Why does my driver not work?

[jawsykilla]

Hi, I am a noob when it comes to laser circuits although in my time I have modded console circuits and stuff. I got the urge to make a laser, so i acquired a range of laser diodes from dvd players and dvd rewriters. Now I'm under the assumption that the ones from dvd players are no good because they work on an infra-red wavelength of the EM spectrum? Even if that is true I do have in my understanding a red laser diode that should work. So I built a driver circuit as shown in the picture below which I found the diagram for floating around somewhere. I connected a 9.6v battery and nothing. Also I'm not sure if the pot is nackered but twisting the screw thing does nothing. I have measured the pd across the battery and it gives me 22v and I can get a pd all the way to the diode but if I measure the pd across the laser diode pins I get 0. Also i would like to clarify, which pins do i actually need to connect +ve and -ve to on the laser diode?

You can see my circuit Here

 

[KiLLrB]

You asked which leads to connect to the diode but it appears that youve already connected it. If you hooked it up backwards you likely fried it. Also if you apply volage to the cap and didnt drain it before you hooked up the laser diode you will likely pop it. Check the 1Nxxxx diode to make sure it is in the circuit the right way and double check the LM317 connections (make sure you have out, adj and in located correctly)

 

[jawsykilla]

Hi, yeah i have connected it using the diagram I found on this forum. Which I presume is correct, I just wanted to make sure so I don't think i soldered the connections on wrong to the laser diode. As for the capacitor I did short it before connecting the laser diode. The 1N4001 and LM317t connections are also the right way round. So i'm not sure what is going off. I just connected a different laser diode and i'm now getting a pd across the laser diode but once again no laser is appearing. What is adjusting the LM317 supposed to do because it seems to do nothing.
Cheers,
Jordan

 

[KiLLrB]

Hi, yeah i have connected it using the diagram I found on this forum. Which I presume is correct, I just wanted to make sure so I don't think i soldered the connections on wrong to the laser diode. As for the capacitor I did short it before connecting the laser diode. The 1N4001 and LM317t connections are also the right way round. So i'm not sure what is going off. I just connected a different laser diode and i'm now getting a pd across the laser diode but once again no laser is appearing. What is adjusting the LM317 supposed to do because it seems to do nothing.
Cheers,
Jordan

Are they IR diodes? Take a cheap camera or a nightshot capable camcorder and see if you see any IR.

 

[Morgan]

Hi jawsykilla and welcome to Laserpointerforums,

In your first post it says you get a pd of 22V?! Do you mean 2.2V? That does sound about right for a red or IR diode but we can't be certain where you are testing. The circuit, 'looks', right. Cap is the right way round, reverse protection diode looks to be right, etc. (bit difficult to see on such a huge pic but...). You've shorted two of the legs of the pot, right? Can you measure the resistance of the pot and see if it is serviceable?

Adjusting the LM317T via the pot changes the rsistance to allow it to give a constant current. It is actually a voltage regulator but in this setup it regulates the voltage to whatever the LD needs and due to Ohms law provides a higher or lower current to maintain that voltage. (The, 'ins', and, 'outs', of this process are best left to others to explain in detail).

KiLLrB is absolutely correct to use a cheap digital camera. Your mobile phone will probably give you good results too. The CCD sensors are sensitive to IR wavelengths so will pick up the IR. If you're not sure your camera is sensitive, try pointing your TV remote at the camera and observing the IR LED. If you see a blueish flashing doing this then you are, 'seeing', the IR. Don't be tempted to look directly at the diode as, 1. You don't know if they are IR and, 2. You don't know what power they are. (googles will soon be top of your shopping list!)

As to pinouts of the diodes... That's a tough one as we don't know from which drive they're harvested, (knowing this is unlikely to help either, unfortunately), and the pinouts vary. To check your driver is actually functioning to start with you could try an LED. You may be overdriving it but they are cheap and at least you'll confirm the driver is working or not.

Good luck and keep us posted...

M

 

[jawsykilla]

Hey Morgan! I already did the camera test for IR yesterday and nothing is coming out of the diodes what so ever. As for the 22v PD I meant to type 10.1v but for some reason I didn't. Yeah I connected the two legs on the pot because that's what the diagram illustrated, it seamed a bit funny though when I did this. I just measure the resistance across the pot and I'm getting 107ohm from pin near lm317 to furthest pin and from near lm317 to middle pin of 73 ohms. I took these measurements after separating the 2 shorted pins. When these 2 pins are shorted i get 68 ohms. I just hooked up a bulb to the circuit in replace of the laser diode and i get nothing. Do I need to try with an LED?
Cheers,
Jordan

 

[jawsykilla]

Anyone?