Data transmition using lasers?

[chrisshortys]

Hi there, I'm looking at using lasers to transmit some data. Would it be possible to use a laser to transmit a serial code to a IR reciever?

Cheers Chris

[Acetronics2]

Hi, Chris

one of our french Magazines, called Radio-Plans, had published such a project ...

yeah ... more than 25 Years ago ...

Magazine has disappeared at least 20 years ago ...

So ... U can do it !!!

Alain

[chrisshortys]

Awesome i was hoping it would be the case as the two run on very similar wavelengths!

Any suggestions on this one? I dont need to transmit much code probaly just the standard 2,# or somthing.

I had a look on the forum earlier but couldnt find any examples of IR circuits, is it possible to take the Tx and RX straight from the chip to zero volts or does it require extra components?

Cheers Chris

[Charles Linquis]

http://www.scribd.com/doc/6539201/Wireless-Data-Transmission-Through-a-Laser-Channel-Using-PHOENIX-InterfaceFinal-Model

[ardhuru]

But why specifically laser, Chris?

Whats the range you're looking at?

IR LEDs can give you a pretty good range, especially if you use optics and are careful with the alignment (which you'd have to be with anyway, with lasers)

You could ramp up the IR by using multiple LEDs.

Regards,

Anand

[b1arrk5]

We sent Morse code using a laser pointer a few years ago. Shoot the laser beam through a running 'muffin' fan. This chops the beam into a frequency that will be in the audio range. The beam then travels through the air, and hits a Radio Shack solar cell. The output of the solar cell was run into a small audio amplifier. You can then hear the audio tone, the frequency of which is determined by the speed of rotation of the fan. Using a simple shutter to open and close, blocking the beam, allowed sending Morse code to the user. The laser pointer was set up on a tripod and a spotting scope was used to align the beam onto the target solar cell. We achieved a half mile range, and were going to try going from one mountain top to another, but my helper got a job out of town, so we never went any further with it.
A Google search of laser chopper beam will show you lots of other ideas.

Jerry

[chrisshortys]

Well the idea of the project is for a local paintball site. They are planning a MILSIM event in august and they wanted somthing to simulate a laser designator for their "airstrikes". So the idea was to use the laser as they can see where theyre pointing the thing and have a reciever at the other end which the laser must hit directly.
I decided against IR Tx as you dont get a idea of where your pointing the thing and its more of a general pasting of an area than a laser which will give you a smaller target.

Ive started playing with IR Tx and Rx to get started but im having troubles with the reciever, the transmit works and ive viewed this on an ossciloscope but i dont get alot out of the Rx. In the example above there is no amplification, is this needed before the chip?


But why specifically laser, Chris?

Whats the range you're looking at?

IR LEDs can give you a pretty good range, especially if you use optics and are careful with the alignment (which you'd have to be with anyway, with lasers)

You could ramp up the IR by using multiple LEDs.

Regards,

Anand

[Charles Linquis]

Any kind of data speed will require a phototransistor (or photodiode) and some kind of amplifier.

Check out Figure 7 of
http://www.physics.csbsju.edu/~awhitten/reference/Sharp_photodevices.pdf

This circuit would have to be followed with an op-amp or (preferably) a comparator to convert the analog output to digital.

Also -
http://www.aptechnologies.co.uk/PDF/Photodiode%20Typical%20Circuits.pdf

[Jumper]

Hi,

Most cheap laser pointers are too slow to modulate but by using the idea of a mechanical beam chopper will take care of that.

Then you need an OP-amp or 2. Make sure they are AC coupled and have a decent amplifiation. After this you put a LM567 which is a tonedecoder that will give a logical signal if the tone is present.

They ar cheap, easy to use and detect small signals. If you can modulate teh laser and have a HWPM you can connect the - side of the laser to the HPWM pin and the + side of the laser to the USART tx pin or the opposite if you like to use inverted mode.

Then from the tone detector's logical pin straight in on your usart RX in the other end.

Or as mentioned before... use an already made audio amplifier and put the tone detector after it. That will work if you have a low enough baudrate becuse you need some carrier FQ cycles per bit to give the LM567 enough to work with.

/me

[b1arrk5]

If all you want to do is 'paint' the target with the laser designator, and know whether or not the laser is on target, the solar cell will work. I can't recall exactly what voltage I got out of it when we hit it with a laser pointer, but I'm certain that it would be enough to either a) bring a PIC digital input high, or b) supply enough to the base of a 2n2222 or similar transistor to make the input high. The size of the cell is around a half to three quarters of an inch by about an inch or inch and a quarter. If you placed it so that it was shaded by a short piece of tubing or something that would also give the person operating the laser something to aim at.
In this case, the only data would be on target, or not on target, so you wouldn't need to chop or modulate the laser beam, just turn it on to paint the target, and off when your done.

Jerry

[chrisshortys]

Ive been having a long think about this. I ripped an old laser quest set apart that i had from when i was younger and did a bit of research into how they worked and IR does seem to give a deffinet bonus! it would give me a very big advantage witha few dissadvantages.... i reckon i could get 150 feet range with it possibly...? then you still ge tthe issue of not knowing exactly where your pointing the thing and i still have to build all transmitters

Then reading the last post over again i got thinking and do i really need the data transfer?

Lasers are quite available esspecially in MIL SIM situations, I could just use the LDR and use some form of comparision if i can get a large enough increase from the pointer... The only issue then is the circuit could be activated by anyone... opens up a few more questions

[mackrackit]

I would think the target would need "painted" for a certain amount of time to count? Then you want to identify who hit it?

Have each laser pulse at a different rate. 75hz, 100hz 125hz... Doable with cheap lasers.
Then have the target PIC COUNT the incoming pulses for a second. If the COUNT variable = 100 then whatever.

I use a similar method for a "laser fence". If the target does not see Xhz then the alarms sound. A photo-transistor sits in the bottom of a reflective funnel about 2 inches in diameter at the opening for the target.

[chrisshortys]

ok that sounds like a pritty good idea and somthing i hadnt even considered!

So just a simple 555 timer switching a transistor to the laser with the pic at the reciever with a rang of if signal is 190-210 then target is hit by laser 01 etc?

any chance of seeing a rough circuit diagram of the way that you did it?

cheers! chris

[mackrackit]

I am using a PIC running at 3 volts and a logic level Mosfet (NPN) to the laser. A 555 would also work but for me it is easier to program the pulse I want. Sorry, I can not find a drawing.

This thead has the drawing for the target.
http://www.picbasic.co.uk/forum/showthread.php?t=6826

[chrisshortys]

Thanks again!
I shall try my best to have a play with this over the next few weeks.... Ive got my college project to work on first though!