Have been asked to pertake in Laser trip wire project

BShanahan14rulz · Feb 24, 2014

Keep in mind that the entire laser probably doesn't have to hit the photocell. It just needs to see enough photons to trigger the device to say "Yes, I see light!"

If by design, the laser emitter and photodiode will be facing each other, i.e. beam will be entering photodiode at a 90* angle, you could make use of reflector to increase the sensor target size. Just like how it can take light emitted from a point and turn it into a bunch of parallel rays, it can take a bunch of parallel rays and focus them down to a point.

Javalin's news is very good, it would seem that you can use prebuilt 12mm modules with some very good reliability, and it sounds like they may be able to go as far as you need them.

Javalin · Feb 25, 2014

Dang, I thought I had a bunch more laying around than I do. I only have 5 of those and 7 of slightly larger ones. (Slightly larger but still very cheap) I was going to offer to send them your way but I don't have enough to fill your requirement.

irishluck · Feb 25, 2014

Javalin said:
Dang, I thought I had a bunch more laying around than I do. I only have 5 of those and 7 of slightly larger ones. (Slightly larger but still very cheap) I was going to offer to send them your way but I don't have enough to fill your requirement.

I appreciate the thought, but no worries there

Ive got a handheld 638nm 500mw laser I built not to long ago that I can use to just test the unit.

But I did look up those ML101U29 lasers again that is on eBay for $29 for 10 diodes.
I tried to find some more information on them and found a site that claims that each diode is good for 10,000 hours which is awesome!

But the beams are pretty powerful. There a 300-400mw beam I do believe. Ill just need to be careful using these. Will have to install some caution signs or something just for protection.

BShanahan14rulz · Feb 26, 2014

You can use a machine gun to drill holes to mount these with, too! Just make sure to put up a sign that says "Please do not get shot by this gun," that should be safe enough.

irishluck · Feb 27, 2014

BShanahan14rulz said:
You can use a machine gun to drill holes to mount these with, too! Just make sure to put up a sign that says "Please do not get shot by this gun," that should be safe enough.

Ha ya.

Hey, would anyone know of some type of connecter that would allow a quick disconnect for a laser?

I would like to design this system to be able to swap out a laser diode and module with ease. Something that could be as easy as just a twist or unscrewing the module.

Any thought? Ive been trying to Google key words to try and locate something but so far no go.

The Lightning Stalker · Feb 27, 2014

Break the base off a light bulb and get a bulb socket. Don't forget to use bulb grease to prevent corrosion.

Javalin · Feb 27, 2014

One concern I would have with a hot swap option is that the drivers can build up a charge when no load is present, then when the new diode is connected a spike can kill the diode on contact. Would you be swapping diode and drivers or just the diode? One solution would be to kill power to the driver, let it discharge then connect the new diode. But your average end user isn't going to be able to do all of that unless the discharge was a "reset" button that would short the driver of course doing this while the system is in operation would likely kill the diode...

irishluck · Feb 27, 2014

Javalin said:
One concern I would have with a hot swap option is that the drivers can build up a charge when no load is present, then when the new diode is connected a spike can kill the diode on contact. Would you be swapping diode and drivers or just the diode? One solution would be to kill power to the driver, let it discharge then connect the new diode. But your average end user isn't going to be able to do all of that unless the discharge was a "reset" button that would short the driver of course doing this while the system is in operation would likely kill the diode...

Well power would be killed to that box before a diode is replaced. I understand your concern with that and I see where your coming from.

I would like the diode and driver to be hot swappable. So if either one goes out, its easily replaced by someone who doesn't know electronics as well.

But power would be killed to the box before anything was worked on or replaced. That should be enough right? I mean that's the same concept that happens in a handheld laser.

Turn the power off by the button to change batteries or driver or diode.
I mean if I had to I could put a discharge resistor on it.

The Lightning Stalker · Feb 27, 2014

Yeah, I agree. And what if the diode failed open circuit? It's a rare condition, but it could happen.

Javalin · Feb 27, 2014

That's a good point I didn't consider a diode failing open since it hasn't happened to me yet but in the instance that it does you'd have to have a way to discharge the driver.

You could have a male connector on the diode and the driver wired to the female end on a board with the discharge circuit (maybe a relay?) between the driver and the female connector. Then it would be plug and play for the end user.

They also have aixiz module holders that look like tiny mic stands. Never used them myself but it would give you a set position but allow for adjustments if needed (although I'm not sure if you'd want the end user to be making adjustments) but not every beam exits the aperture at the same angle.

irishluck · Feb 27, 2014

So if the diode was to fail open then it could short out the driver as well?

I dont see how just a relay would fix that though?

Javalin · Feb 27, 2014

The damage isn't done to the driver, but the next diode that you connect to that driver. Drivers have capacitors that under "normal" circumstances protect diodes from spikes from the charge on the batteries. However if you take the load off the driver those capacitors build up an excess charge and will fry the next diode that you hook up, even if you've disconnected power since the charge was built the instant the diode failed open.

In handhelds it's rare that they fail open, but the can so as a safety measure I as well as a lot of people on LPF make it common practice to short the leads of the driver before hooking it up to the diode.

irishluck · Feb 28, 2014

Javalin said:
The damage isn't done to the driver, but the next diode that you connect to that driver. Drivers have capacitors that under "normal" circumstances protect diodes from spikes from the charge on the batteries. However if you take the load off the driver those capacitors build up an excess charge and will fry the next diode that you hook up, even if you've disconnected power since the charge was built the instant the diode failed open.

In handhelds it's rare that they fail open, but the can so as a safety measure I as well as a lot of people on LPF make it common practice to short the leads of the driver before hooking it up to the diode.

Hm well guess I could just get a resistor or cap to discharge it each time it is disconnected.

Unless anyone knows how to quickly build a board that I can incorporate into the system that is pretty cheap to do.

The Lightning Stalker · Feb 28, 2014

2pcs Adjustable Current Laser Diode Driver 80 500mA w TTL | eBay

42811d1376589366-do-these-parts-make-laser-ld-driver-board-1.jpg

42812d1376589366-do-these-parts-make-laser-ld-driver-board-2.jpg

irishluck · Mar 1, 2014

Well I already have a driver and the max input on the driver that you listed about is 10v. Im using a 12v system.

irishluck · Apr 4, 2014

If im using a 850ma driver, what type of resistor or capacitor would I need to run parallel with the driver to discharge it?

Have been asked to pertake in Laser trip wire project

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