# Laser light with 100 meter range with continuous blow capacity of 12 hours at night

#### jivans

Joined Oct 16, 2019
4
Hi Community,
I've some queries regarding laser light, can you please guide me?
#1: I want to make laser light with 100 meter range, what will be approx cost of that laser nosal?
#2: will it damage if I blow continue for 12 hours?
#3: what battery may I need to use so it will blow for 12 hours continuously?
note: I do not have idea, so you can suggest laser specification.
Thank you

#### Yaakov

Joined Jan 27, 2019
1,612
Welcome to AAC.

What does this laser have to do at 100m? The idea of "range" doesn't really mean anything without specification.

#### jivans

Joined Oct 16, 2019
4
Hi Yaakov,
My purpose is make laser light security in farm. At other end I'll setup LDR.

#### Yaakov

Joined Jan 27, 2019
1,612
Hi Yaakov,
My purpose is make laser light security in farm. At other end I'll setup LDR.
I suspect that using a retroreflective scheme where you use a reflector at the far point to return the light to the detector would save a lot of trouble. It would allow you to power the laser without a battery, and make alignment far easier.

#### jivans

Joined Oct 16, 2019
4
I suspect that using a retroreflective scheme where you use a reflector at the far point to return the light to the detector would save a lot of trouble. It would allow you to power the laser without a battery, and make alignment far easier.
sorry, I'm not getting you exactly. even without LDR at other point just laser((light beam) will help us to protect crop from animals.

#### Yaakov

Joined Jan 27, 2019
1,612
This is the basic idea. Everything active is on one end. No battery power is necessary and since the reflector is a retroreflector alignment is greatly simplified. The retroreflector returns light at the angle of incidence, you just have to hit it.

There are many laser diode modules that could do this, and if you modulate the light and possibly (color) filter it, you can reduce false operation.

#### jivans

Joined Oct 16, 2019
4
This is the basic idea. Everything active is on one end. No battery power is necessary and since the reflector is a retroreflector alignment is greatly simplified. The retroreflector returns light at the angle of incidence, you just have to hit it.

There are many laser diode modules that could do this, and if you modulate the light and possibly (color) filter it, you can reduce false operation.

Thank you very much!

#### MisterBill2

Joined Jan 23, 2018
7,283
A really neat trick for both modulating the beam and detecting it without the possibility of other light being a problem was used in an old Radio Shack intrusion alarm device. It used a stereo decoder IC to generate the frequency, and the stereo detect signal to detect the presence of the reflected light beam. AN LDR will never be fast enough or sensitive enough, instead use a phototransistor. At 300 feet or so you will need amplifiers both to drive the laser device and to boost the returned signal. One source of good lasers is found at the "laser66" website. But you will need to call their number because they are not good at answering emails.

#### oz93666

Joined Sep 7, 2010
737
There is always beam divergence with a laser ... The light will start out at less than 1mm dia ...at 10meters it will be about 1cm dia ... at 100m about 10cm dia ( this is from a $10 laser , around a few 100mW) .... This divergence is no problem , it will still be bright enough , and will make aiming easier ... In addition you can have a sensor which is specific to the light you are using which will give more sensitivity ... First thing is to decide on sensor ... this will determine the color of laser ... power of around 200mW should do the job and not consume much power ....eBay Yakkov's idea of having the source and detector at the same location will make life easier .. if you can't obtain a retroflector , a mirror will do , but will have to be fixed on a very solid post (no wobble in the wind) ... There is the problem of moths breaking the beam ... Last edited: #### djsfantasi Joined Apr 11, 2010 6,957 Or dogs, cats, raccoon, skunk. fox, coyote, etc, etc, etc... #### oz93666 Joined Sep 7, 2010 737 Or dogs, cats, raccoon, skunk. fox, coyote, etc, etc, etc... lol ...Yes ...I guess you just have to select height so small animals can pass underneath ... Would be OK as an elephant alarm (many of these causing farmers trouble where I am (Thailand)) .... I think you would need a capacitor across the sensor so if a wind bourn leaf or moth broke the beam for a few msec it would not alarm.... Edit ... Just realized ...you cannot accurately set height unless the ground is perfectly level , very unlikely ... the beam is perfectly straight , at one point it will be 50cm above ground , else where 1meter or more .... I suspect this idea is unrealistic .....Except for elephants! Last edited: #### Yaakov Joined Jan 27, 2019 1,612 There is always beam divergence with a laser ... The light will start out at less than 1mm dia ...at 10meters it will be about 1cm dia ... at 100m about 10cm dia ( this is from a$10 laser , around a few 100mW) .... This divergence is no problem , it will still be bright enough , and will make aiming easier ...

In addition you can have a sensor which is specific to the light you are using which will give more sensitivity ...

First thing is to decide on sensor ... this will determine the color of laser ... power of around 200mW should do the job and not consume much power ....eBay

Yakkov's idea of having the source and detector at the same location will make life easier .. if you can't obtain a retroflector , a mirror will do , but will have to be fixed on a very solid post (no wobble in the wind) ...

There is the problem of moths breaking the beam ...
Retroreflectors are cheap and readily available, fortunately. Trying to use a mirror over that distance would be an exercise in frustration.

#### MisterBill2

Joined Jan 23, 2018
7,283
Depending on the type of animal, the time the beam is broken will vary widely. And a laser with a 100 milliwatt beam is not eye-safe. At 200 milliwatts it is easily able to do serious eye damage to humans. So perhaps there needs to be additional consideration given to the power level. The other consideration is that while a retro-reflector makes it a lot easier, it immediately doubles the distance. Protecting a field means that after detectim
n some action must be taken, and if the action is other than noise or light it probably requires human involvement.
In many areas electrically charged fences are used, with the benefit that they can keep a constant height above ground level. The same fencing can be used for detection by using an electrical field disturbance sensor instead of a high voltage source. A benefit is that small disturbances such as moths or leaves will not be a problem. But a sensor wire would not survive even a small elephant or water buffalo, so that could be a problem also.