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Thread: Alternative drive for Chinese 'Lambdapro' DPSS heads?

  1. #1
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    Default Alternative drive for Chinese 'Lambdapro' DPSS heads?

    Does anyone have details of pinouts on the connectors for Lambdapro heads? I have two, one 100mW, the other unknown, but larger, like their later more powerful ones, but with the older PSU and a narrower beam than is usual for their later ones. I suspect that the TTL modulation is purely a driver box related thing, and that a completely different driver, TEC control, etc, can be built. Complete with analog proportional modulation. And that maybe someone's already done it.

    I'd settle for just knowing what each pin in the plug is for so that I can run these at much lower powers. They both have really nice beams, and I'd like to run them at low powers with lifetimes that might then exceed my own. Can anyone help me to do this? I could buy a cheap low power head but that would be cheating. And running a high power device at low power is usually a better way to get long life. I'd like to get tens of thousands of low power hours if I can.

  2. #2
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    Not an answer to my own post, but I did come up with this, which might be of use to someone here:

    Investigation for power control in the Lambdapro LPS-100 supply for UG DPSS lasers: Find the track joining R43, C10, and pin 2 of U4, close to and likely associated with pot RwI. 3.3V on the other end of R43 (100K) charges C10 (unknown, but small disk ceramic), whose voltage is read by U4. This is the soft start circuit. The supply side of R43 also rises moderately slowly at power-up, and may change during operation. Without knowing more about this voltage's origins, it is best to copy it rather than replace it as a basis for modification.

    Suggestion for power control:
    Find the 5V supply and ground, prepare a small PCB with an op-amp as voltage follower, and room for a 1K single-turn preset pot, or pads to wire a chassis mounted pot. Open the supply side of R43, take its source to feed the voltage follower, and wire the pot from the op-amp's output to ground, and connect the open end of R43 to its wiper. This will allow power change without defeating the soft start mechanism. Stable power is another matter, because the diode will put out a lot less heat, wavelength will shift too, so it may be best to leave all the other controls set, knowing that at full power the laser will work as intended, and at low power for long life, just set the pot wherever it gets wanted results.

    If instead of a voltage follower, a differential amplifier is used, it may be possible to do analog modulation even with Lambdapro DPSS lasers with only TTL input, but the results will not be great, and there is a risk of putting the voltage on the output above 3.3V with possibly disastrous results. But if like me you want your old Lambdapro laser living out its long last years like a lava lamp put out to grass, this is the way to do it. And that was more than enough silly alliteration with the letter L from me. But that laser diode should pretty much live forever and the beam should still be a very nice TEM00. And if you crank the pot to full it should work at full power as well as it ever did.

    Zoof did a modification for power control, but looking at his LPS-100 picture (Google will still find it, on Picassa, I think), it was done differently. In an old PL post he said he'd not got the notes for that, so here at least is some way to do it.

    EDIT: Fast analog modulation would have to do this differently, perhaps by replacing R43's 100K with something low enough to allow fast speed, but all bets are off. For a start, goodbye soft start if you do this...
    Last edited by The_Doctor; 09-06-2013 at 16:46.

  3. #3
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    I cant see how its worth wasting any time on a 100mw chi green
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  4. #4
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    Well, this is why I speak of lava lamps. If there was ever a candidate for relaxen und watchen das blinkenlights, this is it. I can set this up now and shine it at a wall 24-7 and not worry about whether I'm doing the wrong thing with it. Damn fine air pollution monitor, as it happens.

  5. #5
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    Hey Dave, this might interest you. Now that I have that dimmer working, I set up the green HeNe that Jem sold me, beside it, and matched brightness. And for clean TEM00 beam with good Gaussian profile, low divergence, and lack of spill, the Chinese DPSS wins easily. And the HeNe is damn good. There is also a strong plane polarisation there, and at low power (up to maybe 50mW) the output is clean, stable, quiet. I'm pretty certain that people will pay good money to get specs like those...

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