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Topic: Fast laser switching. (Read 2060 times) previous topic - next topic

joehleonard

I am wondering how "fast" I could switch off a laser.

I already have another post with some information in it, how ever this is something that is slightly different from that all though it has to do with the same topic.

Let's say for instance I had an arduino, and off this arduino I have a laser diode that is controlled by a mosfet, this laser diode shines on an LDR.

Now let's say that some thing was to break that beam. The LDR would send its signal the arduino that the beam has been broken. Which would I turn trigger the mosfet to turn off.

I will be ordering some parts soon to test this theoretical idea.

But would some one have an idea of how much time this would take?

I was curious about reflectivity, for example if some one were to walk In front of the beam and at it reflected off their clothes into some ones eye. Granted it would be a classification type 3r eye safe laser. So I don't think it would really be an issue but.

Also if some one has a better solution on how I could effectively fast switch the laser off I'm all ears (or in this case eyes)

Just for curiosity sake

AWOL

If fast response is important, I wouldn't be using an LDR.

joehleonard

AWOL, thanks for your input, instead of LDR, what other options are there?

DVDdoug

Quote
I am wondering how "fast" I could switch off a laser.
A basic laser module or an assembled laser can't be switched on & off quickly.  In fact, the power supply will be designed to hold constant current & constant brightness with some variation in power supply voltage.

However, a laser diode can be switched/modulated very fast...  certainly much faster than the Arduino can send/receive data... if you have the right driver circuit...   That's how high-speed broadband fiber optic communications works.

Quote
I have a laser diode that is controlled by a mosfet
I'm not an expert on laser drivers, but it usually takes more than a simple MOSFET.   Here is some information I found.

Quote
... instead of LDR, what other options are there?
A photodiode or phototransistor.

Boardburner2

I am wondering how "fast" I could switch off a laser.

I already have another post with some information in it, how ever this is something that is slightly different from that all though it has to do with the same topic.

Let's say for instance I had an arduino, and off this arduino I have a laser diode that is controlled by a mosfet, this laser diode shines on an LDR.

Now let's say that some thing was to break that beam. The LDR would send its signal the arduino that the beam has been broken. Which would I turn trigger the mosfet to turn off.

I will be ordering some parts soon to test this theoretical idea.

But would some one have an idea of how much time this would take?

I was curious about reflectivity, for example if some one were to walk In front of the beam and at it reflected off their clothes into some ones eye. Granted it would be a classification type 3r eye safe laser. So I don't think it would really be an issue but.

Also if some one has a better solution on how I could effectively fast switch the laser off I'm all ears (or in this case eyes)

Just for curiosity sake
Are you asking about detection or switching of the light signal.?

An LDR has slow response.


GoForSmoke

AWOL, thanks for your input, instead of LDR, what other options are there?
Phototransistor.

I got laser modules from DX.com that run directly off Uno pins, bag of 10 for about $4 shipped.
I haven't tested for lifetimes but with a fast blink program running one it makes dashed lines when swept across a wall.

I hope that you have a good idea of the potential hazard that even reflected laser can have. You don't want to wind up in court trying to explain negligence. One of my buddies was swinging a pointer around his den and it caught a wide-angle mirror. The little bit he got had one eye seeing red for over an hour.

They're down to $2.99 for 10. 20mA, 4.5V (run on 5V, not tested for lifetime) with constant current driver.

http://www.dx.com/p/12mm-5mw-red-laser-diode-modules-black-dc-4-5v-165078#.VwA7psXKOFQ

1) http://gammon.com.au/blink  <-- tasking Arduino 1-2-3
2) http://gammon.com.au/serial <-- techniques howto
3) http://gammon.com.au/interrupts
Your sketch can sense ongoing process events in time.
Your sketch can make events to control it over time.

aarg

This sounds weird. If you are detecting a break in the beam and then turning off the laser, why not just ignore the detector for a while, after turning the laser off? Why do you need to turn it off quickly?
  ... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

joehleonard

I'm putting together s laser maze. I have done plenty of research and the safety surrounding the laser beams. I'm currently working with the government regulatory office to build this project.

I was unaware of the website dx.com but will check this out tonight.

I will be looking for some class 3r laser beams <10mw and will be using a hazer in the room to illuminate the beams as well.


I have started a different thread on the inner workings of the unit, I was however just curious about the switching and how fast they would actually be able to switch.

I understand it does sound weird but what eill happen is, the laser will shine on the LDR or the phototransistor and will signal the arduino as soon as there is s break in the beam. It will than disable that beam for a timed period before it comes back on.

Also the reason I would like the laser to rapidly turn off is more of a safety feature than anything. As I said they're eye safe lasers that I will be using.

Thanks for all your suggestions

TomGeorge

Hi,
Interesting article.

http://www.ti.com/lit/ml/ssqw095/ssqw095.pdf

Have you tried googling     laser diode driver

Hope it helps.. Tom.. :)
Everything runs on smoke, let the smoke out, it stops running....

GoForSmoke

The ones I have are more than fast enough for that. I just dunno their lifetime/MTBF.
Those are 5mW.

I think you will keep your thing safe though maybe during development get yourself a pair of real laser tag goggles. They do or did exist.

While you're doing this, take a ballpoint pen and screw the front barrel off, the part that narrows to a small hole and stick a regular 5mm led in the back. Power it up (through the right resistor) and see what kind of beam that gives with 20mA running through it... just for fun, the laser will look cooler.

My fun with lasers is making interference patterns and lines on blank walls. I haven't got a hologram to view with one, don't see much of that and after seeing what's involved I can guess why.   
1) http://gammon.com.au/blink  <-- tasking Arduino 1-2-3
2) http://gammon.com.au/serial <-- techniques howto
3) http://gammon.com.au/interrupts
Your sketch can sense ongoing process events in time.
Your sketch can make events to control it over time.

Paul__B

Also the reason I would like the laser to rapidly turn off is more of a safety feature than anything.
They will turn off well within a millisecond.  The cheap ones with no current control (other than a resistor) should in fact be able to be modulated on and off, very fast.  More than fast enough for safety as it will take more than that time for the object to move into the beam to a position where it could strike the eye.

The exception would be glass or transparent plastic (sheet) that would only partially reflect and therefore not shut down your system.

Yes, a photo-transistor, and no LDR involved.

GoForSmoke

The ones I got have a little tiny board with some surface mount parts, more than resistor. That's not saying anything else. For all I know, they're capable of modem speeds, I should dig one out and see if PWM produces a dash pattern when I wave the dot across a wall.
1) http://gammon.com.au/blink  <-- tasking Arduino 1-2-3
2) http://gammon.com.au/serial <-- techniques howto
3) http://gammon.com.au/interrupts
Your sketch can sense ongoing process events in time.
Your sketch can make events to control it over time.

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