DIY Homemade laser diode driver

do i nedd to use the exact parts listed???
i have a diode that is 1N4148, not 1N4001. i have a capacitor thats similar to the one in the schematics.

can i use 3 Volts, not 6 volts. if so, do i need to modify it?

hmmm.

do i nedd to use the exact parts listed???

i have a diode that is 1N4148, not 1N4001
It looks OK on the data sheet http://www.nxp.com/acrobat_download/datasheets/1N4148_1N4448_5.pdf
. i have a capacitor thats similar to the one in the schematics.
Similar colour? similar shape? ....more info needed

can i use 3 Volts, not 6 volts. if so, do i need to modify it?
If you read the first few pages of this thread you will find where it is explained why you cannot use 3 volts, 6v min for red 7.2v better

Regards rog8811

Alright, I am having a bit of trouble with my driver and test load.
Probably just my lack of understanding but here goes.

I was powering my circuit with 4 AA alkaline batteries which I discovered
is a bad idea by reading this thread. That being the case I am now using
6 1.2V NiMH AAs. Problem is they are puting out 1.4V not 1.2 so I am getting
about 8V from my battery pack. The LM317T is getting warm while I am testing
with my dummy load. On my dummy load I am getting 3.3 to 3.4 volts at 200mA.
is this normal for the test load circuit. I tried reducing my input by only using 5
batteries at 6.67V but the reading on my test load stayed the same 3.4V.
I am concerned that is too high for my LD but I don't know if the test load actually
draws the same amount of power that my LD does. Is it safe to connect my Laser
to the driver with the test load showing 3.4V? Please help!

testing the current.
i know you say LED's, but how many and what specs, if you dont know the specs of the led wont it be very unreliable.

is there a way using a multimeter to get the exact current.
Can someone please post a procedure in testing the current for this driver board.

thanks dudes....

Galdor - If you change the voltage by adding/ removing a battery and the voltage stays the same, this means that your driver is indeed regulating

Don't worry about the voltage. As long as the current is regulated (as it seems to be in your case) then voltage should not be a problem and you should be able to hook it up to your LD.

Short the cap first!

Thanks pocketfluff. I ended up using an 8x LD I burned out as a test load and it worked
much better than the four 1N4001 diodes. Gave me a much better idea of what my operating
voltage would be with the working LD connected. My laser is complete now and working great. It
is an 18x open-can and I am running it at 220mA. Now I am thinking about getting a glass lens. ;D

wheres the FAQ

nvm i answered my own ?

I am new to the hobby of laser construction but i am finding te whole thing fun. I went out to radio shack and bought my parts so i could construct my driver while my diodes are on order. I followed daedal's instructions with the exception of using a 25 ohm pot which i am going to replace with the 1k pot i am getting in the morning from radio shack and 4 AA batteries putting out 6.1 volts.

My problem is my readings don't match what i was expecting. I am getting the correct 5 ohms from the resistors, and a range from full resistance of 42 mA to little resistance of 250mA, which all looks fine but then i look at my voltage and i am getting 4.8 volts at the laser diode hookup point. I discharged the capacitorbetween readings both before and after thinking the voltage was that but it appears my circuit is actually at that voltage. I checked all my solder points and where everything is connected and can't find the problem. If i have this right the LM317 should take 3 volts off the top and the IN4001 should take another .7 leaving me at 2.4 or somewhere close, have any ideas?

i would really apreciate any input someone might have

I am new to lasers like you but I suppose you're measuring the volts without a load, i.e. with the DMM connected where the LD should go. If you search this thread you should find plenty of information on how to create a load to test the real output of your driver.

Please "experienced users" correct me if I'm wrong .
Have fun ^_^

So, I have a sincere question. Maybe I'll sound like a n00b, but logically this makes little/no sense to me (But maybe that's just me). What is the point of the capacitor, when there's a completed circuit as a result of the 1N4001? How does the capacitor help? I honestly don't understand it. I know that a capacitor is supposed to absorb electricity, and when it's full it acts as an open circuit, but if there's a diode (1N4001) that completes the circuit, how does the capacitor help?

How does the capacitor help?

Click to expand...

It will help protect your LD from overvolt spikes on switch on/off. The diode protects against accidental reverse voltage connection.

Have you measured the reference voltage? it should stay at a constant 1.25v throughout the range of the pot, if it does that it is working OK.

See first few posts on this thread.....
http://www.laserpointerforums.com/forums/YaBB.pl?num=1197651171

Regards rog8811

thanks for your help... now i know exactly how to test my current...

ok so i went to radio shack and got all the stuff i needed. The only thing they didn't have was a 100 ohm pot. They guy said i could use the closest thing they had. Which is a micro 1k ohm pot. He said i will just have to make sure and check it with a multimeter before i connect the diode to make sure im not going to blow it. Does this sound right?

Now im wondering if i am going to be able to get 420ma with this setup.

1k Ohm Pot
10 Ohm resistors
10MF 16v Tantalum Capacitor
lm317T Adjustable Voltage Regulator
IN4001 Silicon Diode load

Should i be able to set a 420ma current with this setup ?

EDIT: Am i suppose to be using a 3 ohm resistor for this application?

Yes, you are supposed to use a 3-ohm resistor for a maximum of 420mA.