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ArcticMyst Security by Avery

Troubleshooting my first laser attempt

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I'm new to lasers, but have pretty much experience with electronics and homemade circuits. I actually use the LM317 to make some custom power supplies, so I already had the parts I need for the DDL driver.

I salvaged an 0811 diode from a broken HD-DVD player, and bought a glass lens from eBay. I can't get the diode to lase even when I have the pot at its lowest resistance. I've tried a homemade 7.2V pack as well as a 9v battery, and I still get the same thing. The circuit works fine when I use LEDs with it.

Any ideas?
 





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john_lawson said:
was the diode the broken part of the hd drive?


I'm pretty sure it wasn't. The front plate had been snapped off and some of the inputs were ruined, but the inside and the drive itself looked fine.
 
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You have the polarity correct on the diode? Have you verified with a mulitmeter your driver is working properly?
 
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pseudolobster said:
You have the polarity correct on the diode?  Have you verified with a mulitmeter your driver is working properly?

Yeah, as long as it has the same polarity as a DVD burner's diode. I watched the voltage go up and down on the meter when I varied the resistance. I was using an LED at the time and its brightness was changing as I did this. . I haven't tested the current, though.
 
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Bionic-Badger said:
You're using the correct pins right?

Looks like I had it wrong, it's lighting up now. Thanks!

What's the highest constant current I can supply to this and how do I do so? My meter (GreenLee DM-60) has current settings for 10A, 200ma, 20ma, 2m, and 200 microamps. I assume I'd connect it between the positive lead and the diode and use the 200ma setting?
 
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An 0811 isn't as powerful as an 803t, though you should be able to give it 80 or so mA.

And yes, you're correct on how you'd measure it.. it needs to go in series with the circuit, bridging the gap between the driver and diode.

Another way to do this is to put a 1ohm resistor in series with the circuit and you can check the voltage in mV across the resistor, according to ohm's law the mV = mA @1ohm. This is a little more accurate since a lot of multimeters have lousy current measurement.

Congrats though, that's a great feeling when you first get to see that eerie purple color and you know you did everything right, isn't it?
 
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I don't have a 1 ohm resistor handy, so I'm using a 10 ohm. I can just divide the reading by ten, right?

I wasn't getting a reading when using the 200mv setting, but I do when I have it on 2v. Would this still be accurate?


Yeah, it was pretty awesome to see it light up for the first time! It's strange how it'll reflect as violet or blue depending on the surface.
 
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I connected the meter with it on the 2v setting, and I get a reading of .27v when the diode starts to lase. This is with the 10 ohm resistor instead of the 1 ohm. Does this sound right? If so, then I guess this is 27mv (.27v/10) that I'm getting.
 
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Zom-B said:
27ma sounds about right.

Great, thanks!

I got it up to 40ma/mv with the pot at its lowest resistance (0.5 ohms) and the two 10 ohm resistors in parallel. I removed the resistors and tried only the pot, and I got up to 50ma/mv at lowest resistance. What can I change to get this to go up to 80 or 90ma? Would the 10 ohm resistor that I'm using to measure the current be sapping some of the power?
 

IgorT

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The 10 ohm resistor, on which you're measuring the current (by measuring the voltage drop, right?), does not affect the current, but it does introduce a voltage drop, that changes with the current, and means that your driver requires a higher input voltage, than it would, without that resistor. Still, if you give the driver enough voltage, the resistor will not affect the current.


But with 7.2V you were simply at too low voltage. 7.2V is good for reds.. I don't know the exact Vf of the 0811 diode, but the PHR needs >5V, almost 6V by itself, depending on the current. The 317 needs 3V on top of that, so 9V is really the bare minimum - 9V is the voltage your battery should have when empty. When full it should have more, so that the driver can keep your current constant over the entire battery voltage range.

Still it should work at least at the start.. Is your 9V battery full? Measure it's voltage under load.

In any case, you need three Li-Ions for it to work for any real amount of time.


Then you need to set the pot to the MAX resistance FIRST, because then the current actually will be what you set it to, and kill your diode, as the driver jumps into regulation. Right now it's not regulating, which is why you can't set the current properly. At the moment, your driver is set to 2.5A (0.5 ohm) theoretically. Not that it can deliver that much, especially not from a 9V battery.


Set the pot to max resistance and give the driver what it needs, then adjust again. The 6V mentioned in the tutorial is the minimum for red diodes, not for blu.

And the two 10 ohm resistors in parallel mean, your max current is limited to just under 250mA, which is too much. Use only one 10 ohm, and your max current will be slightly under 125mA, which at least won't kill your diode instantly,  if you don't set the pot right.


The reason it works with a LED is because of it's much lower voltage requirements, compared to a blu diode. There, the driver gets enough voltage on top of what the LED needs, to regulate the current.
 
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Thanks, your explanation was incredibly clear!

I hooked a new 9v to it, and I get up 92ma out of it with 10 ohms of resistance. I imagine it would go a little farther (up to 125ma) once I get my three 10440 batteries. I guess there's not enough of a history with the 0811 to know exactly what its limits are. I wonder how long it would last at 125ma if I had a decent heatsink.
 

IgorT

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Well. i guess it's possible a DT0811 has a higher Vf..

What you could do is, simply measure the voltage across it, when there is 92mA flowing through it. Then measure the voltage of the battery under load.

The 317 needs 3V, so 9V should be enough at least for a short time.. Unless the Vf is above 6V! :eek:
 
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I finished my laser and I have some photos here:
 

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