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I'd like the distance to be about 1/10th of a mile; less distance will be fine if that's easier to build. What tools and parts may I need for this? I have plenty of LEDs lying around and I have breadboards. I should add I've been working with electronics on and off for about a year so I just need directions and a tools list.

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  • \$\begingroup\$ LED emitter, LED receiver, Amplifier, and a Lens to focus the infra-red beam. Also something to encode / decode the data into the light. Just like a TV remote control but with brighter IR LEDs and a more sensitive amplifier. \$\endgroup\$ – Majenko Dec 25 '14 at 18:39
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    \$\begingroup\$ Less distance is always easier, so what's your lower limit? \$\endgroup\$ – EM Fields Dec 25 '14 at 20:07
  • \$\begingroup\$ IR/visible light LEDs? \$\endgroup\$ – hryghr Dec 25 '14 at 20:26
  • \$\begingroup\$ Visible lights preferred \$\endgroup\$ – Foo Fighter Dec 25 '14 at 21:41
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There are several optical free space communication designs as part of an open source project called Ronja (Reasonable Optical Near Joint Access). They have plans, schematics and software published under the GNU Free Documentation License. They claim a 1.4km range with a stable 10Mbps full duplex data rate, the system uses either IR or visible light LEDs with focusing optics, and interestingly does not seem to use any spectral filters.

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What will make a system like this work is the ability to focus the beam from the emitter. A regular LED converts electrical power to light power and this spreads out as distance increases - precisely like radio waves from an antenna. So, if you can focus the beam, more light power will hit the receiving device and there will be a bigger signal received - important because you'll be fighting against noise and you will need as much signal as you can get. maybe try a low power focussed laser LED as the source.

What you have lying around might work at 10m but not 150m.

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  • \$\begingroup\$ for an led consider a laser diode. \$\endgroup\$ – russ_hensel Dec 27 '14 at 16:02
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A 160 meter long visible light data link is not an easy thing to achieve with off-the-shelf LEDs and photodetectors. For comparison, I recently designed a low-power visible light transmitter, and it was only able to work at a maximum distance of ~1 m (where the bit error rate was already quite high @1 Mbps) having a receiver at the other end which was created for simple measurement purposes. It was this LED with a forward current of 20 mA.

Obviously, you can use power LEDs with better directivity, lensed receivers with better responsivity/sensitivity, your environment might be less noisy, you can lower the datarate etc, but to increase the distance to 160 meters, you need components/devices that are usually not "lying around". Infrared might be somewhat less difficult, as most photodetectors tend to have better responsivity at IR wavelengths.

I recommend you to read about free-space optical communications.

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I agree with russ_hensel, a laser diode is easy to obtain and can be modulated with a transistor, transformer or another form of switching. The distance is much more then a focused led. I dont have the schematic anymore but my nephew and i made a laser voice link for his science project. Worked across his school yard with no issues other then aiming it.

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