I was trying to read up on IR lasers, do they have the same characteristics of visible beam lasers? Is the beam length about the same with little or no diffusion? Would they be suitable for an IR detector diode? What do you all think?

 

We would still need to be at 125 ft, in direct sunlight.

You are probably going to have to invest in a much more powerful laser for your original circuit to work "without jitter" at that distance....... Even for those garage door IR sensor pairs, I am sure they are limited to a much closer range.....

 

this is what your current circuit would look like if we tried it with an amplifier....





I have not built it yet to try it, I may get some time to play with it this weekend.....


I will also be trying it with multiple CDS sensors wired to provide an "OR" logic, so if 1 OR another is lit by laser it will still function the same.... hopefully, make a better target to aim at from 125 feet....

B . Morse

 

Hello,

Why not use a real comparator in stead of the 741 wich is an opamp?
The LM311 will perform much better.

Greetings,
Bertus

 

I'm coming in late here, but I have to say I'm skeptical about using a laser in this application.

First, the laser has a very small beam, so it has to be carefully aimed so as to hit the detector. If either side of the link gets accidentally moved, it stops working.

Second, is this thing safe around children, and even if it actually is safe, will there be a problem with acceptance by parents? Although maybe with kids playing with laser pointers, small lasers are now seen as pretty safe.

If you're contemplating an IR laser, how will you ever set the system up? At least with a visible-light system, you can aim the red dot at the sensor and know when it's aligned. But an invisible light beam? Good luck.

My suggestion is a pulsating LED (at 38 or 40 KHz) and a receiver like the ones used in TV remote controls. The aiming doesn't have to be super precise and there's no question that the light beam is safe. Agreed, there would need to be some circuit design done at both ends of the link--but if you want good stuff, you have to work for it.

But now I see what I'd skipped over before--125ft range. TV remote controls aren't designed for that! You'd need quite a bit of optical power to trigger the detector at that distance, so maybe the laser is the way to go. But by the same token, aiming the laser would be very exacting; a tiny change in angle and you'd lose the light spot. This isn't easy.

 

My suggestion is a pulsating LED (at 38 or 40 KHz) and a receiver like the ones used in TV remote controls. The aiming doesn't have to be super precise and there's no question that the light beam is safe. Agreed, there would need to be some circuit design done at both ends of the link--but if you want good stuff, you have to work for it.

You do realize that the op has 125 feet or air space to cover, in broad daylight, so I would like to see a modulated IR system that can reach that far and be stable with sunlight, that can be built at minimal cost.......

 

Hello,

Why not use a real comparator in stead of the 741 wich is an opamp?
The LM311 will perform much better.

Greetings,
Bertus

Thanks Bertus.....
I was just trying to use what I have on hand, and the 741 part of the circuit is from Forest Mims III's mini engineering notebook in optoelectronics..which he is using as a CDS amplifier.... I just thought I would try it out, but I could use a comparator such as the LM339 which I do have some on hand....

 

Ypu guys are way ahead of me, but whatever you think will work is good with me. I will try to put it together, just give me a parts list and a layout of what you think and I'm there.

 

Ypu guys are way ahead of me, but whatever you think will work is good with me. I will try to put it together, just give me a parts list and a layout of what you think and I'm there.

I am definitely going to be working on a couple of different circuits this weekend for you, I do not like leaving anything unfinished or not working to specs..... so I will definitely be on this till the end...... If I have to design and build something then ship it out to you to get this done, then that's what I will do...


BTW, where did you get your green laser pointer from and how much was it?? (In case I have to get one to modify for a pulse modulated long range laser transmitter/receiver pair).....
B. Morse

 

And in reply John P's question of safety, Here is some perspective. I have a seven year old son, running an 1100 pound horse at more than 30 mph straight at a crowd of people behind a flimsy wood rail, and then trying to make him turn around a barrel from a dead run. I don't think this group of cowboys isn't going to be too worried about a laser level aimed at a target. As far as aiming, that is why a garage door detector would be handy, the LEDs on the side light up when you are correctly aimed. I am sure a curcuit could be built with some type of signal when the beam is aimed correctly. My laser level has a simple sighting device along the spine of the body, you can get very close with that. I would probably try to change the diode in the laser level to an IR diode if you think that would work, because the frame and set-up works so well for what I want it to do. Thanks again for all your help

 

You e-mail me an address and I will send you the one I have. But you were correct in the estimation that the red laser would work better with the CdS. I get a more stable performance from the red laser from my david white laser level than I do from the higher power green laser. (The green laser pointer was an E-Bay purchase, $7.99 with free shipping, but took three weeks to get from Hong Kong)You let me know what you need, this is a fun project that is filling up my long cold winter (This is the snowiest, coolest winter I remember in recent history, It looks like the UP around here

 

Would something like this detect a visible beam laser

http://cgi.ebay.com/ebaymotors/Esco...2aQQitemZ320493775402QQptZCarQ5fAudioQ5fVideo

 

I will just use a red laser then, I have plenty of red laser diodes laying around I can play with... I am basically thinking of creating a frequency modulated laser transmitter and a matching receiver, so it will be 2 separate circuits if anything. I also have some PIN photodiodes that I salvaged from some laser barcode scanners that I might use for the sensor, since these are used in the manner we need anyway, which is detecting laser light, so it should be more suitable than CDS, but I will still play with the CDS setup also.... have not given up on it yet...

 

Hello,

I think not. It is to detect the laser of the speedgunn of the police and the radarsignals for speedmeasurement.
This is not allowed to usen in holland and some more european countries.

Greetings,
Bertus

 

Otherwise, this could be an option, I would just need to know how to output the same switch curcuit from the detector to make the timer work
http://cgi.ebay.com/JOHNSON-AccuLin...emQQptZLH_DefaultDomain_0?hash=item3efd319c6a

 

PIN photodiodes were what I was inquiring about before? (the little sensors with the lens attached?) My rotary laser detector beeps faster and faster until the laser is in the "sweet spot" then goes to a continuous tone, and displays the line in the lcd screen (don't want to part that one out or hack that one though, part of my DeWalt set) Do you remember the earlier post about hacking into a cheap stopwatch and soldering leads to the start/stop switch for external inputs? Has anyone ever tried this? I ordered a $3.99 stopwatch to attempt this, so I could make a unit for testing and not use my timer I built (Hobby engineering kit H01256-01A and H01736-01B)

 

this is the pin diode I will be using, it already has the lens on it to filter out everything except the red laser..... and also a high output red laser module.... and the lens / light collector for the pin diode....

looks like I am burning some cataracts off this weekend!

I also have a HeNe Laser, but I don't think the horses would like that too much....

 

Note that I edited my previous message to note the distance required one minute before BMorse's message pointing it out!

I did a web search on "Long distance IR link" and came up with this site where they talk about ranges of 100ft. Allowing for the fact that this is a sales pitch where they say "up to" 100ft which probably mean actual ranges of far less, at least someone is talking about distances of that order of magnitude. It may not be a wild fantasy.

http://www.rentron.com/remote_control/TINY-IR2.htm

CdS sensors have the reputation of being quite slow, so if milliseconds are an issue, you might want to check the response time from light to dark.

And if the laser turns out to be a little too powerful for detection purposes, you could always use it for branding the horses instead.

 

Actually, the preferred method of Identification for horses is now TATOOing on their inside lip, BMorse can probably take care of that for me too. (Some nice work by the way, is it a lot of custom designs?) But it may make the horses run a little faster to heat them up quick as they run through, HMM, there a thought for the super laser!!

 

In testing with the CdS sensor, you can get a response by flashing you hand across the beam about as fast as you can swing it, so a 60" long horse should break the beam adequately for the start and stop signals. As long as the response time doesn't change from each trigger set, it doesn't matter, and if we are within a hundredth or so, thats close enough.