DIY Homemade laser diode driver

Chris. said:

To minimise the current initially, should the potentiometer be at its minimum or maximum value?

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Maximum value - most resistance, least current.


Test it on some LEDs first.. And then discharge the capacitor.

To test it to a higher current you would need more LEDs in parallel. With five you could test it up to 100mA, maybe 150mA before they would start dieing..

But you can just as well test it on one only, and slowly adjust the current up to 20, maybe 30mA (if you don't care about the LED.. It wouldn't die tho at 30mA). Even this would show you, if the circuit is working - if you put everything together right, it should be.

Guys.... IT WORKS!!!
Omg ;D ;D ;D
Totally worth it. Now just to fit the little thing into the Aixiz casing... I REALLY hope I dont crush it

I'll take some pictures tomorrow, my circuit is pretty small

Chris. said:

Guys.... IT WORKS!!!
Omg  ;D ;D ;D
Totally worth it. Now just to fit the little thing into the Aixiz casing... I REALLY hope I dont crush it  

I'll take some pictures tomorrow, my circuit is pretty small  

Click to expand...

Good to hear. I know how you feel..

But make a new thread for pictures and other stuff about your laser.. This should be for LM317 driver discussion only..


EDIT: Although a picture of the driver circuit itself might not hurt..

Ha! LEDs
I always just short it out with my multimeter to make sure the current is low
<50mA isn't going to kill anything

Well I used:
50 ohm potentiometer
16v33uf cap
8x DVD rw diode
The pot is at about 40 ohms at the minute, I've so far been unsuccessful in checking the current as my multimeter has the habbit of shorting out the diode and taking no readings..
(Yes inserted properly e.g. in series)
Just ordered a laser check to test the output.
As a rough guide, It just burnt cleanly through a bin-liner and lit a match(safety) with no lens at short range. What mW output might this be in the range of?

woop said:

Ha! LEDs
I always just short it out with my multimeter to make sure the current is low
<50mA isn't going to kill anything

Click to expand...

That is also an option, and you could test it up to the full current this way. The voltages would be very small tho, but this doesn't matter, as it would still show if it works.

Good idea.. Thanks.

Chris. said:

Just ordered a laser check to test the output.

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I think the LMP-1 is a much better meter and there is a group buy for them. So you might want to look into it and cancel your order for the lasercheck...but of course it is up to you.

Chris. said:

The pot is at about 40 ohms at the minute, I've so far been unsuccessful in checking the current as my multimeter has the habbit of shorting out the diode and taking no readings..
(Yes inserted properly e.g. in series)

Click to expand...

On some meters you have to switch the socket for the red probe, depending on the current you measure..

For example, if i measure up to 200mA i use the same socket as for voltage measurement.. For higher currents i have to use the other socket, above this one.

In series it is impossible to short anything.. The multimeter itself has to pretend it is a short, when measuring the current. If it is set wrong tho, for voltage measuring, it will pretend it has unlimited resistance and prevent the current from flowing. The same could happen if you use the wrong socket on the meter.


BTW: On a 8x DVD LD you should be carefull about too much current and heat.

Yeah, I have one socket for <200mA and one for <10A
I'm convinced its providing (theoretically) infinite resistance as if it were in volt meter mode..

Chris. said:

Yeah, I have one socket for <200mA and one for <10A
I'm convinced its providing (theoretically) infinite resistance as if it were in volt meter mode..

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Oh! I know what this is... It's the fuse!

Mine was also dead when i got it, so i shorted it and later got a new one..


Short the fuse inside the multimeter and you will be able to measure the current. Later buy a new fuse..

BTW: There is also a better and more exact way of measuring current here..

You can put a 1/2W, 1 Ohm resistor in series with the LD.. Then you measure the voltage drop (in millivolts) across it, and the voltage drop in mV is equal to the current in mA.

It will not affect the behaviour of the circuit in a bad way. It will have to put out slightly more voltage, but not much.

This is also safer than putting the multimeter in series, since you don't have to disconnect the LD, or anything else..


It can also be done with a different value resistor, but you would have to calculate the current (I = U / R) and the voltage drop would be higher..

You will want to use at least a 1 watt resistor.

Gazoo said:

You will want to use at least a 1 watt resistor.

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That is true, my bad...


Thanks Gazoo!

Thanks for all the help; You were right about the fuse IgorT.. I must have blown it when I was building my coilgun. A peice of mechano soon sorted that out though.

IgorT said:

[quote author=Gazoo link=1185701612/510#523 date=1194819557]You will want to use at least a 1 watt resistor.

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That is true, my bad...


Thanks Gazoo![/quote]

I say at least because it depends on which diode you are driving and so on. But lets use the GB diode for example. The voltage across the diode will be ~2.85 volts with 250ma's of current. 2.85 X .250 = .7125 watts. Therefore for higher currents I would use a 2 watt resistor.. Since we are building the circuit we might as well use a 2 watt for future diodes and what not. Really this is only necessary for experimentation like for a lab laser since it is easy to calculate the resistor needed if using the LM317 as a current regulator. For the open can diode.... I have run 600ma's into it and my resistors get hot. I need to see what the voltage is on the diode with that current..

Added..I checked the voltage across my open can diode running with 600ma's and it is 3.47 volts. Fortunately I am using 3 watt resistors and a 3 watt rheostat. I have two 1 ohm resistors connected in series with the rheostat so current is limited to ~600ma's when the rheostat is set to no resistance. I did this to prevent accidentally blowing the diode..

I just finished mine.
it workes nice. ;D
Time to put the LD into the AiziZ housing.
Soooo close!!