Red DIY DVD laser burner.

Dark_Horse · Jan 21, 2008

Thanks Gazoo,
This makes sense, it needs to have the supply power run through the DMM to measure the current draw.
I know this is not really related to the DMM/mamp reading, but I am guessing, if I were to add some resistors for limiting current, this resistor/s would be hooked up the same way, (in a series to the LD +or- side)?
Thanks,
Dark Horse

Gazoo · Jan 22, 2008

I am not familiar with that driver, but from what I understand yes the resistor goes in series, and it can go on either the + or - side.

adgmeijin · Jan 22, 2008

Hi kenom i have some test on my dvd LD driver using daedal 's LD driver i add another 10 ohm resistor on it and according to my DMM it is 3.9 ohms and i use 4.5 volts and LED for the test, DMM says that the output voltage is 2.3v and 3.5v on open circuit test, the max current to it is 210ma, the the 100 ohm trimpot was near to touch the lead before it comes to 0 ohm resistance, is it correct or can you give me an advice with this ? im using LG DVD 18x burner. im first timer to build DVD laser burner, I hope you appreciate what im asking for, thanks.

Dark_Horse · Jan 24, 2008

So I have been playing with my new Dorcy Jr, it work great, but... I am running right off of the Dorcy circuit, I would like to add some resistance to limit the current.
I have read about the resistor combos, but I would like to use a pot. I know this has been asked several times before, and was always shot down because of size, but I can easily fit the 100ohm pot that came in the kit from StoneTech, (Senkat). Electrically speaking, is there any problems with using this 100ohm pot to limit the current to 200-250ma on the "Dorcy-circuit"?
Dark Horse

Gazoo · Jan 24, 2008

The pot as I recall is rated for 1/2 watt. Assuming 3 volts at 250ma's. which should be about right for the SenKat diode, you would need a 3/4 watt pot. Use ohms law and take volts times amps and you will get .75 watts.

http://www.the12volt.com/ohm/ohmslaw.asp

You can still try it, and even if the pot shorts out or causes an open circuit your laser diode will be ok. But it probably won't as long as you keep your duty cycles reasonable.

Dark_Horse · Jan 24, 2008

Excellent info Gazoo, learn more everyday. I think I will research the wattage rating on Senkat's pot first, and give it a try, I will let you know.
Dark Horse

adgmeijin · Jan 24, 2008

hey gazoo im trying to use 4 pcs LR44 to make 6 volts to my DVD laser, i test it using LED first and according to my DMM the output across LED was reading 2.6-2.9v @ maximum of 230 mA, do you think that is good for the LD? please clear me up , thanks.

Gazoo · Jan 25, 2008

adgmeijin said:
hey gazoo im trying to use 4 pcs LR44 to make 6 volts to my DVD laser, i test it using LED first and according to my DMM the output across LED was reading 2.6-2.9v @ maximum of 230 mA, do you think that is good for the LD? please clear me up , thanks.

LR44's will sag quickly and might run your laser for a few minutes. You are better off using a pair of RC2's. The minimum voltage needed to run Daedal's driver is 6 volts. When the voltage drops to less than 5.8 volts or so, the regulator will start to drop out. You can tell by measuring the voltage between the output and adjust of the regulator...it should be 1.25 volts. I know I told you this before, but the very best solution is 6 nimh batteries or 2 RCR123's.

danq · Jan 25, 2008

Gazoo said:
The pot as I recall is rated for 1/2 watt. Assuming 3 volts at 250ma's. which should be about right for the SenKat diode, you would need a 3/4 watt pot. Use ohms law and take volts times amps and you will get .75 watts.

I'm not clear exactly what the "Dorcy circuit" is, but just to clarify the theory a bit, the power that the pot must dissipate is dependent on the voltage across the pot, not the whole circuit... if there's anything (like another resistor or a LD) in series with the pot, it won't get the whole voltage of the circuit.

For example if the driver is "Daedal's" LM317, the resistor leg will always be 1.25 Volts (because that's what's regulated). So in that case a 10 ohm resistance would draw .125 Amps; the resistor would thus have to handle .125 Amps X 1.25 Volts = .15625 Watts or just over 1/8 Watt. In the case of an LM317 circuit you'd need to run at 400mA (using about 3 ohms) to get up to 1/2 Watt.

DanQ

Gazoo · Jan 25, 2008

Edited...Never mind...I understand what you are saying. So how would we calculate the resistor needed if putting it in series with the diode?

danq · Jan 25, 2008

well now... that depends - which is why we use regulator circuits

you can take a rough guess based on the specified forward voltage of the diode - but that varies with operating temp, etc.... as does the battery voltage.

So if you start with a 6V battery, with a 3Vf diode, then a simple series R will have 3V - except for if anything changes, which they will... which is why we bother with regulators, especially when dealing with non-hardy LD's like the Blu-ray.

You can get away with just a resistor and a battery and a LD, as long as the R is set to give the max tolerated current given the maximum voltage of the battery and the minimum voltage of the LD. That way the current has no place to go but down so it won't run away.

DanQ

Gazoo · Jan 25, 2008

Those are all very good reasons to use a regulator

Thanks for the response, I do understand your explanation.

Dark_Horse · Jan 25, 2008

I'm not clear exactly what the "Dorcy circuit" is, but just to clarify the theory a bit, the power that the pot must dissipate is dependent on the voltage across the pot, not the whole circuit... if there's anything (like another resistor or a LD) in series with the pot, it won't get the whole voltage of the circuit.

I was unclear, I am trying to limit the current to my GB LD in a Dorcy Jr, I was looking for an alternative to a resitor combination for limiting the ma to the existing "regulated" circuit from the flashlight.
Thanks,
Dark Horse

Kenom · Jan 25, 2008

ya know I don't see a problem with the potentiometer in yours. I use 1/4 watt resistors in my lasers and havn't had a problem 1. I will include a picture of the driver not that that's necessarily going to tell us what it is. the one problem I've seen in using the potentiometer from SenKat's driver package is it's pretty high resistance. usually i'm only using 3ohms, 5 ohms or 6.something ohms. soo real fine tuning on a larger pot.

Dark_Horse · Jan 25, 2008

Sounds like the pot would be too sensitive, maybe I will just go with the resistors, but I may try the pot in the next Dorcy, (I just sent Senkat a big order, (big for me).
Like Kenom, I am trying to find an ideal, off the self solution, that will provide a simple mod to an existing host, I have fallen in love with the Dorcy, but stock it is too much current for the GB LD.
Gazoo, If I used an open-can LD, like from the DVR115, in place of the GB LD, would I be OK with the 350ma that my Dorcy is putting out without resistors, then I would just need to add a capicitor to the LD, and I should have a reliable-long-lived that can burn like the GB LD, maybe a little better?
BTW, Where do I buy the Merideth module, I would like a little better optics?
Thank you all,
Dark Horse

Dark_Horse · Jan 25, 2008

Kenom,
Where did you find the Laser warning stickers for your Dorcy Jr?
Also, do you know the Thread specs for the lense assy in the Axixis modual, I need to buy a tap so I can make my own heatsink/LD module, and thread the lense directly into the heat-sink, eliminating the axixis mod all together, like on the custom barrels. It is almost certainly metric.
Thanks
Dark Horse

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