Transfer Data with Lasers?

[mfo]

Isn't this more or less how fiber optics work? Except fiber optics are not airborne.

 

[gotwake424]

Isn't this more or less how fiber optics work? Except fiber optics are not airborne.

Yes for the most part, that is why we are saying that the amount of data that you can send and receive with this setup is only limited by the sensor and the program.

 

[mfo]

Yes for the most part, that is why we are saying that the amount of data that you can send and receive with this setup is only limited by the sensor and the program.

How much resistance is in Fiber Optics? Like are they efficient at transporting the data?

 

[lasersbee]

A few years ago we designed a Laser Data Link between 2 buildings.
We used cheap $1 Store red Lasers modulated at 40kHz.

On the receiving end we used a modified 40kHz IR demodulator receiver
and changed the IR sensor for a large area Silicone Pin Diode sensor..

We transmitted 9600 baud RS232 coded signals...

It worked very well until it rained...snowed... was foggy... etc...
and any small vibration on the laser end would miss the sensor
until the vibration subsided...
So it is feasible....



Jerry

 

[ElektroFreak]

I currently own a labby which modulates at a max of 30kHz. While this is not extraordinarily fast I guess it would be enough.
The 412mW burst of green should be plenty to communicate with someone several miles away.
I prefer the interwebz or mobile phones though.

Seb

DPSS is much slower than just a diode, so you're much more limited. Also, with light communication being line-of-sight, you really don't even need that much power to go just a few miles. In the article I talked about before, the guys involved were communicating across a harbor, using ~5mW.

 

[gotwake424]

DPSS is much slower than just a diode, so you're much more limited. Also, with light communication being line-of-sight, you really don't even need that much power to go just a few miles. In the article I talked about before, the guys involved were communicating across a harbor, using ~5mW.

Elecktro do you have any idea at what they were using for a sensor? Sorry i did not get a chance to read that article.

 

[ElektroFreak]

I can't remember off the top of my head, but I know that alignment was crucial. Just a few feet off target on the receiving end, no signal at all. I would imagine just a normal high-speed photodiode would do the trick, as long as it's in the center of the beam. A beam expander was used, and there might have been optics on the receiving end to focus the incoming light onto the photodiode, but I'm not 100% sure of that.

 

[mfo]

Awesome stuff guys! I wanna build some sort of communicating device now hehe

 

[millirad]

It could work however, I just pefer to use the tried and true method of the "pony express". Some may argue that you have to feed the horses, but at least you know the document sent is the document received and no encryption required. That newfangled technology is just to impress your friends. So give the "pony express" a try, I think you'll like it.

 

[Benm]

I'm sure getting coms in the kHz speed range would be no problem at all, and this has been done many times by various people.

The intesting part, i think, is the real limit on the speed you can obtain using a dyi system. I'd say at least several MB/sec should be feasible. I suppose the chief problem is building a system that works at these speeds, even if the laser and sensor where right next to eachother.

In the kHz systems the serial port was a convenient interface between electronics and computer, but at these speeds you'd clearly need something with a bit more punch. Ethernet (10BASE-T) is a likely candidate, but that would require a bidirectional setup even for testing purposes.

 

[Jaseth]

Wow guys I learned a lot of new stuff on this thread! My first thought was "this would be so slow, why wouldn't you just transfer is over the internet?" but now I see that the possibilities are actually really great, especially using a diode laser
I have to try one of these with a friend.. I can see his window from mine even though we are about 800m apart.
Thank you everyone for your input, really interesting to learn something new!

Seb

 

[Benm]

I'd start with a small setup, just the laser and the sensor in the same room... and see if you can get the electronics side of it to work at all. I would imagine the nicest solution would be something that responds the same way an ethernet cable does. These things work with pretty fast differential signals, so its not the easiest thing to rig

 

[ElektroFreak]

Unlike typical laser modulation, with data communication the signal never goes as low as 0V. All you need is a high and low voltage to communicate data, so rather than actually turn the laser on and off with each data bit, you just dim and brighten it. This allows for even higher speeds than if you were to actually pulse the laser on and off.

 

[Jaseth]

Benm: Yes of course, I am not going to try to align the laser perfectly with the sensor at his place while developing and adjusting it
I think the hardest job will be to interpret the information.. I will have to ask a friend for help there.

EF: That's good to know With my DPSS unit it is 50% faster when using TTL modulation than with analogue, so thanks for letting me know that the opposite is the case with diodes!

Seb

 

[lasersbee]

Because of the receiving end of the system... the ambient light from the outside
world has a negative effect on the receiving sensors ability to see small laser level
variations.
By modulating the laser... like a carrier wave... and demodulating it it at the
receiving end.. it will easily block out unwanted signals (varying light levels)
and more easily see the true ON/OFF data...

For example... using an IR LED and IR photodiode with no modulation... just pulsed
on and off at 100 hz I get a detection distance of 2"-6"...
But when the same IR LED is Modulated at 40kHz and the Photodiode Demodulates
the ON/OFF pulses at the same power levels I get a distance of over 30 feet.


Jerry

 

[ElektroFreak]

EF: That's good to know With my DPSS unit it is 50% faster when using TTL modulation than with analogue, so thanks for letting me know that the opposite is the case with diodes!

Seb

That's actually a limitation of the driver. The laser module itself would perform differently with a different driver.