Laser driver with feedback

[Zarniwoop]

Uh, that's 400ma in, not 400mW out.
On Hemlock Mike's power curve for the open-can LDs that's about 225mW.
Still not too shabby.

 

[Greyfox]

Second confirmation that many DVD drives don't use the PD sense. Here's an idea of why:
Different discs perform differently for burning. Even discs of the same model and batch will react differently, especially when you throw in the variable of speed above everything else. By the standard for burning DVDs, they have developed a way to solve this.
For adjustable high-speed drives, they run burn tests in a designated spot on each disc at different power levels to determine what works best. This makes the feedback design almost pointless for them.

 

[Gazoo]

yea gazoo those are very low powered tecs, i think you could have some fun with a larger one that could keep the diode at a lower temperature even when running at 600ma

i would really like to buy some as i only have the high powered kind and can't be run off of the psu inside my lab laser i made without the transformer overheating

I am sure if I had more cooling to the heatsink the peltier is mounted to it would help. I haven't been able to run the peltier to its full potential because my power supply isn't powerful enough to run both the LD and the peltier... I will do some more experimenting..I might get a 40mm fan and mount it to the heatsink. Anyway a 5 minute run would have been impossible without the TEC.

 

[woop]

"Behold, is this freaky or what ? I just hit the 400mW mark on the dot ! And it was going steady down to 391mW"
i think its mW! in the picture, he has the laser meter set up and its reading exactly 400mW. he is feeding the laser 700mA.

For adjustable high-speed drives, they run burn tests in a designated spot on each disc at different power levels to determine what works best. This makes the feedback design almost pointless for them.

thats not all that feedback is useful for though.
if you calculate the required current at the start of the write, when the laser is cold. as the laser heats up its power output will decrease. this is the whole idea of feedback, so you can set it to a power level, and it will always go to that level, no matter what the temp is or if the battery voltage is high or low (as long as its high enough to give the diode full voltage)

i am certain that dvd burners would need feedback of some sort, probably not in the actual diode though.

on that note, yeah i know feedback is not necessary for general lasering stuff, but i just thought it would be cool.

On Hemlock Mike's power curve for the open-can LDs that's about 225mW.

were those the GB power curves? the ones done by hand?
I am actually thinking of rigging up a power curve setup. I don't have a laser power meter, so it will just be using a solar cell or phototransistor and having relative results, unless anyone has any experience calibrating a laser meter with household objects? :-?
I will hook up the current, power and maybe temperature readings to the ADC input of a microcontroller and transmit readings by serial to my PC which will draw a graph in real time thinking this might be of some use!
anyone tried this before, or something similar?
I won't have any time to do it until next week, which is when i will be getting a 112D laser too

 

[Kenom]

that laser diode did NOT put out 400mw. in the reading he took there was no ND filter in place so the reading was innacurate. You can look at the picture and see it. I love how everyone thinks this diode is capable of so much and really isn't. above 200 yes 300 no 400 hell no!

 

[Zarniwoop]

woop - That graph has 2 curves - one is a GB i.e. 16x, and the other is an open-can type.
I agreee - I can't see one of these doing 400mW. 300 is at the edge.

As it happens I'm experimenting with making a power meter too.
Things to consider - the spectral response of a solar cell varies (fairly linearly) with the light wavelength. You've also got to reduce the light that hits the cell to the point that you don't saturate it with whatever you max mW will be. If you use a lens to spread the beam, it will refract different wavelengths to different degrees, and some lenses will absorb some wavelengths like UV. Then of course there's calibrating it.
I may never get anything useful out of this but it's a fun experiment.

 

[Gazoo]

that laser diode did NOT put out 400mw. in the reading he took there was no ND filter in place so the reading was innacurate. You can look at the picture and see it. I love how everyone thinks this diode is capable of so much and really isn't. above 200 yes 300 no 400 hell no!

Well 300mw's is possible with 600ma's as I did it last night. Of course I am not sure how long the diode will last, and I will be placing another order for a couple of 112D's just in case... ;D The beam is a sight to behold at that current level but is still not as bright as my X105.

My opinion is the open can is just as capable as the phaser diode and maybe even more so. However for a long lasting experience with the open can I would keep it at 400ma's which will still give an output power a little in excess of 200mw's. One thing for sure is the open can diode is capable of much more than any closed can diode I have used, but it does come at a price and there is no guarantee every harvest will be a success, although I have harvested two 112D's and one was successful.

You are right about the ND filter...and I too do not think 400mw's is possible from an open can.

 

[woop]

woop - That graph has 2 curves - one is a GB i.e. 16x, and the other is an open-can type.
I agreee - I can't see one of these doing 400mW. 300 is at the edge.

As it happens I'm experimenting with making a power meter too.
Things to consider - the spectral response of a solar cell varies (fairly linearly) with the light wavelength. You've also got to reduce the light that hits the cell to the point that you don't saturate it with whatever you max mW will be. If you use a lens to spread the beam, it will refract different wavelengths to different degrees, and some lenses will absorb some wavelengths like UV. Then of course there's calibrating it.
I may never get anything useful out of this but it's a fun experiment.

i was thinking about such things like saturation. i don't think the frequency response is going to matter that much, as i am only going to be using it with reds at the moment.
how are you going to capture the data?
what sort of sensor do commercial meters use? i am thinking of a phototransistor simply because it is easier to implement, i will need a voltage that varies with light intensity from 0-5V for the ADC to be most accurate, so to use a solar cell i will need an amplifier, and that adds another layer of non-linearity
unless i have some way to calibrate it i can pretty much forget about getting accurate mW readings, but i should still get an accurate curve, and the current measurements are easy enough to get accurate.
I could always compare my graph to someone else's and calibrate it that way, assuming a similar diode is being used and the temperatures are the same.

 

[Zarniwoop]

So as not to hijack this thread further, I'm starting a new one:
http://www.laserpointerforums.com/forums/YaBB.pl?num=1194745802/0
for the DIY power meter discussion.