I'm pondering the possibility of using an IR receiver in the targets for my laser target rifle "toy"
My proof of concept is working as intended. I "shoot" 50 ms pulses from a red laser pointer (<1mw). The target is an LDR looking for increases in light.
But I have to calibrate to background lighting, and stray light will register as a hit.
But I wonder if it is possible to modulate a green laser pointer to 38 kHz?
Green laser pointers are infamous for having a rather large amount of IR in the beam, especially the cheap ones, meaning that they should be plenty enough for activating the receiver.
They are based on an IR laser, and frequency doubling gives the green laser. But plenty of IR gets through in the beam.
In higher output green lasers that is a real hazard, but in the low power pointers, it is consider to be a minor problem. The strong visible light will make you close your eye before it is damaged.
If the beam can be modulated, the receiver will be a sensitive target, but insensitive to interference.
(And you could build a remote with a 300m range.... Whatever that should be used for)
IR receivers are tuned around 940nm wavelength (+/-). You would be very fortunate if the emitted IR wavelength matched. So I would be surprised if you achieved range @ whatever wavelength of IR came from the Laser .
A better way to get range is to use optics and just standard IR Leds. (read up on Lasertag)
PS: don't take risks with IR/Lasers & eyes = no second chances. With IR you wont know the damage is done until blind, because the eye doesn't react to invisible IR as it does with visible light! (normal remotes controls should not be a problem)
I wonder if it is possible to modulate a green laser pointer to 38 kHz?
Yes
Green laser pointers are infamous for having a rather large amount of IR in the beam, especially the cheap ones, meaning that they should be plenty enough for activating the receiver.
No according to :-
The IR used for green is 808 nm, while you can get 850nm IR receivers the normal type is 950nm as they are further into the IR and so suffer less interference from viable light. So the IR from a green laser is not so close to the peak sensitivity and so won't be as sensitive, hence as long a range as it could be. How bad it will be can be seen from looking at the appropriate curve in the data sheet of the IR receiver you want to use.
It felt like a good idea, I'm glad I could ask you before trying.
800nm is just at the "too little to be worth the effort" sensitivity.
IR LEDs are out of the question.
I need the pin point spot from the laser for the "rifle" to be of any value for training.
I guess it is back to the LDR.
It works perfectly well the length of my house. I'll start out by improving the current version
Kongsberg, Anschütz and Röhm make training systems, but they cost more than a real rifle.
The Röhm uses a red laser, I do not know about the other two.
Edit:
Of course, it should be possible to modulate, or even code, the present red laser. Then use a photodiode instead of the LDR, and code the micro-controller of the target to only reacting to the correctly looking light pulses.
You could also use two lasers... One IR and one green... The green for visibility and the IR one for 'contact'. 38 KHz modulation would allow for discerning who hit the target first and total hits too.
Docedison:
You could also use two lasers... One IR and one green... The green for visibility and the IR one for 'contact'. 38 KHz modulation would allow for discerning who hit the target first and total hits too.
Doc
Indeed.
And if the IR was constant on, it would allow tracking of the movements up to, and after the shot. The shot itself could be modulated and coded.
Two laser would increase another problem, that of parallax.
It is bad enough to adjust the scope and a visible laser to hit the same point, but adding an invisible laser that must be made to hit the same spot as the other two, would require quite a bit more with regards to adjustable mounting of the lasers.
It was an obvious solution to buy laser sights, but unfortunately they are restricted in Denmark.
(Legislators should not be allowed to go to the movies!
On the other hand, they've just lifted the ban on silencers due to concerns for the shooters hearing and noise pollution)
I try to keep it simple, and I will make a post about the system once I've given it a make over. For the moment it is simply a piece of 2x4 mounted with scope, laser, handle, batteries and electronics.
How small is the active target? and over what range do you intend to have the "Rifle" be accurate?
I would think that IF the target was larger than the parallax... the parallax would disappear over some usable range.
Much like 'sighting' in a rifle
Calibrating the 'rifle' sights @ 100 meters and then trying to use the 'rifle' @ 1 km cannot work... well, if at all..
It would appear that you have little experience with the project you are trying to solve.
My advice would be to create a set of conditions or limits where the device must be accurate and calibrate the device within those limits..
There is an old maxim that is most necessary... "Plan your work and work your plan"
BOTH actions are a requirement to complete ANY task.
Attempting to build an "Anything" device is clearly unspecified and will fail... No accurate specifications = no accurate device.
A Vishay TSSP4038 will work with a red laser. No idea if it will work with green. Just a cheapo laser pointer and tested at ~40' (~12m) -- the length of my house
I'm surprised you got a good signal using an LDR. From my experience the modulation was undetectable at 38KHz.
On the prototype, the scope is from an old German PzF-44.
That means I have a graduated reticle, and as long as it is aligned vertically, the horisontal parallax is taken care of by choosing the correct aiming point in the reticle.
If the range was fixed, a regular sighting in of the scope would be possible.
(But I think it would be more fun with a "mil dot reticle". Then the center could be adjusted for "infinity", and correction on shorter distances could be done by the dots)
The present target is 20 mm in diameter, which is relevant for my typical indoor distances from 5-20 meters.
From a free standing position, I want more than 90% hits on a 20mm circle at 10m distance (and no misses when prone).
I do not code or modulate the pulses yet. It is just a "straight" 50 ms pulse. Neither does the target do any decoding, it just checks for "enough value above ambient", and declares that to be a hit by flashing an LED.
Very interesting about the Vishay TSSP4038.
Will it register on direct hits only, or can it see reflections from other surfaces? In other words, could the target be a 20cm matte plastic disc, with the receiver looking at it from the back side?
Peter_I:
Will it register on direct hits only, or can it see reflections from other surfaces? In other words, could the target be a 20cm matte plastic disc, with the receiver looking at it from the back side?
It's going to come down to the strength of the laser required and what you're using to diffuse the light. The easier solution would be to just "unfocus" the laser so you get a larger spot.
Something I toyed with was aiming the (modulated) laser at a 6V solar panel. The panel output was connected to an IR LED which was then pointed at the IR receiver. It certainly does work, but obviously there are problems with direct sunlight hitting the solar panel and popping the IR LED with too much current. I only tested it indoors -- I'm sure there are plenty of hurdles getting it to work in bright sun. But it does give you some idea just how sensitive these IR receivers are since that IR LED couldn't have been fluctuating much at all.
Peter_I:
Will it register on direct hits only, or can it see reflections from other surfaces? In other words, could the target be a 20cm matte plastic disc, with the receiver looking at it from the back side?
It's going to come down to the strength of the laser required and what you're using to diffuse the light. The easier solution would be to just "unfocus" the laser so you get a larger spot.
Something I toyed with was aiming the (modulated) laser at a 6V solar panel. The panel output was connected to an IR LED which was then pointed at the IR receiver. It certainly does work, but obviously there are problems with direct sunlight hitting the solar panel and popping the IR LED with too much current. I only tested it indoors -- I'm sure there are plenty of hurdles getting it to work in bright sun. But it does give you some idea just how sensitive these IR receivers are since that IR LED couldn't have been fluctuating much at all.
I have no doubt, that they are very sensitive.
You can point the remote away from the receiver, and it will see the signals perfectly well, just from the reflection on the walls.
In your test, you used an IR-LED to transmit the signals, so it was in the right wavelength (or at least in the ball park).
the really interesting part is, if the laser can do anything about it.
The plot of sensitivity does not look too good for a 650 nm red laser.
I guess that direct hits cause some IR from the plastic or that a bit of light gets through.
I know what you mean by the sensitivity of the receiver to a red laser; that graph has been discussed before. It would be interesting to know why it works.
You can get 1um LASER diodes for fairly reasonable prices. you'll need a collimating lense and a 2.2V 80-100mA driver. It'll fire a p4038 just fine if moduleate at 36-38 KHz. You use a paper or plastic tube about 25mm long and maybe 10mm in diameter to reduce the possibility of near hits firing the sensor.
You do NOT want a visible (green, or to some extent red) coaxial LASER in your sender for training. That just trains the subject to follow the beam into the bulls eye. You indicate hits by a monostable driven LED at the target. Unless you want to show near hits and misses for targeting correction, then you are talking about a martix of sensors and lots more money (and something bigger than an UNO to detect and register the hits).
It's a fun project, but for practicality, there are cheaper units available on the market that use RED lasers at closer range.
But, if you decide to go ahead with it, GO FOR IT, LEARN, and Have Fun!
