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Old 04-15-2008, 10:02 PM #1
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Default homemade driver questions

Well I rigged up your standard do it yourself driver on a breadboard with parts identical to the one in the video from Phazonx in that other post. Another diagram I found elsewhere recommended a 4ohm resistor and his recommended two 10's in parallel for a 5 ohm resistance so I just went with dual 10s cuz I couldn't find a 4 :P So I turned the 25 ohm potentiometer down to absolute maximum resistance. I tested it and it's 25.0 ohms exactly and on minimum, it's basically 0 ohms. I'm using 4 brand new D batteries that measured at 6.51V total and as I turn it up and down, the output voltage stays steady at 5.90V. From minimum to maximum on the pot I get an output of 4 and around 220 milliamps. So it seems to working properly. Now just to make sure, the laser diode I'm testing with is a 650nm 5mw one that specifically says run it at 3.2V. So sending 5.9 volts normally would fry it but since I'm limiting the current, it won't fry and it's all good, right?
Well here's the "problem." The instructions in the video say to turn the pot all the way down and then connect the LD then connect the power source. Then you're supposed to turn the pot up until the diode starts emitting light. Well my diode turns on even at maximum resistance and it looked pretty bright too. According to my earlier measurement it's only sending 4 milliamps under those conditions. The kinda sketchy stats on mfgcn say operating current is 40ma. So it's seriously running on 4? Is that normal? In fact I pulled one of the 10 ohm resistors so it was double the resistance at 10 ohms and that only brought it down to 3 ma and it still ran the LD. What's up with that?
So assuming it can run on extremely low current, that runs into another problem. When turned all the way up, it sends 220ma which is probably enough to fry the 5 mw LD. But eventually I'm swapping out the diode with a 200+ mw laser diode from a 20x DVD burner. First of all, will that one turn on with just 4 millamps too? And second, if I want that sucker to pop a balloon and such, I'll need it running near max power, right? So I have to turn it up manually until it's near it's max operating current. So that brings us to the big question: how many millamps should a DVD burner diode safely run at?


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Old 04-15-2008, 10:21 PM #2
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Default Re: homemade driver questions

Ok first, you can't just connect your DMM probes directly to the wires coming from the dirver, you need a load. That's why you got 5v. The laser diode will take whatever voltage it needs to work so you don't need to worry about it.
Second, this driver needs at least 6v to work, I recommend you use 5 or 6 AAs or AAAs to run this, the driver won't work for long when running it with just 4 1.5v batteries.
Third, your 5mW LD lased at 3mA simply because it's not that powerful so a small amount of power should be enough to power it up.
Fourth, if you're going to buy a 20x DVD burner to extract the diode you're going to need a 3 ohm resistor instead of a 5 ohm (2 10 ohm resistors in your case) because this diode is much more powerful and to get a lot out of it you're going to need to run it at 420mA. (this is considered the sweet spot)

And fifth, look at Gazoo's canned response for making calculations with this driver:

The LM317 is no mystery and very easy to work with. The following calculations always apply since it uses 1.25 volts for its reference voltage, and ohmís laws don't lie.

To calculate the resistor needed for a given current, take 1.25 and divide it by the current. So say you want to drive a SenKat diode with 250mA. 1.25 divided by .250 = a 5 ohm resistor.

Another way you could do this is to take 1.25 and divide it by the resistance. 1.25 divided by 5 = .250.

Next you will want to calculate the wattage of the resister needed. We know 1/2 watt resistors are common for use with the regulator. But to figure it out, simply take the 1.25 and multiply it times the current. 1.25 times .250 =.3125 watts.

The rule of thumb for the voltage going into the regulator is it should be 3 volts more than the voltage going to the diode. A SenKat diode running at 250ma's will have about 3 volts across it. Therefore a minimum if 6 volts is needed.
I recommend 6 NIMH batteries or 2 RCR123's for use with Daedal's driver.

This is why you need at least 8 volts to run the blu-ray. You will find when you have it hooked up, the voltage across it will be appx. 5 volts. But since it will only draw ~38mA, you can run it with a 9 volt battery.

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Old 04-15-2008, 11:00 PM #3
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Default Re: homemade driver questions

I think I will just put it on a 9 volt then. I wish they would have had a 6 x AA case but they only had an 8x one I figure with D's I have quite some time before they dropped below 6 volts total but I'll probably just use a 9 volt anyway. I think I have a stripped pop on cap thingy for one somewhere around here.

But I gotta ask, are you sure it's 420 ma? That seems crazy high. If I read it right, the 200mw diodes on mfgcn are supposed to operate at 115ma. And I figured the DVD one should be lower because it's not built to be on constantly instead of pulsing super fast.

btw I never really got that 1.25V thing. And that's probably because I actually have no idea what the voltage regulator does lol. I know how the ones in car alternators work and you have to set those and they only output at one voltage and they close and open the circuit super fast to lower the voltage to keep it as close to the target voltage as possible. I take it that's not what this one does? Well anyway, why would it matter that that's the reference voltage if that's not the voltage that's going in or coming out? For instance, why would I multiply 1.25V by the current to determine the recommended wattage rating for the resistor(s) when you said under load the circuit is 5 volts and the current is for example 420ma. Wouldn't that be 2.1 watts instead of 0.525? Anyway, if it is in fact 0.525 watts I should probably double check...if you wire two half watt resisters in parallel, they each take half the current and 0.525 wouldn't burn them both out, right? Btw I'm probably going to end up using sequential pots and set one permanently at 3 ohms cuz I couldn't find any resistors under 10 ohms and 4 in parallel won't quite fit, plus that'd look silly lol.
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Old 04-15-2008, 11:10 PM #4
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Default Re: homemade driver questions

You can't use a 9v battery because it's mAh rating is too low to drive a red diode. That's only for blurays since they don't need a lot of current.
And yes it's 420mA, a long open can diode being run at that current should put out around 250mW using a normal acrylic lens. (this current setting is only for the 18x or 20x long open can diodes) This is what they look like:



The LM317 always keeps a reference voltage of 1.25v between the Vout and Adj legs. When a LD starts to get warm it tends to draw more power, but the LM317 won't allow that since the 1.25v will start to go up and the LM317 will lower the output voltage until it's back down to 1.25v.
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Old 04-15-2008, 11:20 PM #5
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Default Re: homemade driver questions

ohhhh I get it. That's a smart way to regulate voltage lol. I dunno how to tell the style of a diode by looking at it but I'll post a pic once my DVD burner comes and I get the diode out of it. I think I do know what you mean by acrylic lense ones though cuz I'm really sure I've seen those. Btw don't all AAA. AA, C, D, and 9v batteries max out at 500 milliamps? (you meant ma not mah, right?) I know that'd be cutting it close with 420 going to the LD but wouldn't that do it?
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Old 04-15-2008, 11:25 PM #6
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Default Re: homemade driver questions

Well, it's regulating the current by regulating the voltage. (kind off hard to explain) ;D
I did mean mAh, an average 9v battery is around 150mAh, so it can deliver 150mA for one hour. Go ahead and calculate how much it would last when drawing 420mA. :P
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Old 04-15-2008, 11:54 PM #7
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Default Re: homemade driver questions

I didn't think that could possibly be right cuz alkaline AAA batteries are 900 to 1,155mah each! *And don't 9 volts technically have 6 alkaline AAAA battery cells in them connected with welded tabs? *And those cells are 625 mah each for a total of 3750 mah. *Though that info was from Wikipedia so anyone could have just made that up and their actual 9V page differs from the AAAA page in that they say alkaline 9V are 565 mah total. *Nickel Cadmium ones are 120mah but aren't all consumer brand ones alkaline?

Btw D are 12,000 mah each and I'm using 4, soon to be 5 :P I mean geeze, car batteries are only 100,000 mah! I can power that laser forever lol. *I actually just got a 225 cold cranking amp riding mower battery that's who knows how many mah but that's 12V and I don't wanna use another resistor so oh well lol. *Plus I'm using that to test all the car amps and subs I got for crazy cheap at an auction hehehe
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Old 04-16-2008, 12:55 AM #8
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Default Re: homemade driver questions

Quote:
Originally Posted by desolator144
I didn't think that could possibly be right cuz alkaline AAA batteries are 900 to 1,155mah each! And don't 9 volts technically have 6 alkaline AAAA battery cells in them connected with welded tabs? And those cells are 625 mah each for a total of 3750 mah. Though that info was from Wikipedia so anyone could have just made that up and their actual 9V page differs from the AAAA page in that they say alkaline 9V are 565 mah total. Nickel Cadmium ones are 120mah but aren't all consumer brand ones alkaline?

Btw D are 12,000 mah each and I'm using 4, soon to be 5 :P I mean geeze, car batteries are only 100,000 mah! I can power that laser forever lol. I actually just got a 225 cold cranking amp riding mower battery that's who knows how many mah but that's 12V and I don't wanna use another resistor so oh well lol. Plus I'm using that to test all the car amps and subs I got for crazy cheap at an auction hehehe
no all 9v batts have AAAA batts only energizer's do. Most 9v have little stacked cells inside
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