Laser Pointer

[Dan East]

I bought a laser point in order to extract the laser emitter for a project. On disassembly I find that the laser emitter (is it a laser diode?) is a tiny circuit board sandwiched between two metal plates (one is copper looking, the other silver). There appears to be an IC epoxied onto the main circuit board, and it is connected to the laser emitter when a push button is pressed.

I have a few questions about this. Is the emitter a Laser Diode? Does it require some sort of driver, and if so, what does the driver do? Why does it require a lens if it is a laser?

It is looking like I will probably have to extract the entire circuit board and use it to power the laser, depending on what the driver (if there is one) does.

Thanks.

Dan East

 

[dknguyen]

I bought a laser point in order to extract the laser emitter for a project. On disassembly I find that the laser emitter (is it a laser diode?) is a tiny circuit board sandwiched between two metal plates (one is copper looking, the other silver). There appears to be an IC epoxied onto the main circuit board, and it is connected to the laser emitter when a push button is pressed.

I have a few questions about this. Is the emitter a Laser Diode? Does it require some sort of driver, and if so, what does the driver do? Why does it require a lens if it is a laser?

It is looking like I will probably have to extract the entire circuit board and use it to power the laser, depending on what the driver (if there is one) does.

Thanks.

Dan East

Yes it's a laser diode. It does require a driver I believe. It might be jsut be a custom voltage regulator or something. From the link below it looks like some drivers (and laser diodes) have/need temperature compensation. Eitherway, just take the entire assembly and use it. I wouldn't mess around with it, and don't remove the metal plates.

Lasers can still have lenses. They still do have a small spread angle and maybe the lens helps that. It could also just be for protection or whatever.


https://www.repairfaq.org/sam/laserdps.htm#dpsldd

Everything from beginning up to the "Integrated Circuits for Driving Laser Diodes" is for sure useful to you.

"Visible laser diodes generally have very precise drive requirements. Too little current and they don't lase; too much current and they quickly turn into poor imitations of LEDs or die entirely"

 

[Dan East]

Thanks. I'll just keep the assembly together. Very interesting information on that site you linked to.

Dan East

 

[things]

the lens is for colluminating the laser beam. whenthe light comes out of the diode, it spreads out very quickly, so the lens "focuses" it to a narrow beam

 

[Dan East]

So if it is an unfocused beam, then what is the difference between it and an LED? The intensity? The frequency of the light?

Dan East

 

[Dan East]

One other question. This will be for a break-beam type sensor. Instead of leaving the laser on continuously, I can poll it several times a second. The same PIC that reads the sensor can also control the laser. So my thought is to check the sensor (if high then there is too much ambient light), enable the laser, check the sensor, then disable the laser.

The question is timing. How fast will a typical laser pointer illuminate when power is applied? Is it as responsive as a typical LED? Will a laser pointer running at, say, .1% duty cycle (1 ms per second) pose a risk to eyesight? This thing will be right at eye-level for some children, so I might have to go with a IR LED and lense instead for safety.

Dan East

 

[dknguyen]

Technically an LED just emits photons while a laser diode has self-amplification going on. Probably doesn't answer your question, but yeah...

Maybe you should try making it lower than eye level for children. A neat blinking light is still a neat blinking light. An IR laser is certainly not better though since there is no reaction to turn away. All IR lasers (if I'm not mistaken) are rated class III or higher because of this.

Unless you mean regular IR and not an IR laser. CHeck out the IR rangefinders and proximity sensors from Sharp Optoelectronics.
https://www.sharpsma.com/Page.aspx/...b-a14f-92e2bd34f1c7/Distance_and_Air_Sensors/

 

[Dan East]

It would be an IR LED, not laser. Here's what I've got going on.

I have already installed a magnetic door locking device, which holds the door closed while power is applied. For entering from outside I'm using an RFID reader, which I've already successfully interfaced with my PIC. For the interior I need a mechanism to let people out (they could scan their RFID tag from the inside too, but that would not fly for fire safety).

Basically I have three options.
1 is a mechanical switch of some kind. That would require replacing the existing push bar or fitting some sort of switch bar to it. That would require the most work and fooling around.

2 is a capacitive touch sensor type setup. I would have to put some metal strips on the push bar that are insulated from the bar itself, because the bar, door and building are all metal. I did some basic research and found different designs for capacitive touch sensors, but I don't know which would work best for this, nor how they would work if someone was wearing gloves or leaned against the push bar with their body. I have seen one of these "exit devices" pre-made that is touch sensitive, exactly for this application, but it was several hundred dollars.

3 is what I'm going with, which is to shoot a beam across the entire width of the door opening (double doors, around 5 feet or so total) right across where the push bars are, and pretty much as close to the bars as I can get. Now if someone tried to push on the glass to exit, they won't break the beam. But that's okay, because the bars will be labeled "Push to Exit". This will work if someone leans up against the bar too. When the beam is broken I will keep the door unlocked for a few seconds to give them time to actually start opening the door. So I suppose that a regular IR LED would work fine at that short of a distance, and maybe, hopefully, I won't even need lenses.

Dan East

 

[dknguyen]

At my work we just use a doorknob that can only be turned from inside...You could just use a short-range pyroelectric sensor. No need for wiring, messing around with multiple detectors or emitters, or building it into fixtures. Just mount somewhere near the door (or maybe on the door) with an adhesive pad or something.

Honestly though, if it's a fire hazard thing, I don't think any kind of electronically-based exit mechanism is good, especially if there is some power-backup thing going on. One-way doorknob with a card that opens it is the simplest and best thing I think (except you need a door knob).

 

[sam2]

So if it is an unfocused beam, then what is the difference between it and an LED? The intensity? The frequency of the light?

Dan East

A laser diode ( any laser) puts out coherent light(it has a very narrow bandwidth,and its in phase). sam

 

[things]

a 1mw red laser poses no serious risk for momentary viewing, but avoid it anyway. a laser emits one single frequency of light, whereas a led emits several different frequency of light. and as someone has already mentioned it's coherent light, a laser must have coherent light to work. Even lasers's light spreads out, but at a very slow rate. the size of the dot coming out of the laser directly is probably only a couple of mm big, but at 5 meters, it could be over 2cm's big!!

 

[ecerfoglio]

Even lasers's light spreads out, but at a very slow rate.

Semiconductor (Led) lasers allways diverge, because the "mirrors" are the crystal's faces and so are plane.

Non-semiconductor lasers (gas, dye, solid rod, etc) have external mirrors, which are often concave so the beam does not diverge.