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I am trying to develop a proximity logger.

Basically I have 2 mobile devices (microcontrollers), when the devices are within a 1-2 meter from each other, they should exchange IDs (a simple integer value or short string). The ID should then be logged (so some serial connection). When the devices loose communication, it should again be logged (just interrupt the microcontroller).

I've done some research, effectively I'm trying do NFC but for a longer range and small data transfer.

Any suggestions on hardware I could use, or alternative research I could look into?

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  • \$\begingroup\$ Using RF devices, what seems like a reasonable range of 1 to 2 metres is probably going to change to 0.1m to 10m in differing setups in different places. \$\endgroup\$ – Andy aka Mar 4 '15 at 10:18
  • \$\begingroup\$ But I will be able to control the range by increasing or decreasing the power, correct? \$\endgroup\$ – Ricium Mar 4 '15 at 13:50
  • \$\begingroup\$ I think you misunderstand what I'm saying. If you want a range of between 1m and 2m, depending on "other" things this range might become much less in some areas around the master device and simultaneously much greater in other areas. "other" things are proximity to interferers and large pieces of matel for instance. \$\endgroup\$ – Andy aka Mar 4 '15 at 14:24
  • \$\begingroup\$ Oh okay, I see. The application I'm looking at is for cattle. So it will be deployed in areas with hopefully minimal RF interference, most likely open fields with minimal trees, and large flat surfaces. \$\endgroup\$ – Ricium Mar 4 '15 at 14:28
  • \$\begingroup\$ Have you considered ultrasound technique? You can easily measure distance and you can also transmit and receive a few bytes of data using cheap hardware. \$\endgroup\$ – Nils Pipenbrinck Mar 4 '15 at 17:02
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ISO15693 13.56Mhz RFID tags cover a range up to 1.5 meters if you have a big antenna. That would be a cheap solution.

One more option would be to use some cheap 433Mhz transceiver chip and run it at low power to limit the range.

Also Bluetooth Low Engery may be used. Some transceiver allow you to measure the field-strength. This can be used to approximate the distance between the two devices.

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  • \$\begingroup\$ I assume multiple connections would not be possible? The "tag" should serve both as a reader (in the sense of a conventional RFID reader) and a tag. Is such a thing possible? \$\endgroup\$ – Ricium Mar 4 '15 at 13:48
  • \$\begingroup\$ Bluetooth LE seems like the obvious choice indeed. It's widely used in consumer electronics for exactly this purpose. \$\endgroup\$ – Mast Mar 12 '15 at 9:09
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I have decided to use XBee modules, and by means of signal strength determine proximity. It is by far not the cheapest solution, but it will allow long distances, and communication to a 3rd party device to process some data.

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