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I would like to know if it is possible to connect an RF(radio frequency) module to my smartphone and find the distance between them with an accuracy of about +/-2 meters. To find distance I believe I have to use RSSI level (Received signal strength indication). I have considered using bluetooth but I would like to find better alternatives because I need more range than bluetooth can provide. I need to measure distances up to 100m/300 feet. I found some module from ebay that transmits 433MHz. Is it possible? Thank you.

Example module: http://www.ebay.com/itm/433MHz-100-Meters-ASK-Module-Kit-RF-STX882-Transmitter-SRX882-Receiver-Antenna-/401186085838?hash=item5d688ddbce:g:ejIAAOSwAuZX1AMm

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    \$\begingroup\$ This has been asked many times before. Basically this is impossible as signal level is influenced by many factors like antenna patterns (the devices are not equally sensitive in all directions), surroundings (signal is reflected or absorbed) interference from other devices. If you can make a working prototype of what you want and get that to work in a realistic environment (not a faraday cage) then you'd be the first. \$\endgroup\$ – Bimpelrekkie Oct 10 '17 at 8:21
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    \$\begingroup\$ @Bimpelrekkie I think I can pull it off if you give me a few ceasium beam clocks... Oh wait, that's called GPS. \$\endgroup\$ – Joren Vaes Oct 10 '17 at 8:27
  • \$\begingroup\$ But is it possible to connect 433Mhz module with a phone? Can the phone detect 433Mhz frequency? \$\endgroup\$ – Mark Oct 10 '17 at 8:31
  • \$\begingroup\$ Phones cannot detect 433MHz. You could stick two modules to phones and have them communicate somehow, but that doesn't solve the fact that RSSI gives you a very inaccurate measurement unless both phones are in a field. \$\endgroup\$ – pjc50 Oct 10 '17 at 8:43
  • \$\begingroup\$ It might not be extremely accurate, but it has been done with bluetooth devices(iTag, iBeacon) so i imagine it can also be done on another frequency. \$\endgroup\$ – Mark Oct 10 '17 at 9:43
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To do this with RSSI is, to put it mildly, very hard. There is so much influence of surroundings, reflections, etc. that makes it virtually impossible to do this in any situation where you are no in an anechoic chamber. Not to mention the impact of antenna directivity, how you are holding the device, etc.

I think it would be easier to use something like GPS to determine position and transmit that, and calculate the distance by just looking at the distance between the two gps locations.

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  • \$\begingroup\$ yes, differnetial GPS can give a high precision. but you need a way to transmit it 100m - wifi with a beam antenna perhaps. \$\endgroup\$ – Jasen Oct 10 '17 at 8:41
  • \$\begingroup\$ If you've got phones you could have the reconcile GPS measurements over the data network. I'm not sure what the data rate requirement is though. \$\endgroup\$ – pjc50 Oct 10 '17 at 8:44
  • \$\begingroup\$ @Jasen I think it's easier to go for one of the lower frequency ISM bands (like the 433 MHz one). Getting that range will be much easier at those frequencies, and datarate is likely not an issue here) \$\endgroup\$ – Joren Vaes Oct 10 '17 at 9:13

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