Infrared LED communication question

Discussion in 'The Projects Forum' started by KOOPI, May 15, 2014.

  1. KOOPI

    Thread Starter New Member

    May 11, 2014
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    I built an IR communication system . the transmitter controlled by arduino and modulated in 38Khz. the reciever is also controlled by arduino (another one) and demodulting the transmitter signals. everything is great so far. now i want to enlarge the communication range up to 1 kilometer and even farther. how can i reach this range (not involving any optics - telescope and ect.) by replacing to a very powerful led?
    or optics is necessary for this kind of ranges?
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I'm pretty sure you can't get there.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Two words: LED laser.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    Depending on where you live you can get a laser pointer from the dollar store for very low cost.
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
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    With a laser emitter you might not need optics for the comm path, but you will need a scope for alignment. Lasers have great beam density and almost no divergence, but that makes hitting the receiver even harder.

    Also, at these power levels you risk serious eye damage to anyone or thing that interrupts the beam. This is extra-true for infra-red emitters.

    ak
     
  6. ErnieHorning

    Member

    Apr 17, 2014
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    You also risk liability issues if somebody gets hurt. Realize that a laser can change direction when it’s reflected. I know some people with permanent marks on their retinas due to a laser light show device. It only takes one quick pass to make a stripe. :eek:
     
  7. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    true for only expensive\quality lasers. the $1 pointer items at the checkout counter will not make 1km.
    5Ghz Rf w/ yagi seems like a better option for km comms length. if this is in the US then i am not sure if the FCC max power density in this unlicensed band will reach 1km.

    search gool for "FCC Regulations for Low-power Non-licensed Transmitters", should be 1st link with PDF.
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    1km is really not that far. My old house was across a small valley from houses at 1km, and I could see all their lights and details. Even a cheap 1mW laser shining in my direction would have been very visible to the eye at 1km.

    All you need are some bright IR leds, and a sensitive enough receiver. A standard 3pin IR receiver is not good enough I would use a high gain opamp and tuned circuit at 38kHz (or whatever freq) and a 38kHz tone detector.

    If you are using a micro for decoding you can detect the carrier freq in software which makes the receiver hardware much easier.
     
  9. #12

    Expert

    Nov 30, 2010
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    Just wanted to confirm the difficulty of aiming a laser. One day I was calibrating a laser and the spot started jumping all over the target. My equipment was bolted to the concrete slab, so I thought about a truck in the parking lot. Not being able to detect any nearby machines or vehicles moving in the industrial park, I looked farther. It was a freight train going by on the plain about 200 feet below my plateau at nearly a mile away.:eek:

    Just saying, when it works, it's good, but you'd be amazed at the kinds of things that can cause interference with a laser link.
     
  10. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    how about weather? will you get comms down and a light show from refracted laser? 1km = ~2/3mile. fairly far for a laser that doesnt cost arm&leg. i just think Rf and yagi seem easier and more reliable. but hey, i would like to see attempt and results of laser.
     
  11. Little Ghostman

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    Jan 1, 2014
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    We had a line of sight laser system on the farm, it was something to do with field leveling and the tractor's, I dont remember much about it, I know that the furthest point was just under 1km, and I know that heavy snow meant it lost connection, I dont remember any times that rain stopped the system, but I would have to ask dad.
    The newer systems they use are all GPS now, I also remember the unit with the laser in was pretty small, the collector bit was about as big as a dinner plate but had a small dot in the middle.
    As for IR I know it travels more than you think it would, and seems to be brighter than a normal led. When I have been ratting or bunny hunting on the farm with dad in the dark, we had IR lights on the air rifles, it surprised me how much they can pick up with the right receiver, the scopes were from dad real rifles, and they were probably not cheap, so I dont know how much of what I saw was because of the optics on the scope or because of the amount of light from the led.
    But I could see thing very clearly in the sights way beyond what I could shoot with a air rifle.
    But then you look at the cost of radio Transceiver chips, and cheap Chinese I2C units, and have to ask why choose IR over them?
    If itsa just because you want to use IR or laser then ok thats a cool thing to try, but if it's a serious reason or need, then I would look at other ways. I did the famous laser spy mic! was a pain to set up but did work kind of well on widows or metal sheds :D, you could normally hear pretty good, the hard part was getting the return angle right.
     
  12. enggricha

    Member

    May 17, 2014
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    1$ lasers and IR receivers? I am pretty sure that wont work over 1 km.
     
  13. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    ooober sensitive receiver with a large target, rock solid transmitter, clear sight, no weather ,,,,,,,, then maybe.

    next might be electronic vibration compensating optics so that movement in the transmitter doesnt change the direction of the laser itself. sort of a gyroscope in the electronics control form.
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    You can get high power IR LEDs with 10 dgree output beam, so aiming it should not be any trouble at all.

    What it needs is a really sensitive receiver and decent transmitted power. Not some specialised transmitter alignment. :)
     
  15. enggricha

    Member

    May 17, 2014
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    such a sensitive receiver will then need protection against broad spectrum ambient IR... cant think of a reliable way to do that.
     
  16. enggricha

    Member

    May 17, 2014
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    gyroscope !! i dont think vibration itself is a problem here, unless ur in a seismic activity zone.
     
  17. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    didnt post #9 tell the story of vibration issue from far away?? and for tidbit info, seismic goes on all the time, even small items not noticed by humans in their daily activities can pose an issue.
     
  18. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    www.edmundoptics.com, source for lasers, laser diodes, anything optical, but make sure you have a fat wallet.
    Longest detected red pointer distance that I have tried is about 300 ft with spot of 1 in, Bet spot at 1 km would be around 10 in, might call for a compound parabolic consentrator for only $ 96.
     
  19. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    that 10" spot means more $$ in the transmit power or receiver sensitivity. i suspect the SNR on the receiver end is the bear in the woods? perhaps spending a tad more $$ on a better laser would be best/easier method to get good results?
     
  20. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I presented it in post #8; use a tuned circuit on the receiver at the 38kHz or whatever the transmitted freq is. Ambient light will have little to no natural 38kHz component.

    The receiver problems have all been solved in RF designs, where they need to detect much smaller signals.

    These days with a micro on the receiver it gets even easier, you can easily do precision DFT etc on the signal to give massive noise rejection of all frequencies but the xtal-locked freq of the transmitter.

    I'd just hook up a small array of 20W of IR leds, point it roughly in the right direction, and pick it up 1km away with no problems at all.

    See this page;
    http://modulatedlight.org/optical_comms/optical_index.html
    "Left: A 3-watt red Luxeon LED at a distance of 14.91 miles (23.85 km) with downtown Salt Lake City in the foreground.
    Right: Transmitting with a 50+ watt LED with the light from the 95 mile (152km) distant end being visible at the terminus of the red beam."


    1km is nothing. The world record for LED comms is 173 miles.
     
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