Laser Transceiver (laser data link)

How to connect two computers (networks or any other electronic devices) with a laser data link.

Most used to connect lan networks between buildings this is a cheap and secure way to send information without broadcasting as RF or wifi links.

This project was developed in my course of robotics for high school junior level, is very cheap and easy to build.

What we get?... communicate two computers over 1100 feets (345meters).

See step 1 below.

Step 1: What we need?

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The laser transceiver consists of two identical devices.

Hardware.

Both endpoints have the following electronic items:

- Microcontroller ATmega168 to 20MIPS.
- Visible light laser 650nm 5mW of power.
- Trigger for the laser based on a MOSFET IRF9630
- Receiver based in three photodiodes of visible light SFH203.
- 50mm Reflector to open the receiving surface.
- USB to Serial Converter at TTL levels.
- Power via USB or battery of 4.5-5V.

Optionally if you need a long distance you must build an accurate pointer system as this based in screws.

Cost.

- Atmega168 + self-made board = 10 euros
- USB-Serial converter = 4 euros
- Mosfet = 1 euro
- Laser = 3 euros
- Photodiodes = 1 euro
- Torch (only use the reflector) = 2 euros
- hardware & cables = 5 euros.

About 25 euros each transceiver.

Correction the Wiznet W5100 ethernet http://www.wiznet.co.kr/product-item/w5100/

Ever thought of taking SPI out of the Atmega 168 directly to a MAC enabled ethernet chip?http://www.microchip.com/wwwproducts/en/en022889

Interesting project. I've stumbled on this one trying to find out some details for my own project. I'm thinking of hacking a couple of media converters. Get two second hand Ethernet to fibre optic media converters and put a laser / photo diode set up on the front end of each converter. Did you try any thing like that ? I think if it works it will make things a lot easier as you'll get 10/100 mb speed and wont need any other hardware as both computers will think they are on normal Ethernet network. I actually want mine to work under water but that's a different story...

Did you ever try the media converter hack?

Yes, it works well providing you get fast enough leds. Problem it the faster you modulate the shorter the distance. We had some success with laser diodes as well but overall it didnt work for my project so got scrapped. But it is worth developing, if you try it let me know how you got on...oh and be careful with the media converters and their lasers..im not sure but i guess they could damage your eyes si dont chance it.

Hey Perfo,I have limited data internet over the phone and it is expensive compared to line internet. Obviously. Can't use RF based solutions as there is a huge possibility of interference due to unavailability of fully clear line of sight. But I do have a line of sight.Can you please share a little more details about your hack. Can you give out details of the media converter, LEDs, receiver and other hardware that you used for the project and what were the problems that you faced? I would really appreciate if you give out these details.Thanks in advance

I doubt this is fast enough for quality data transfer and that laser and photodiode is probably not fast enough to operate in the MHz stably. I would recommend an avalanche photodiode and an IR laser diode (850nm or 1310 nm).

i need example code for send & receive maybe arduino ?

You just can Connect the Laser to Pin 0 (TX) to the laser and connect the photodiode to 1 (RX). Do so with 2 Arduinos. Now set a Low Baud (1200) and Print Something in the Serial Monitor on the First Arduino and it will Echo at the Second!

Cool Project!

Hello everybody,I am really interested in that project, but I notice some lake of information.For example the value of the two capacitors, the value of the resistance behind the Mosfet.I also think there is a mistake in the simplified schema.I am trying to improve the PCB design and will post an Eagle link of it.Please, I need those informations to complete the schema.Can anybody give me a hint ??

The resistor behind the mosfet is 10k, but i cant make out what the one next to the LED is... probably like 100 ohm? Theres only one capacitor, 100nF (yellow) The orange one is a 20MHz resonator :)

Interesting project, I've been trying to rebuild much of the stuff here. However, I've so far encountered a few problems.First, I don't think your MOSFET connection is correct. The Vcc input should be placed in series with the laser diode and the Drain pin of the MOSFET. I tried it this way instead and it worked.Second, I tried to connect the photo-diode using the same circuit as yours although I tested it in two load resistor sizes - 100 K and 3 M. I noticed (Using a othoscillope) that the photo-diode circuit exhibits a RC effect where on the switch off stage, the voltage gradually drops off rather than instantly. This problem is really serious because that drop off thing is a constant value in time. So if I notice this RC effect on say 1kHz, I'm going to have huge problems at 10kHz since that RC constant will become very large (Look at attached images).This problem gets worse when I increase the resistance (Once again, refer to the attached images, pay extra attention to the frequency written on the bottom of the graph). So how did you resolve this RC issue in your project?

Hello :) Did you ever finish the project? In that case, can you tell me how you solved this gradual drop?

OK, so why we don't build a high communication tower at the middle of each neighborhood with transceivers to and from houses (pro grade transceivers) to get real nice internet to those houses instead of the crappy DSL we have right now ?

What is the name of the model of USB to Serial Converter at TTL levels are you using ?Thanks for you time and nice project

Hi, can you post the source code for this?

Hello Sir, It is a really nice project. Can you please tell me how do you foccus the light on the laser? Did you use a lens? Can you show us more images of the mounting of the laser and photodiode? Did you test the same system for 345 m?

Hi, very nice work! I will give it a try... do you remember at which baudrate you tested your transceivers? Have a nice day, Alex

Hi, thank you very much for sharing this with us. I wanted to set this up to use over 2km distance. Any ideas how to aim lasers at exact point at such a distance ? Thanks.

i want to connect pic to pc through rf and use pic as web server. can any one help me?

Hello, I wanted to communicate two Computers Via Laser beam (same as above using unguided media, no optical cable, wireless communication): Please do share with me. Also If you able to create that type of hardware, tell me the cost and time u complete. Hope you understand what I needed, Thanks for your time and consideration, waiting for your response. Thank you Muhammad Arsalan Bukhari mr.bukhari88@yahoo.com Call: +92-346-3242448

Hello, about SFH203P, how do I connect it directly in arduino? I'll need to use the MOSFET and RESISTOR of 1Mohm to PHOTODIODE? I made the connection with the photodiode using the 1Mohm resistor and it did not work. Can you help me? I have a seeduino with ATmega 168. Thank you.

Hello i have Arduino uno r3 ,how to connect laser and photo diode to Arduino uno r3 kit can any one help me pls i m new such proj . my proj title is pc-pc laser comm. pls help me out. can any one send me details .......to rajchav@gmail.com

Maybe you must read step 2 of this project... :P good luck

k thanks . but i am facing prob in writing code. can i use same code what u shown in step 3.

Great project Instead of SFH203 can you use a solar cell?

¿solar cell or LDR (light dependant resistor)?... anyway, we didn't use LDR because is very slow. Solar cell is not a sensor, you can use it as a light sensor but in long distances the laser power is very weak, maybe not enough to activate de solar cell... check it and share with us the experience... ;)

can send data?..

Is the tittle... "data link" You can use any terminal software (as Hyperterminal of windows) with serial protocol or make your own program using com ports, you can see a video in step 4.

Could you explain what MOSFET IRF9630 is used for?

The standar pin of a microcontroller provide up to 20mA to light a standard led, but motors, bulbs or lasers uses more than 20mA, with this mosfet you use 20mA to operate up to 9000mA devices...

I see, Thank you :))

For people interested in this, you may want to check out Ronja also, http://ronja.twibright.com/ It is pretty awesome, with massive possibility :)

I hear about Ronja project thanks our main sources of the preliminary information... the "Laser Game" of my friend Heli. http://heli.xbot.es/wp/?p=27

That is quite a nice setup =D It would be nice to see a variant of Ronja that had quicker transfer rate, they where developing them but I'm not sure if anything has happened with it lately or not. I think I will have a go at constructing a Ronja unit soon, though 100mb - 1gbit speeds would be nice to rival current wifi connections.

how much have you spent so far?

Not much... - Atmega168 + self-made board = 10 euros - USB-Serial converter = 4 euros - Laser = 3 euros - Photodiodes = 1 euro - Torch (only use the reflector) = 2 euros - hardware & cables = 5 euros. About 25 euros each transceiver.

excellent ! Thank you for the idea and good luck with your school and projects, keep at it and hopefully i can do something with it too!!

add one more euro for the mosfet... Thanks for the questions, i'm adding this information to the project.

What speed can I expect from this

Our system with cheap lasers, mosfet and photodiodes work at old modems speed. We use Atmega168 at 20MIPS so working with high quality lasers you can get near 10Mbits/s, using faster microcontrollers, lasers and receptors... no limit. Seeking internet you can get information about military investigations, NASA and ESA too are working with Gigabits. The final speed depends on your resources.

Why not connect the dots with fibre optic?

Because we want to investigate about wireless system not based in RF.