[Cyborg] 200 laser diodes

Mitch Altman maltman23 at hotmail.com
Sat Jun 5 17:51:02 UTC 2010

> Date: Sat, 5 Jun 2010 10:12:48 -0700
> From: mrericboyd at yahoo.com
> To: adi at hexapodia.org
> CC: cyborg at lists.noisebridge.net
> Subject: Re: [Cyborg] 200 laser diodes
> I'd love to help make that testing rig.
> It'd be especially interesting if we could test the unit-to-unit 
> variation in optical output. We wouldn't need a rig capable of 
> measuring absolute power, just one capable of monitoring relative power 
> between exposures. I'm thinking any old photo diode should be able to 
> do that, yes? Just hook up the laser & a photo diode to an arduino, do 
> a brief pulse of light, record the reading, do the next one, etc... The 
> hard part might be the laser-diode alignment, we probably need to build 
> a mechanical rig of some sort. We could also monitor the electrical 
> power consumption, I wonder if these lasers vary much in efficiency.


As long as the photo diode can see OK enough at the wavelength of the light from the laser diodes we ordered, we can get relative output.  But how do we measure absolute power output?  If we have one light source of known output, then relative will be OK when matched against it.  Anyone have a light source with known output?

> I'd be pretty upset if there are more than a couple of duds in this lot; 
> I think 5% would be outrageous. At any rate, it's too late to tack on 
> more now :-(. What makes you think the failure rate will be so high? I 
> am wishing I'd ordered a couple extra dozen - I didn't mostly because I 
> didn't want to get stuck with more than my 16.


In ordering parts, I have never received any that didn't work.  And I order a lot of parts.  My guess is that they either all work fine, or hardly any do, 'cause we got ripped off.  And it seems unlikely that we got ripped off.  My guess is that all of the laser diodes will work (though with a large variance in light output).  But, of course, you never know.

> I have an interesting safety question: do you think that PWM controlling 
> the lasers would actually make them eye safe? For instance, let's say 
> we discover that the true optical power of the lasers is something like 
> 10mW. Would it actually make them any eye safer to PWM control a laser 
> to 50% duty cycle? Theoretically that reduces the "power" to 5mW, but I 
> expect that in practice it's the peak intensity on your fovea that 
> causes the damage, and PWM will not reduce the peak intensity. Thoughts?


PWM definitely can reduce the effective light output.  But, will these laser diodes pulse at a high enough frequency to allow for PWM?  We'll just have to try and see.









> On 6/4/10 1:48 PM, Andy Isaacson wrote:
> > I wouldn't bet on the order getting here in a hurry, but that's OK with
> > me. :)
> >
> > By my math it works out to $2.65 per diode, so I get 18 for a total of
> > 47.60. But we should probably assume that 5% of the order will be duds,
> > so maybe we should tack on a bit to cover losses. Thoughts?
> >
> > Maybe we should build a test rig to test out the shipment? I'd be down
> > for helping with build and testing if anyone else wants to participate.
> >
> > -andy
> >
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