LASER (from cannibal-ized barcode scanner)

Discussion in 'General Electronics Chat' started by Metalfan1185, Oct 31, 2008.

  1. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
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    ok, laser element that has 3 leads, i dont know too much more.

    Legs:

    1 2 3

    Voltage from 1 to 2 while off :
    5V

    Voltage from 1 to 3 while off:
    2.8V

    Voltage 1 to 3 while switch is pressed (scan)
    4.4V (i would image drop from load)

    Voltage from 1 to 3 while on:
    1.6V


    All voltages approx.


    My question is how can i drive this thing? you know? like how can i get a battery on it and use it like similar to a pointer, or use a switch to power it on? any ideas?
     
  2. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    nothin, huh?
     
  3. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    Honestly, I don't know what driver circuit exists and if it is a part of a large PCB.

    Laser diodes include the actual laser element, which is treated like an LED from a circuit design point of view and a photodiode for feedback. The photodiode takes a measurement of the emission (facing opposite to the normal emission direction) in order to close a feedback loop. The actual laser diode is very temperature sensitive and ages, so it is necessary to have the photodiode monitor the actual light produced.

    The drive circuit uses this feedback to control current through the laser. Designing these circuits requires some specifications, which I am assuming you do not have.

    Steve
     
  4. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469

    Steve is correct.

    Also, it would be risky for anyone to guess the pinout of your laser based on your measurements. The lasers that I've seen have the anode of the laser and the cathode of the photodiode tied together. This leaves the cathode of the laser and the anode of the photodiode free. Hence, this is why you have three leads. Usually the common lead would be connected to the positve supply rail. But, these are just guesses, based on the most common laser packages and drive circuits.

    Some words of caution. Both the laser and the photodiode are static sensitive so be careful handling, or they will be damaged permanently. Also, you have not said anything about the laser output power or wavelength, and your laser class may be dangerous. Lasers can damage the eyes permanently. I've noticed many people are very casual about laser pointers. Those can be dangerous, but if you pull a laser out of a piece of equipment, you may have an even more dangerous laser on your hands.
     
  5. Metalfan1185

    Thread Starter Active Member

    Sep 12, 2008
    146
    0
    Thank you for the responses, i figured it was a little complicated. I just pulled this thing out of the trash and i really dont care if i burn it out or whatever, but i never really tried to play with stuff like that. So, in a sense of risk, there really isnt any. I also know about the dangers of a laser.

    I understand that the photodiode is used to monitor the output of the laser, like steve said. but im thinking that just for the hell of it, i may just try to wire up just the diode.

    if i mess it up, then it goes back in the trash where i found it lol

    any ideas for a series resistance? maybe i should hook up a 1k in series with a battery and use a variable resistor a for an adjustment.
     
  6. steveb

    Senior Member

    Jul 3, 2008
    2,433
    469
    Yes, you can hook it up just like a diode, but the main problem is that you don't know the rated current and voltage of the laser.

    You can work slowly to figure this out though. I would recommend a larger supply voltage like 12VDC rather than 5VDC initially. Then perform various tests. Start with a 10K ohm series resistor which will produce an approximate current around 1 mA. You can then measure the exact laser voltage and current. Now the question will be, "Is the laser lasing. That is, does the laser produce a nice powerful beam. I would expect that at 1 mA you will not have a good powerful beam yet. Keep decreasing the resistor gradually (that is, 9k, 8k ... 1k, 900, 800 ... 500 using standard value of course, and no smaller than 470 ohms) until you see the laser light suddenly start to get very bright. Now you are near the threshold current of the laser. Record the voltage and current up to the threshold current and then report back the data to us. The difficult question is going to be just how much current you can run at without damaging the laser, either due to heating or overdriving the current. Once we see the data, we may be able to match it up with existing lasers and estimate the usable drive current.

    Oh, and the color is helpful. Is it red?
     
    Last edited: Oct 31, 2008
  7. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
    1
    I took apart a similar machine before and found similar laser modules. They were attached to their own drive circuit, so I just had to apply the 5V. The good part of the find wasn't the diode, rather high quality collimation optics.

    Steve
     
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