DIY Homemade laser diode driver

You don't seem to have the diodes listed in your cart so you will need to add them. Also not sure why you need the 100k trimmer or the 10k resistors. They have far too high a resistance to be of use.

Cheers

XG

You have got 2 capacitors there you will only need the radial-lead cap [highlight]item number: 2102512[/highlight]

Thanks guys, I have updated it, Hopefully its correct now :-[

Okay that's better.

Now the 1000 ohm 15 turn pot is a bit high. As you have the 25 ohm rheostat I would ditch the 15 turn pot.

If the pot is linear that works out at 66.66 ohms per turn. Anything over 15 ohms (a qtr turn of a 15 turn pot) between the adj and vout pins on the LM317 will not have enough current to drive the LD.

xgeek said:

Okay that's better.

Now the 1000 ohm 15 turn pot is a bit high. As you have the 25 ohm rheostat I would ditch the 15 turn pot.

If the pot is linear that works out at 66.66 ohms per turn. Anything over 15 ohms (a qtr turn of a 15 turn pot) between the adj and vout pins on the LM317 will not have enough current to drive the LD.

Click to expand...

OK thank you, the 1000 ohm 15 turn pot is the lowest resistance RatShack has, guess I'll have to purchase the pot from elsewhere.

But why the need for the extra pot when you have the 25 ohm rheostat :-?

xgeek said:

But why the need for the extra pot when you have the 25 ohm rheostat :-?

Click to expand...

Uhhh... cuz i'm a tard before my coffee kicks in. :

Thanks for the guidance , Now to purchase them.

I appear to be blind (no worries, don't have my lasers yet), but I just can't find the layout for the driver you can buy from senkat.
Is the circuit layout only available if I buy it from him, or is it just hidden somewhere (or am I just únable to look properly)?

philguy said:

I appear to be blind (no worries, don't have my lasers yet), but I just can't find the layout for the driver you can buy from senkat.
Is the circuit layout only available if I buy it from him, or is it just hidden somewhere (or am I just únable to look properly)?

Click to expand...

Heres one, I not sure who's anymore.

I've used that exact 1K pot in my driver and it works okay. It's just a waste of about 14 turns which makes fine adjustments a little difficult, but it's not bad for the size. It'll do the job as any other pot would.

Thanks, I'll keep that in mind while I build my first 3, I'm sure I'll need and want to make a few changes.

If you think about it, though, the 15 turn 1K ohm pot would be more precise to adjust than the 1 turn 100 ohm pot: 1000/15=66.7 ohms/turn as opposed to 100 ohms/turn with the other. You just turn it to within 1 turn of 0 ohms then adjust it from there. The only difference would be that if there's, say, a 5% accuracy tolerence, the 100 ohm pot could only be off by 5 ohms where the 1000 ohm pot could be off by 50. So both types have their pros and cons - it may or may not be worth it to special order the 100 ohm pot if you can't get it from Radio Shack.

The resistance of the pot might be linear, but the amount of current going to the diode will not be linear. In other words, when you start to get in the area of the least resistance, the current begins to jump up...I hope that makes sense..

I have an assortment of pots, from large to small, I just have to check to see what the resistance of each one is.

Hey ive just got a few quick questions

1) Im a little confused at where to place the DMM in the circuit to measure voltage and current. Can we just attach the terminals of the DMM to the wires that would be going to the laser diode to measure the voltage going to the diode before we attach it? and where would you place it to measure the current?

2) I was wondering... we are aiming to get 2.5-3 V to the LD and 250 mA. but if you plug that into P = VI you would get about 750 mW? isnt that a bit much, or am i calculating wrong?

3) I think my circuit is not correctly wired (or im not measuring at the right spots) - when i measure the voltage, it starts at about 2.5 and keeps going down and down and down (even if i unplug and reconnect the terminals of the DMM). but if i measure it again a few minutes later, it goes back to about 2.5 v and keeps going down and down.. if thats just a crazy result, dont worry about it, im going to make another circuit and test it out - any answers to the above two questions would be enough

thanks a lot for your help guys

dil

If I put the capacitor in parallel with the battery before it goes into the lm317 would that still be effective and do an ok job of filtering any spikes?