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[on:]

Got a cool project running. But each unit needs 5 laser diodes, or perhaps good-ol-LEDs.

I can buy laser pointer cat toys at the local megamart for under $4.00 each. So I was shocked and awed when I went to try to go from scrap-parts-prototype to something produceable and I found that laser diodes at Digikey, etc. are >$4.00 per each, and laser "modules" go for >$25.00 per each.

Maybe I'm asking for too much of a good thing. Don't know that I need a laser. What I need is
  * the capability to project a narrow beam so that I get about a 1cm wide spot at 3 meters ... this is good.
  * A 4mm spot at 3m distance would be all that and gravy.
  * Any visible color (no IR).
  * Intensity under 5mW ... If a human at the device can see that 1cm spot on a white wall 3m away it's bright enough.
  * It doesn't even have to be a round dot. If the beam is slightly fan shaped it is OK. 10cm by 0.5cm at 3m?

Ideas out there? Low cost laser diodes? Narrow beam LED with a lens? (I'd hoped to avoid optics but price may override pleasure.)

kBit

[Reply #1 on:]

You can get laser modules cheaper on ebay drop-shipped from china; but you'll still be looking at about $4 or 5.00 per module (actually, here's 8 for $25.00 - http://goo.gl/qD7uU). What you're seeing though @ digikey vs cat-toys is volume manufacturing/purchasing; I am sure if you bought 100,000 modules, they would only likely cost $1.00 or less each. Also - you don't want bare-diodes, unless you plan to build your own driver to control the current (not too difficult, but then you have to source those parts and build the circuit, etc). As far as LEDs (with or without optics), if you can find them in a narrow beam and are ok with the optics side of things (and if you can source the optics cheaply), then it may be an option - once again, ebay is your friend (actually, if you really want to manufacture things, you start to look into the various chinese wholesaler search engines and places like Asian Sources and such - and buy in humongous bulk - to get the really good deals).

[Reply #2 on:]

Dealextreme has these laser modules:

http://s.dealextreme.com/search/laser+module

going from 1.54 including shipping.

I've ordered lots of stuff from them, just takes a while to arrive.

[Reply #3 on:]

$1.54 would certainly be in the acceptable range. Is dealextreme a closeout house? If this goes anywhere I'll need a source that isn't end of life. Might be making them for a few years.

Where can I find more about the driver needs? Why is a laser diode so much fussier than a standard diode?

I do recall the lensmaker's equation from college physics so maybe I need to find a source for small plastic lenses and use $0.15 red LEDs.

[Reply #4 on:]

You're going to need a lot of LEDs and lenses to get to the point that you can cook toast with them.

[Reply #5 on:]

I'll need a source that isn't end of life.

That is why you pay the price at Digikey

a source for small plastic lenses and use $0.15 red LEDs.

I think you might struggle at that.

Why is a laser diode so much fussier than a standard diode?

From http://www.repairfaq.org/sam/laserdps.htm

The following four possibilities exist for the laser diode drivers inside laser pointers. (Unless otherwise noted, this applies to red laser pointers, not the DPSS green types with their high power laser diode pump requirements.)

    Series resistor: There is no active regulator. A resistor limits current to a safe value with a fresh set of batteries. The laser diode is driven like an LED. As the batteries are drained, current decreases proportional to the difference between the battery voltage and the diode drop (about 2 V) divided by the resistances. Since output power and thus brightness would also decline dramatically with battery use, this approach is only found in the cheapest of laser pointers. See the section: Laser Pointer with a Resistor for a Regulator.

    Constant current: Laser diode current is set to a safe value between threshold and maximum. This takes care of battery voltage variations but still would have problems with changes in the laser diode output with temperature. This is rarely, if ever, found on red laser pointers but is used for green laser pointers since the high power pump diodes for the DPSS laser module do not have or need optical feedback for adequate regulation.

    Optical feedback - unregulated reference: Some laser diode drivers use the monitor photodiode to control laser diode current but do not have constant voltage source like a zener diode circuit to use as a reference. This is fairly safe for the laser diode as long as the correct battery types are used. For these, output brightness will vary somewhat with battery voltage and will thus decline as the batteries are drained.

    Optical feedback - regulated reference: The best designs (and all those using IC driver chips) will maintain nearly constant output power until the batteries are nearly exhausted.

[Reply #6 on:]

Well I wouldn't design a commercial product around dealextreme parts. But for hobby use / first prototype it's ok.
You never know if it goes out of stock and if it comes back again with them.

[Reply #7 on:]

@Grumpy_Mike
I think you might struggle at that.

Do you think that no one makes small lenses? I have drawers full. I was hoping to avoid multiple parts, possibly requiring manual calibration to keep manufacturing costs low.

*or*

You do not think that LEDs can be purchased for $0.15?

I see right now standard LEDs @ Digikey less than $0.06 each in qty 3000. Sorry that the Queens coin isn't as valuable.

Series resistor: There is no active regulator. A resistor limits current to a safe value with a fresh set of batteries

Thanks for the info.

The laser is no sweat then ... no more complicated than any standard LED. Set the value to limit the current based on the supply bus. I was worried that perhaps there was some big non-linearity such as with some gas tubes that I had not accounted for using the cat toy devices in the prototype. But given the cost differential using an LED vs a laser diode I think the laser version is going to the circular file and v2.0 will use LEDs and lenses.

[Reply #8 on:]

@wortelsoft
Yes, if you go back to the second sentence of my second paragraph of the original post, I'm trying to put together a produceable design.

I have built proof of concept prototypes based on $4 laser pointers (ugly project box, cat toys, battery holder home-made circuit board for a parts cost of less than $40 -- $20 of that being the cat toy lasers) and now I want to find a way to put 5 narrow beam light sources, a couple batteries, circuit board, and a power switch in a neat (professional) looking box about the size of a cigarette pack for $15-$25 (less is even better) parts cost for a run of 500 to 750 units. There is a strong possibility of doing a second run of 1000 to 2000 units summer 2012.

[Reply #9 on:]

tmart has these laser modules:

you can buy some you need from very cheap price,eg:blue laser pointer and laser pointer more and more