
most of the cheap laser pointer's except the battery to do most of the
current regulation. The laser diodes are then engineered to tolerate a
fairly wide range of currents/voltages compared to standard diodes.
Very, very cheap indeed.

-- 
pete@petertodd.ca http://www.petertodd.ca
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