# Differentiate between 2 laser beams

hi all,
I am a student studying a microcontroller (8051) course. We are going to desgin a project which is something like a mini shooting game. we use LDR(light dependent resistor) to detect laser beams ( the laser beams are from laser pointers ). When LDR detects the laser, its resistance decrease and voltage across the resistor ,which is in series with the LDR, will increase, so the 8051 can detect the gun shoot from the laser gun.

However, we want to implement a 2-player environment. the LDR have to detect whether player 1 shoot it or player 2 do so. We can't figure out any method to differentiate the 2 laser beams.

My partners came up with an idea that the 2 laser beams from the laser pointers are of different brightness, but I think it doesn't work.
Also, we also thought of connecting a 8051 to the switch of laser pointers, and with a infra-red device which sends back the information to the 8051 (which detects gunshots from LDR) but by using this method, we still don't know which gun shoots the LDR when both guns are switch on together.

any idea to differentiate the 2 laser beams? Should we use other methods to replace laser, like infra-red? because there are several LDR to detect laser, infra -red seems not a good choice because it diffracts too much.

sorry for my poor English!
Thanks everyone!
Samuel

• : hi all,
: I am a student studying a microcontroller (8051) course. We are going to desgin a project which is something like a mini shooting game. we use LDR(light dependent resistor) to detect laser beams ( the laser beams are from laser pointers ). When LDR detects the laser, its resistance decrease and voltage across the resistor ,which is in series with the LDR, will increase, so the 8051 can detect the gun shoot from the laser gun.
:
: However, we want to implement a 2-player environment. the LDR have to detect whether player 1 shoot it or player 2 do so. We can't figure out any method to differentiate the 2 laser beams.
:
: My partners came up with an idea that the 2 laser beams from the laser pointers are of different brightness, but I think it doesn't work.
: Also, we also thought of connecting a 8051 to the switch of laser pointers, and with a infra-red device which sends back the information to the 8051 (which detects gunshots from LDR) but by using this method, we still don't know which gun shoots the LDR when both guns are switch on together.
:
: any idea to differentiate the 2 laser beams? Should we use other methods to replace laser, like infra-red? because there are several LDR to detect laser, infra -red seems not a good choice because it diffracts too much.
:
: sorry for my poor English!
: Thanks everyone!
: Samuel
:

The reason why people use IR is because IR can be modulated to different frequincies.Try using high power IR led's.You can also try to concentrate the emmitter signal-for example-security beams that can work over very long distances.

• : : hi all,
: : I am a student studying a microcontroller (8051) course. We are going to desgin a project which is something like a mini shooting game. we use LDR(light dependent resistor) to detect laser beams ( the laser beams are from laser pointers ). When LDR detects the laser, its resistance decrease and voltage across the resistor ,which is in series with the LDR, will increase, so the 8051 can detect the gun shoot from the laser gun.
: :
: : However, we want to implement a 2-player environment. the LDR have to detect whether player 1 shoot it or player 2 do so. We can't figure out any method to differentiate the 2 laser beams.
: :
: : My partners came up with an idea that the 2 laser beams from the laser pointers are of different brightness, but I think it doesn't work.
: : Also, we also thought of connecting a 8051 to the switch of laser pointers, and with a infra-red device which sends back the information to the 8051 (which detects gunshots from LDR) but by using this method, we still don't know which gun shoots the LDR when both guns are switch on together.
: :
: : any idea to differentiate the 2 laser beams? Should we use other methods to replace laser, like infra-red? because there are several LDR to detect laser, infra -red seems not a good choice because it diffracts too much.
: :
: : sorry for my poor English!
: : Thanks everyone!
: : Samuel
: :
:
: The reason why people use IR is because IR can be modulated to different frequincies.Try using high power IR led's.You can also try to concentrate the emmitter signal-for example-security beams that can work over very long distances.
:
:
:

Hi Samuel,

As you stated before, if you use IR led's you will have problem focusing IR beam because diffraction. You can try switching laser signal (OOK, On Off) at a different frequency for each player. It works in the exact way that IR led's transmitter-receiver does. The only difference except wavelength (Laser: 640 nm, IR: 420 nm approx), is that laser beam is highly coherent, so it doesn't have high attenuation factor by distance.

For each player, you can use a different frequency, through TTL IC's like 74HC14, 74LS04, etc with a couple of components. The ocillator output feeds laser (you can use a transistor for higher power). At the receiver, it's a little bit complex, using two frequency demodulator, each one tuned to freq of one player, and by direct comparition of both outputs, you can determine who shooted.

There is another solution, you can try using two laser of different color (ej: red and green), and a couple receivers (LDR) placed together in the target with color filters.

Good luck
• : : : hi all,
: : : I am a student studying a microcontroller (8051) course. We are going to desgin a project which is something like a mini shooting game. we use LDR(light dependent resistor) to detect laser beams ( the laser beams are from laser pointers ). When LDR detects the laser, its resistance decrease and voltage across the resistor ,which is in series with the LDR, will increase, so the 8051 can detect the gun shoot from the laser gun.
: : :
: : : However, we want to implement a 2-player environment. the LDR have to detect whether player 1 shoot it or player 2 do so. We can't figure out any method to differentiate the 2 laser beams.
: : :
: : : My partners came up with an idea that the 2 laser beams from the laser pointers are of different brightness, but I think it doesn't work.
: : : Also, we also thought of connecting a 8051 to the switch of laser pointers, and with a infra-red device which sends back the information to the 8051 (which detects gunshots from LDR) but by using this method, we still don't know which gun shoots the LDR when both guns are switch on together.
: : :
: : : any idea to differentiate the 2 laser beams? Should we use other methods to replace laser, like infra-red? because there are several LDR to detect laser, infra -red seems not a good choice because it diffracts too much.
: : :
: : : sorry for my poor English!
: : : Thanks everyone!
: : : Samuel
: : :
: Hi Samuel,
:
: As you stated before, if you use IR led's you will have problem focusing IR beam because diffraction. You can try switching laser signal (OOK, On Off) at a different frequency for each player. It works in the exact way that IR led's transmitter-receiver does. The only difference except wavelength (Laser: 640 nm, IR: 420 nm approx), is that laser beam is highly coherent, so it doesn't have high attenuation factor by distance.
:
: For each player, you can use a different frequency, through TTL IC's like 74HC14, 74LS04, etc with a couple of components. The ocillator output feeds laser (you can use a transistor for higher power). At the receiver, it's a little bit complex, using two frequency demodulator, each one tuned to freq of one player, and by direct comparition of both outputs, you can determine who shooted.
:
: There is another solution, you can try using two laser of different color (ej: red and green), and a couple receivers (LDR) placed together in the target with color filters.
:
: Good luck

I was looking at doing something of the sort (actually a cheap laser tag sort of thing). I was wondering what the difference is between LDR and PhotoDiodes.
I have a LDR and it seems like it takes a while for the resistance to change which wouldn't work because I need it to register quite quickly. Are PhotoDiodes quicker?

Any help would be greatly appreciated. Also, because the room may have some light, would it be more efficient to use IR instead of Lasers?