Troubles getting my first laser build off the ground

[Fractle]

Hey Guys!

I've been trying to get my first laser set up; it’s a 5mw 650nm diode with a DDL driver. I've been reading around for what best to do,
The diodes came from Aixiz. I got them mostly because they were cheap and I could practice soldering on them once I got the driver going.
5mw 650nm laser diode 5 pack, AixiZ

I got the driver from here and I'm going with this circuit. the fixed resistor value is 68 ohms in parallel and I have 4 AA's (6.4V!) for a power source.
Laser driver - It can be done

I also built the test load that's described towards the bottom, this one consisting of 3 1N4001's (~2.1V drop for this build) and a 1 ohm resistor. I hooked those two things up and was able to measure the current running across the 1ohm resistor, which was in the 21-25mA range. It should be within tolerance! After soldering some wires to diodes (and it not working) I got a test socket from Aixiz to try.
Laser Diode Testing Socket TO-18, AixiZ

I've tested it with an LED (is that a valid test?) just to make sure the wiring wasn't screwed somewhere, and stuck an LED in the top (+) and left (-) socket holes to make sure it worked too. Even with the laser diode in the socket I get.... nothing! No lights or anything. This stuff is all on a breadboard too.

I thought that there might be some ESD issues so I got a grounding wrist strap, still a no go. At this point I think it’s probably something stupid that I'm missing. I'm relatively new to electronics. Even if I burn it out there should be some kind of optical output? Could it be emitting in IR?

I'm at a bit of a loss, please help!

 

[Spectre Gadget]

It could be the tester socket not making good contact. Whenever I'm tuning a driver or setting up a laser I solder all the points. A loose connection could kill a diode.

Did you make sure that you shorted out the output of the driver before hookup and/or after energizing the circuit? If the cap is left charged it could easily fry a diode.

Also, check to make sure you have sufficient voltage to forward bias your diode. That spec sheet says 2.2VDC for operation. I'm only saying this based on the chart you have attached. It says 7.2VDC, while you're supplying 6.4. On the same subject, if your testing your batteries with a multimeter out of circuit, you will get a higher reading because the batteries are not under load.

If you did fry a diode, it should at least make some slight glow.

 

[Flaminpyro]

I agree with the low voltage, with this DDL circuit you are running at the min voltage and may not have enough for the LD.

And shorting the output before you hook a LD to it is very important !

If you can not get it going your option is to buy a ready made driver and go from there.

 

[Fractle]

Hey guys, thanks for the replies!

Last night I upped the power supply, I had a 9v that read as around 7.1V so it seemed ideal, but I still got nothing. thats what makes me thing I'm doing something obviously wrong since I get no light from diodes no matter how much power I pump into them.

So Specter, you're saying that the issue might be that these things are on a breadboard, not soldered together? Its true that sometimes I have pieces that need to be reseated on the breadboard, and its not the sturdiest construction. I had bought a P3 driver and had a similar problem when I tried to bread board it up with a diode, the warning light would come on. I didn't think that would be a big issue.

I think I'll take flaminpyro's advice and get some preassembled drivers and some modules (not diodes) so I can rule some things out more effectively. I don't think I'm asking the right questions yet lol

Also, is there an easier build to start out with other than the 5mw 650nm diode? its small and takes small current, I didn't know if something with more heft would be easier to get going.

 

[Spectre Gadget]

Well, don't get ahead of yourself. I harvested a many 5mW or so diodes before I bought my first one. Let's just say I've seen a few dead diodes! Thankfully little red diodes are free.

Now, when you said 9V battery I'm hoping you don't mean the square battery with the two buttons on top? Those batteries are glorified stacked coin cells making 9VDC, yet little to no current. If they're reading 7VDC that battery is deader than a hunk of volcanic rock. If all you have is common alkaline cells (1.5VDC, AA, C, D, etc.) stack about 5 of them in series. I don't know what part of the world you're in, but if you have a hardware store nearby like Home Depot, they sell lithium flashlight cells. Get two CR123's and hook 'em up. Lase away.

As for your circuit, it could work. If your breadboard is brand new, clean, and still holds things tight then it might work. BUT, since you're saying you've had problems before I would toss it. Another option would be some prototype board. The holes in the board have pads you can solder your component to, and then a wire. No more finicky connections. I've seen people here even cut down prototype board small enough for a medium-sized host.

You also mentioned IR earlier. You shouldn't need to worry about that with these diodes. I think there are some out there that do emit both frequencies, but they typically have 4 pins.

BTW, is this a labby setup or is this going into a host?

 

[Fractle]

Hey guys,

To answer some of your questions, yes specter, I was using a typical 9v battery, and yeah it seems pretty dead. I'll have to pick up some $2 laser pointers and get some more diodes lol.

I took your advice and soldered the driver and the diode all together. When i turned it on I could read a very small voltage across the two diode pins, something like 9mV. When I turned my pot I was able to make it go up to 11. My first thought here was that there wasn't enough juice coming in, so I tried to recreate that measurement! unfortunately I didn't solder the pot on very well, so it skipped that part of the circut and I was able to read a little less than 6V (the power supply is 4AA measured at around 6.5V). the diode is probably dead. BUT!! this is the first time I've been able to read voltage across the diode, in every attempt prior to this I was getting nothing at all.

Is it normal to be able to read voltage across the diode pins? It also sounds like you're right, I need more power!

PS: at the time of my last post, i did not realize that a module was a fully set up laser. ^_^
your response makes a lot more sense Specter, lol.

 

[Spectre Gadget]

Is it normal to be able to read voltage across the diode pins? It also sounds like you're right, I need more power!

I would avoid reading across the diode. These little guys are very sensitive! I would hook up to your test load, and verify your driver is still working. You should be getting at least 3VDC out, if you have enough battery power.

9-11mV is definitely not enough to drive a diode, and if you're supplying the 7.2 VDC needed, you should definitely have more than that on the output.

 

[Fractle]

Yeah I need to throw another AA into the mix.

the driver's probably broken, its bypassing the pot and resistors entirely so that'll need to be fixed....

Is there a way to read the voltage (or some other reading) when the diode is connected and running? maybe if I hooked up the meter leads to wire before it gets to the diode?

Also, I probably know the answer, but with a diode that needs 2.2V running it over 5V is going to keep it from ever lasing again right? Would it still be possible to get a faint glow at the right power readings? I'd still consider that progress!!!!

Hell, getting a meter reading across the diode is kinda progress...

Thanks for all the help!

 

[Spectre Gadget]

Sorry I've been AFK for a while. Dang flu shot was rough this year...

Is there a way to read the voltage (or some other reading) when the diode is connected and running?

I'm afraid not. The best bet is to read the voltage across your heavy resistor in your dummy load, laser diode out of circuit and put away. Trust me, I have a red I'd like to crank up but I need an LPM first, or disassemble the laser completely.

...maybe if I hooked up the meter leads to wire before it gets to the diode?

The problem is that any little slight variance in current could destroy that diode. They are super sensitive components, unlike LEDs.

Also, I probably know the answer, but with a diode that needs 2.2V running it over 5V is going to keep it from ever lasing again right?

These diodes are like LEDs in that current is more important than the voltage. Yes, you can blow it with too much voltage, but most likely that voltage caused the current to go way beyond what it's designed.

In detail, almost every solid state component out there (LEDs, LDs, diodes, transistors, etc.) needs a certain amount of voltage to overcome before it operates. This is called forward bias. Once it operates, it acts as a switch.

For example: You have 3 LEDs. They have an operating voltage of 3.4V. Hook these 3 LEDs to a car battery (12V). They light because the battery has sufficient voltage to forward bias the LEDs (0.7V x3 = 2.1V btw). All seems fine, except the LEDs get hot and blow. Why? Because solid state devices will act like a short once they are forward biased. They will pass as much current as they possibly can, unless the current is regulated.

*Slap* Ok... back to your answer. It depends on the diode and what current it can handle. This also explains why your circuit wasn't working with the other battery configurations. Not enough power (voltage and resulting current) to run the driver, forward bias the laser diode, and supply enough current to regulate your diode.

Would it still be possible to get a faint glow at the right power readings? I'd still consider that progress!!!!

Yes and no. A diode could fail on the die, resulting in faint radiation. It could also have it's supply wires burned in two, cutting the circuit. Then, you will see nothing. The only way to know for sure is remove the diode, and replace with that dummy load and take some readings.

Hell, getting a meter reading across the diode is kinda progress...

Your multimeter will either put a very slight load on the circuit, or send voltages when measuring for current, either way killing the diode. You may get lucky once, but these things are really sensitive to this kind of stuff.

 

[Fractle]

Thanks Gadget! this was actually reeeeaaaly informative. :beer:
As a side note, what would 0 Bias be? I know that the P3 driver has a 0 bias pot along with a voltage and current one.

I added an additional battery but got pretty much the same results, leading me to believe the diode is toast, and now I'm all out of diodes.

I'm new the whole electronics thing, and I think it might be a poor choice to choose one of the most complex things right out of the gate. there are too many unknowns here. My circut could be wrong, but I don't know if I damaged the diode when I soldered it up. I think I'm going to start with something simpler, maybe a premade driver and a diode that's meant for it.

What are your thoughts on this? I know its cheap Chinese crap, but at least I could practice soldering cheap diodes onto cheap drivers!
Power Supply Driver for 5mW 650nm 660nm Red Laser Diode LD | eBay

Is there a better way to learn than this? I know you mentioned Harvesting diodes out of pointers, is there a good place/thread to go to learn about that? I need a couple of wins on this somewhere lol

Thanks again for all your help!

 

[jwwilson23]

i thought you could measure the current w/ a lm317 driver (or other linears)
and a fully charged 9v battery will work..but you wont get full power, you should see at least some light. could be another problem. how about you just get a couple 9v batteries and put them on? (in parallel)

 

[Spectre Gadget]

i thought you could measure the current w/ a lm317 driver (or other linears)

Perhaps so, depending on driver, but I'm assuming a completely fubar'd diode. To prevent any doubts I think the test load would be the best route, IMO.

how about you just get a couple 9v batteries and put them on?

Only if in parallel. 18VDC might be too inefficient for the circuit, sucking away even more of that tiny bit of power in the form of waste heat. Even then we're dealing with really low demand batteries.

If you're setting this thing up outside of a flashlight host, why not just find a 6V power brick and hook the output of that to your driver? That way you have the voltage, current, and you don't have to worry about holding terminals on batteries. (I'm assuming that's the appeal with 9V batteries.)

 

[jwwilson23]

Perhaps so, depending on driver, but I'm assuming a completely fubar'd diode. To prevent any doubts I think the test load would be the best route, IMO.



Only if in parallel. 18VDC might be too inefficient for the circuit, sucking away even more of that tiny bit of power in the form of waste heat. Even then we're dealing with really low demand batteries.

If you're setting this thing up outside of a flashlight host, why not just find a 6V power brick and hook the output of that to your driver? That way you have the voltage, current, and you don't have to worry about holding terminals on batteries. (I'm assuming that's the appeal with 9V batteries.)

yea forgot to mention in parallel (oops )

i think i saw that bionicbadger said you could use multimeter w/ linears and he is reputable so if he or any other person more reputable than us can answer this that would be great!

and i dont think the 9v batts are actually 9v, but your option suggested sounds good.

And to the OP it seems that the battery isnt too much of the problem because your diode should at least put out a little light.

:beer: Justin