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I am looking for a cheap single wired solution to transfer data of some sensors connected to a uC over a distance of 1 KM from a control room on UART. The data is of 16 bytes, no high speed communication is required and also the data would flow only in one direction ie from sensor to control room.

What solution would you recommend and which kind of wire should I use?

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    \$\begingroup\$ An optical fiber line. \$\endgroup\$ – Adi Jun 5 '14 at 9:08
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RS485 over unshielded twisted pair, e.g. cat5, should deliver what you're looking for. Drivers, receivers and cable are cheap and readily available, and 1km is well inside the working distance for RS485.

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I think you need RS485. It has differantial 2 wire communication (i know you said single wire but probably a single wire solution wont do). It can communicate distance of 1.2 km (http://en.wikipedia.org/wiki/RS-485)

there is popular IC max485 or others that can communicate with MCU

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Do you want to use a single wire (plus ground)? If so, current-mode signalling works well. This is the same type of signalling that was used with Teletype machines before they were replaced with modern communications systems. The current used was usually 20mA and the usable distance was many miles.

Question: why are you limited to using a single wire? As has been mentioned by others, RS-485 (bi-directional) or RS-422 (single direction) signalling is robust and easy.

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I'd seriously consider radio such as this one: -

enter image description here

It's good for 5km so 1km line of sight should be OK but there will be more powerful devices that fit the bill. It came from here. Here is more detail: -

The TX3H-869.5-15 from Radiometrix, is an FM transmitter module achieving a power output of 450mW at 869.5MHz. It is fully pin-compatible with the company's established range of SIL TX modules and is a drop-in UHF replacement for the TX1H VHF product, having near identical dimensions of only 45x17x6mm.

TX3H is an excellent choice for the designer of a licence exempt wireless data application where the size of antenna is restricted yet a range in kilometres is also specified. The module can support data rates of up to 15kbits/s and has a potential range of 5km or more when paired with Radiometrix receivers such as the new RX3G, depending on the type of antenna used and the environment.

It'll save you a few pennies on cable install costs.

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This is what I have bought: http://www.ebay.com/itm/NRF24L01-PA-LNA-SMA-Antenna-Wireless-Transceiver-communication-module-2-4G-1100m-/310651702557?pt=LH_DefaultDomain_0&hash=item485448cd1d

NRF24L01 it uses with a big antenna on it. I haven't tested it yet, though they claim over 1KM distance. Board has 10 pins on it. It uses serial communication, though I can't remember whether it was UART right now. There is no pin label on header pins.

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  • \$\begingroup\$ Actually I'll be interested to hear how it goes, for some modules the range is very optimistic. Updating your answer (and please ping me back) once you've done some testing would be very useful for future visitors sometimes it's hard to find real-life results on the range of various module / antenna combinations. \$\endgroup\$ – PeterJ Feb 6 '15 at 11:59

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