Welcome to Laser Pointer Forums - discuss green laser pointers, blue laser pointers, and all types of lasers

Buy Site Supporter Role (remove some ads) | LPF Donations

Links below open in new window

FrozenGate by Avery

Laser Tripwire Project






I was experimenting with these LEDs i had and I was trying to get a voltage reading from them by pointing a 1mW laser pointer at it and I wasn't noticing a difference, I am also using an analog multimeter...
Is the voltage difference really small?

Then, i decided to use a 30mW green laser with a green LED and I got about a .2 V reading out of the diode...
not sure if 1mW is just not enough power or if the red LED isn't that good with the laser i was using,
I hope the 5mW laser i just purchased will suffice (assuming i use an LED as my detector)
 
Last edited:
I just verified a 1mW RED Laser that in fact it was 1mW...
I used a Small Red LED at 12" and I got a voltage of about
1.4 Volts .
I tried a larger Red LED with the same results... I used a DMM

I also did the test with a tested 8mW RED Laser with the same
results as well.

Maybe your LED is damaged or your Analog meter is loading
the LED... My RED LEDs only produce about 5-8 MicroAmps of
current so it's quite easy to load them...


Jerry
 
Last edited:
lasersbee said:
Sorry for the double post but the last post was long enough...IMO..

Here is a circuit that I put together and tested this morning...
It works well with a 5mW red pointer at a distance of up to 25 feet
in the shop light environment...

I first used a Solar cell from a $1.00 calculator with the identical
circuit... but it required some small amount of ambient light
shading..

I then tried an old trick of using a large T1 Red LED as the detector...
and that provided enough ambient light elimination that it worked
under the shop lighting as well as movable local work light without
extra shading...

I added a CD4584 Schmitt trigger buffer to make sure the output
signal transitions cleanly without chatter while the Laser beam was
at the level switching threshold..

To interface that circuit to the outside world you can easily drive
the LED in an optoisolator from the Schmitt buffer's output.


Jerry
Click to expand...

Hmm i'm confused. " T1 Red LED as the detector "?
Is... that meant to be a driver circuit for the LED? Or is that suppose to be the sensor circuit? I'm confused as to how a LED can work as a detector? Is this the photodiode your talking about?

Edit: Nevermind, was reading above posts.... Shinning a LED at another LED will generate a voltage? Interesting. I still don't see how the output will lock based upon a interruption in the diode voltage output. However, that would be a cooler way to do it than using a photoresistor.
 
Last edited:
random person said:
Hmm i'm confused. " T1 Red LED as the detector "?

Edit: Nevermind, was reading above posts.... Shinning a LED at another LED will generate a voltage? Interesting. I still don't see how the output will lock based upon a interruption in the diode voltage output. However, that would be a cooler way to do it than using a photoresistor.
Click to expand...


Yes.....

Sorry.....:yabbem:
I have no idea what you are trying to say or to what you are
referring to about output locking.....:thinking:

Jerry
 
I believe hes referring to the idea that, once you set the alarm off it still set off until it is reset.
 
Last edited:
Thats pretty cool, I used a DMM and I got a 1.6 V read using the green LED with my 30mW laser, I only got a .4 V read from my 1mW red laser on the red LED but this might be because the batteries appear to be dying in the laser, the intensity of the beam is low, etc. I am going to try and design circuits for use with either an LED photosensor, or with a CdS photosensor, and I will do some tests when my 5mW laser comes in and decide which one i want to use.

EDIT: I used a red LED flashlight on the LED and it got 1.2 V outs of the LED
I am still not sure if I am going with an LED detector or a CdS one though.
 
Last edited:
AbsoluteZedo said:
I believe hes referring to the idea that, once you set the alarm off it still set off until it is reset.
Click to expand...

Yeah... that's what I posted above about how the circuit functions
that R_P posted...

But what is he trying to say or ask...:thinking:

The Red LED has a built in Filter... The red plastic casing
filters out a lot of ambient light besides RED.. That's why
I chose it for your RED Laser.

The CdS cell will require a filter and/or shading from ambient
light...


Jerry
 
Last edited:
random person said:
Hmm i'm confused. " T1 Red LED as the detector "?
Is... that meant to be a driver circuit for the LED? Or is that suppose to be the sensor circuit? I'm confused as to how a LED can work as a detector? Is this the photodiode your talking about?

Edit: Nevermind, was reading above posts.... Shinning a LED at another LED will generate a voltage? Interesting. I still don't see how the output will lock based upon a interruption in the diode voltage output. However, that would be a cooler way to do it than using a photoresistor.
Click to expand...

If you ever need a bi-directional optoisolator, this is also pretty much the only way to make one (nobody makes them commercially) You just put two LED's face to face and epoxy them together with transparent epoxy then seal the whole thing up so it's light-tight.
 
Last edited:
lasersbee said:
Yeah... that's what I posted above about how the circuit functions
that R_P posted...
Click to expand...

Ahh... I thought you were imply that your bjt circuit would "latch... or lock the output or... stay active high/low.. or whatever you want to call it. I was thinking theres no way a single BJT/Fet and some resistors can do that. .. thats why I was confused.

But what is he trying to say or ask...:thinking:
Click to expand...

I was attempting to baffle you into surrender so I could take over your LPM business in your leave of absence from sanity. :na:
 
Why not use a photoelectric switch? will do the same thing....I use them all the time at work for when people enter a restricted area and shut a machine down.
 
Fiddy said:
Why not use a photoelectric switch? will do the same thing....I use them all the time at work for when people enter a restricted area and shut a machine down.
Click to expand...

Industrial Photoelectric switches a very expensive (>$100.00)
The member seeking help in the 1st post requires a cheap
solution... If you read the other posts you will see that even
red 5mW Laser is almost busting his budget...:beer:

Jerry
 
random person said:
Shinning a LED at another LED will generate a voltage? Interesting.
Click to expand...

It works fairly well. If you connect and oldfashioned green and yellow led to eachother, you can light up the yellow by shining a green laser into the green LED. Its not mighty efficient, but a good proof of principle :)
 
You must log in or register to reply here.





Back
Top