Testing DDL Circuit with multimeter

[rkcstr]

Ok, let me take this one part at a time...

Well I have an adjustable voltage regulator I bought from Radio Shack. It has a selectable voltage output from 3v to 12v, but the current is fixed at 1amp.

With a voltage regulator, it will set the voltage, but the current setting of 1A is just the maximum output, it's not going to push 1A through whatever is connected.

Individual settings are 3v, 4.5v, 6v, 7.5v, 9v 12v. I used 4.5v since the diode appears to draw 2v + the LM317 comsumes 1.5v = 3.5v

The diodes draw more voltage at higher currents. At 2V it's probably means its underdriven, ie not really lasing, which is probably why it looks really dim. I'm not sure what you mean by the LM317 consuming 1.5V... it has a drop-out voltage around 3V for current regulation. This means that if the input voltage is lower than 3V more than the output voltage (the diode's voltage), it will "drop" out of regulation and not put out the proper current.

What I don't understand is, Why... if im giving more than 120ma to the diode, do I get such a dim light?
is it... the diode has a very small tolerance between what will make it fully laze and burn out?*
is it... something with my circuit?
is it... something with the way im reading my MM?

I don't think it's your circuit or multimeter, I think it's the voltage you're inputting to the LM317.

Another thing I dont really get... Why does my MM have seperate Ma settings for 1.5v and 9v?... Do I need to calculate the difference if I set the MM at 1.5v and the diode draw is reading 2v? Should I be adding 25% because of that?
(When set at 1.5v Ma, I get a readuot of x.xx whereas 9v would always give 0.0x, So obviously 1.5v is the correct range setting)

Separate mA settings for 1.5V and 9V? Are you sure those aren't battery voltage testing ranges? Current is independent of voltage, so the voltage shouldn't matter when measuring, unless your multimeter uses some wierd way of measuring current.

When I start reducing the POT and reach near 0-5% resistance... It will all of a sudden get EXTREMELY bright! I mean night and day difference!!! I was able to light a match in less than a second from 6 inches!

I'm guessing you're not using a series resistor with the pot, just the resistance of the pot to set the current? If that is so, that would explain your findings, because as resistance reaches 0, current output approaches infinity (or it's max output, like a limit in calculus). Like I've said already, use higher input voltage!

but... it's never been a visible beam.

You're not going to, unless there's something in the air (smoke, steam, etc). I've run my open can at 400mA, and you still can't see the beam. As chido said, our eyes aren't nearly as senstive to the 650-670nm (red) of these diodes as they are 532nm (green).

 

[viroy]

Ok I will try upping the voltage and testing again. I'll try to take pictures while I do it

Heres my MM:
thebaerwolf.com/MM/digi1.JPG
thebaerwolf.com/MM/digi2.JPG

 

[viroy]

Ok just got done testing again. got some photos and video this time!
the point at which it goes from very dimm to very bright is 68ma on the MM

Here is everything hooked up and set at the very spot where it goes from very dimm to very bright.
Ma reading:
thebaerwolf.com/MM/1.JPG

Voltage reading:
thebaerwolf.com/MM/2.JPG

Laser intensity without camera flash:
thebaerwolf.com/MM/3.JPG

Here are 2 videos.
The first one i am adjusting from 0-120ma:
thebaerwolf.com/MM/1.MPG

The second one I am toying with the spot that it goes from night to day... i am not making major turns on the POT, its just the sensitivity of the diode to the slight adjustment. as you can see im only adjusting it between 60ma and 80ma.
thebaerwolf.com/MM/2.MPG

 

[chido]

Everything seems to be working fine. I don't see any problems. Diodes do that "night and day" effect, I have a short open can and it won't get bright until I get to about 100mA. (I don't remember exactly)
Now all you have to do is to feed more current to the LD, remember, don't go above 250mA.

 

[viroy]

Awesome, I just finished tuning the driver for this... The pot is at like 99% right now and im reading 3v @ 74ma = 222mw. I let it run for a few mins and the housing got just a tad bit warm but seems good to me!

Lights matches instantly!
thebaerwolf.com/MM/3.MPG

I think the next driver I build, im going to use 3 ohms to get a higher range.
Thanks so much to you guys though, especially you Chido!
[smiley=dankk2.gif]

 

[viroy]

Oh actually I do have one more question.
Do I have to use 7.5v all the time, or can I use a 9v battery?
Will upping the voltage also up the current?

 

[chido]

Awesome, I just finished tuning the driver for this... The pot is at like 99% right now and im reading 3v @ 74ma = 222mw. I let it run for a few mins and the housing got just a tad bit warm but seems good to me.

Whoa there buddy hold on a sec. ;D 74mA is not a lot of current. I don't think you're measuring it right, I saw on the videos you posted before you were setting your DMM to the 1.5v battery setting. Set it to where it says 2000m and measure for current again.

I think the next driver I build, im going to use 3 ohms to get a higher range.

3 ohms would let through 420mA which is way too much for a 16x diode. The driver you're using uses 3 10 ohm resistors which limit the current to 378mA which is still too much. ;D I recommend you get rid of one of the 10 ohm resistors so that you bring the limit down to 250mA. I don't recommend you go beyond that when using a 16x diode.
After you get rid of one of the three resistors, apply power to the circuit and turn the pot to the lowest resistance, (this doesn't matter since the remaining 2 10 ohm resistors will limit the current to 250mA) then measure for current, you should get around 250mA, if the DMM doesn't show around 250 millivolts, then you're measuring wrong.

Oh actually I do have one more question.
Do I have to use 7.5v all the time, or can I use a 9v battery?
Will upping the voltage also up the current?

The current will stay the same unless the input voltage gets below 6v, that's why I said you should try 7.5v, you can power it with 9v but I don't recommend you go beyond that since the LM317 will have to get rid of the remaining voltage as heat. A 9v battery won't last too long since its mAh rating isn't high enough. You have to use either 6 AAs, 6 NIMH rechargeable batteries, 2 CR123 rechargeable batteries, etc. Any kind of batteries that can be added up to go beyond 6v and that have a mAh rating of at least 500 IMO.

 

[viroy]

Hey I made a new avatar with that program, thanks again!!!

 

[viroy]

The driver im using now Is one I assembled just the other day, it has (2) 10 ohm resistors = 5ohm.
I can test that on the 2000m setting if you would like but.... isnt that for voltage? I think it will just give me a 1.

 

[chido]

Hey I made a new avatar with that program, thanks again!!!

You're welcome.

My 1st red burner,
many thanks to
Chido!

Aww, you thanked my under your avatar.

;D

 

[chido]

The driver im using now Is one I assembled just the other day, it has (2) 10 ohm resistors = 5ohm.
I can test that on the 2000m setting if you would like but.... isnt that for voltage? I think it will just give me a 1.

It's equal to 2000mV. It's just that your other measurements don't seem right. :-/ A 16x diode being driven at 74mA won't be able to light matches.
Since you already have 2 10 ohm resistors, then just turn the pot to the lowest resistance, the 2 10 ohm resistors should limit the current to 250mA. Then set the multimeter to the 2000m setting and with rog's method measure the mV, with the pot turned all the way down you should get .250 on your multimeter, or 250.something. I don't know how it will display but it should be around 250.

 

[viroy]

Ok, I just tested it again... I am still getting a reading of 74 on the 1.5v Ma setting. When I turn the DMM to 2000m, I get a solid 1. If I set it to 20, I get 3.04. Im not 100% sure but it seems like the 2000m setting is for reading less than 2v.

Will the LM317 allow me to use a 9v battery with this diode?

 

[viroy]

Hey this looks like a good deal if anyone is interested.
Laser power meters, range is from 0-120mw... $50 with shipping to usa
cgi.ebay.com/120mW-Pre-Calibrated-Laser-Power-Meter-Sensor-Module_W0QQitemZ160235631953QQihZ006QQcategoryZ14954QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[chido]

When you set it to 20 you get 3.04v??? That's definitely not right. The 2000mV setting is the one you should be using, not the 1.5v. Could you post a pic of how you're setting your probes to measure for current?

Like I said, you can use a 9v battery but it will not last a long time because of its mAh rating.

 

[chido]

Hey this looks like a good deal if anyone is interested.
Laser power meters, range is from 0-120mw
cgi.ebay.com/120mW-Pre-Calibrated-Laser-Power-Meter-Sensor-Module_W0QQitemZ160235631953QQihZ006QQcategoryZ14954QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

Those have been tested and proven to be crap.

EDIT: The only meter that dude sells that seems to be good is this one.

 

[viroy]

Heres a diagram of how the DMM is connected.
thebaerwolf.com/MM/circuit.jpg