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Author Topic: Can we use an IR beam to control LEDs?  (Read 3195 times)

Offline thedoc

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Can we use an IR beam to control LEDs?
« on: 14/06/2012 16:30:01 »
Kevin Auslund  asked the Naked Scientists:
   
I enjoyed your website discussion about infrared.  Would you know if it feasible to turn on an LED light bulb with an infrared ray?  

I am looking for a prototype device to use with an interesting shooting game called Laser Clay Pigeon Shooting. This is a clay disk thrown in the air and a shotgun emits an infrared beam that reflects off the clay target and then through wizardry sets off a sound speaker system shot sound.  However, what I am looking for is the possibility of having the disk itself light up momentarily when it is shot by the beam. (This would be analogous to a traditional clay targets exploding in air when hit by lead pellets. But, this safe version of the game would make the thrown target glow or blink when hit by a beam or, turn off an existing lit disk.)
 
Below is a YouTube on what the game is like.  Maybe the trick is to have the disk continually glow with an LED and when hitting the target with an infrared beam it turns off. Anyway, I would like your opinion since you are a physics and infrared expert. (I realize an LED disk may not show up well on sunny days but perhaps when cloudy or overcast it would be enjoyable to see the disk change color when hit – either turned on or turned off.) I appreciate your opinion on the possibility. With LED technology and a button watch battery I would think something could be developed.
 

 
Kevin Auslund
State of Minnesota, United States

What do you think?
« Last Edit: 14/06/2012 16:30:01 by _system »


 

Offline graham.d

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Re: Can we use an IR beam to control LEDs?
« Reply #1 on: 18/06/2012 12:59:25 »
It is relatively easy to have sensors that detect a short pulse (representing impact from a shot gun pellet) and then activate any electronic feature you may wish, including turning on or off one or more LEDs. This is a feature already used in team shooting games where people carry IR transmitting guns and wear vests with detectors that, when "hit" remove a "life" and temporarily disable your own gun. In a disc (clay pigeon) it would be equally possible although, as these would not be disposable, would require collection and re-use.
 

Offline RD

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Re: Can we use an IR beam to control LEDs?
« Reply #2 on: 18/06/2012 16:58:19 »
... This is a feature already used in team shooting games where people carry IR transmitting guns and wear vests with detectors that, when "hit" remove a "life" and temporarily disable your own gun. In a disc (clay pigeon) it would be equally possible ...

IR sensors can be activated by sunlight, the wobbling motion of a spinning disk could expose it's sensor to pulses of IR from sunlight possibly causing a false positive : score a "hit" when there was none.
Detecting a signature pattern of IR pulses emitted by the gun would reduce the odds of a false positive. 

Quote
a strong infrared source such as from a vehicle headlight or sunlight reflecting from a vehicle window can overload the chip with enough infrared energy to fool the electronics and cause a false alarm.
https://en.wikipedia.org/wiki/Passive_infrared_sensor


NB: IR lasers are not necessarily safe ...

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Infrared lasers are particularly hazardous, since the body's protective "blink reflex" response is triggered only by visible light. For example, some people exposed to high power Nd:YAG laser emitting invisible 1064 nm radiation, may not feel pain or notice immediate damage to their eyesight. A pop or click noise emanating from the eyeball may be the only indication that retinal damage has occurred i.e. the retina was heated to over 100 °C resulting in localized explosive boiling accompanied by the immediate creation of a permanent blind spot
https://en.wikipedia.org/wiki/Laser_safety#Laser_radiation_hazards
« Last Edit: 18/06/2012 17:26:52 by RD »
 

Offline graham.d

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Re: Can we use an IR beam to control LEDs?
« Reply #3 on: 18/06/2012 18:53:01 »
Yes, sending a sequential code of pulses would reduce false hits to a negligible level. A TV remote control works on a similar principle. Before anyone asks, the code sequence can be sent out fast enough so that the disk rotation should not affect the decoding - in any case the sensors would have to be at several points on the disc and the detection would be essentially coherent.
 

Offline graham.d

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Re: Can we use an IR beam to control LEDs?
« Reply #4 on: 18/06/2012 18:55:07 »
I should also add that IR emitters with such codes can be sent out and detected from background at very low levels and well below that which would damage the eye.
 

Offline RD

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Re: Can we use an IR beam to control LEDs?
« Reply #5 on: 19/06/2012 00:27:14 »
I should also add that IR emitters with such codes can be sent out and detected from background at very low levels and well below that which would damage the eye.

The range for clay pigeon shooting is 10x further (100x stronger) than the distance from the TV to it's remote control, and the signal intensity would have to be comparable with IR from sunlight at the clay sensor, so the intensity of the beam from the gun at point-blank range may be sufficient fry ones retina, (particularly as IR is invisible so would not trigger the protective blink reflex).
« Last Edit: 19/06/2012 00:42:34 by RD »
 

Offline CliffordK

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Re: Can we use an IR beam to control LEDs?
« Reply #6 on: 19/06/2012 07:46:33 »
The nice thing about sending code pulses is that one could tell who actually hit the target.

Keep in mind that the pellets in a real shotgun will spread out a bit, whereas a rifle will be extremely precise.

It might be relatively easy top build such a device inside a planetarium.  You would not get the nice open air effect, but one would simply project a spot on the ceiling, and then have the rifles also project a spot on the ceiling.  If they match, then you have a hit.  It could be detected from a central detector.  And, of course, it wouldn't have to be spots, one could project any kind of bird from pigeons to pterodactyls for a more "realistic" experience.  And an IR laser would be just as visible to the right detector as a visible light laser.
 

Offline graham.d

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Re: Can we use an IR beam to control LEDs?
« Reply #7 on: 19/06/2012 12:03:30 »
RD, coded IR pulses (maybe with a pseudo-random code) can be detected at remarkably low levels. Some surveying equipment uses an IR Laser Diode as a transmitter with a PIN diode as a receiver. The IR light is reflected back from a passive station that can be several miles away and can still detect the coded signal and measure the distance to within a centimeter or so. These were used pre-GPS but may now be less used since "differential GPS" is used more extensively. These were not considered a safety hazard as far as I know.

I'm not sure what methods the team shooting systems use (one company was called Quasar - Q-Zar outside the UK), but I'm sure health and safety would have closed them down if there was a risk of eye damage.
 

Offline RD

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Re: Can we use an IR beam to control LEDs?
« Reply #8 on: 19/06/2012 21:21:18 »
I'm not sure what methods the team shooting systems use (one company was called Quasar - Q-Zar outside the UK), but I'm sure health and safety would have closed them down if there was a risk of eye damage.

IIRC that type of laser tag game is indoor so could use low powered IR, not much stronger than a TV remote.

The military version
which is powerful enough to work in sunlight, only avoids retina damage by having a very short pulse duration, and still deserves a warning label ...

Quote
CAUTION label be applied to all laser transmitters.  It should state that invisible laser radiation is present and advise the user not to stare directly into the beam if within three meters of the equipment and not to use optical instruments (such as binoculars) within 20 meters.
http://www.hss.energy.gov/publications/esh_bulletins/BULL0018.html
« Last Edit: 19/06/2012 21:32:00 by RD »
 

Offline evan_au

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Re: Can we use an IR beam to control LEDs?
« Reply #9 on: 20/06/2012 11:20:00 »
Are we thinking about this backwards?

The suggestion was to have the guns transmit a code which is detected by the clay pigeon - which then somehow has to relay a response to the participants; this requires 2-way communications, ie two points of failure.

How about putting the transmitter in the clay pigeon, and the receiver in the rifle, with some sort of indicator to say "hit". This requires only 1-way communication (ie more reliable), and supports multiple shooters - or even the same shooter having multiple shots.
This overcomes the problem of having the laser transmitter in close proximity to the human participants.


However, I can see two potential problems, equally applicable in both cases:
  • You score by aiming directly at the target. However, in real clay pigeon shooting, you would need to point at where the target will be, and allow for the bullet to drop with gravity. Perhaps this is less important with a simulated shotgun than with a simulated rifle.
  • You are taking electronic devices (presumably battery-powered), and firing them far away; then someone has to go and collect them to recycle them.

Note: If the clay pigeon has a flight time of perhaps 5 seconds, it may be better to power it with a capacitor than with a battery - the recharge time is almost instantaneous.
 

Offline CliffordK

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Re: Can we use an IR beam to control LEDs?
« Reply #10 on: 20/06/2012 14:46:13 »
If you are putting all the technology in the gun, then you could simply heat the clay pigeons to a specific temperature, say 100°C.  Then you could simply use stock clay pigeons, then just search for the IR signature in the guns.
 

Offline Geezer

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Re: Can we use an IR beam to control LEDs?
« Reply #11 on: 20/06/2012 21:57:38 »
Why not use IR from the gun to trigger real explosives in the "pigeon"?
 

Offline RD

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Re: Can we use an IR beam to control LEDs?
« Reply #12 on: 20/06/2012 22:40:30 »
Note: If the clay pigeon has a flight time of perhaps 5 seconds, it may be better to power it with a capacitor than with a battery - the recharge time is almost instantaneous.

If they are to be reused having the battery power to bleep/flash would help someone find them.
 

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Re: Can we use an IR beam to control LEDs?
« Reply #12 on: 20/06/2012 22:40:30 »

 

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