My first red laser diode emits light!

Thx to all the guides from this forum, i managed to assemble my own DDL circuit on a breadboard and harvested my first dvd-rw LD .
Unfortunately, I couldnt figure out how to remove it from the mount, so now my LD is still stuck in this iron-material-like chamber.

On my first try, I had to turn my pot to the minimum setting to see any light at all. Is this supposed to happen? I measured the voltage accross the LD to be roughly 1.7+V before it started emitting light. And the amount I get is just a wee bit of unfocused light.

From what I understand from the LM317T datasheet, the chip in current regulator mode gives out roughly 1.25V/(R+Rpot). I measured that to be about 7ohms fixed, and my pot at 7ohms minimum gives a maximum current of ~90mA?

Does this mean my LD is dead, or is it working, but I just need to give it more juice?

Also, issit just me, or does the diode not fully discharge the capacitor? I read someone's suggestion to put a tiny resistor accross the capacitor to help completely discharge it. Is this necessary?

Things for me to do now:
Get a 1ohm resistor to help me measure current.
Try to remove the LD from the mount.
Get smaller resistors to put in series with the pot. (What is a good resistance value to try?)

what speed was the burner? mine runs at 420mA ;D ;D and it was a 20x i think. it's an open can.

burners usually need about 3v I think and about 200mA but don't do anything until one of the guru's of the forum come

Mines a Dw1670: "The BenQ DW1670 supports 5x DVD-RAM, 16x DVD±R, 8x/6x DVD+RW/DVD-RW"

I suppose that means its a 16x?

Yeah I thought it should run at about 3V too, found it weird when the meter read 1.7+V...

Not too sure if its open/close can. Can't get it out of the damned chamber its stuck into, and too afraid of destroying my only LD to try harder

Put 7.2 volts into it at should improve things. Keep an eye on the temperature of the LD though

Actually im using a 240V to 9V adaptor to supply my board at the moment. Is 9V too much?

Tested the LD again, I need to increase the voltage accross the LD from the start of 1.6V to about 1.8V before it starts lighting up

Protonoid said:

Actually im using a 240V to 9V adaptor to supply my board at the moment. Is 9V too much?

Tested the LD again, I need to increase the voltage accross the LD from the start of 1.6V to about 1.8V before it starts lighting up

Click to expand...

The diode needs 3V

Peace,
dave

Yep I thought I should need 3V accross the LD for it to work properly, but I've already turned the pot all the way to the lowest setting

Im gonna need smaller resistors to get the voltage higher?

Also, I noted that most ppl on the forum are using batteries to power their lasers. Does my using of a mains power AC-DC adaptor make any difference?

Protonoid said:

Yep I thought I should need 3V accross the LD for it to work properly, but I've already turned the pot all the way to the lowest setting  
Im gonna need smaller resistors to get the voltage higher?
Also, I noted that most ppl on the forum are using batteries to power their lasers. Does my using of a mains power AC-DC adaptor make any difference?

Click to expand...

As long as your driver does good regulation, you are fine. You just need to protect the diode from current/voltage spikes.

Peace,
dave

the reason why u arent seeing 3 volts on the meter is because its not recieving enouche current

try running at atleast 150 mA + u should see the voltage increasing to
limiting the current wil cause the voltage to drop to depending on how mutch current the diode needs / uses

OIC. Thanks guys.
Going down to the shop to get smaller resistors tmr!

Do you know about "Test Loads"? They help you set a safe level of current without tweaking the pot. Basically 4 diodes in series will behave like a red diode, so if you measure the current through them it will be similar. What I had was have a 9V DC socket and run it into my breadboard, from where I attatched it to a LM317 driver. Don't repeat my mistake - I was using solid wire from the adaptor, and it was springy. One time I unplugged it, and let the wire go trailing. It happened to trail right onto the heatsink of the 317, briefly touching it. Luckily the diode was safe, then soon after I repeated exactly the same mistake! Incredibly it survived 1.3A or so at 9V, not once but twice. I think they're more robust, electrically at least, then most people would think.

Sorry for double posting but to add to your comments about resistors: for safety, yes you put a resistor in parallel with the diode but don't worry about it, as long as you are VERY careful about discharging it manually. The best thing to do is have a relay, opened by the main power, that automatically shorts it out when closed. Unfortunately that's not really a space-efficient solution and creates some problems if you wire it incorrectly. With mains adaptors make sure you have a big capacitor. For battery powering, all you need is anything about 2V over the laser diode's drain, as the LM317 uses some power. Lastly, if you want to burn things, which I assume you will want to, you will need to cut it out of its housing, and push it into a body + lens. Don't worry too much about it, as long as you're careful you're unlikely to break it.

Thanks for the tips Charlie!

Went down to the shops today and bought a bunch of stuff including 1ohm resistors and 4 diodes to make a test load.

Was randomly walking around when I found a shop selling diodes for SGD$5! They had 2 different models, but no idea about the specifications. Would it be possible to guestimate their specs if I posted pics of them?

Ther other thing to check on the 9v/mains adaptor is how many ma does it supply?
Rule of thumb I would look for 2 X the output current to the LD.

Regards rog8811

Im using a 12V now, and it can do 1000mA at 12V, which should be fine.

I posted a pic of the dvd mount I opened up.

Im currently testing the top one. That is the LD i want right?

the diode marked in your screen, in the bigger circle, looks to be an IR diode. the other one is the one you are looking for, the red one. As a 16x burner, I would not go over 250mA.