I am wondering if anybody has ideas for developing an (Arduino?) system that would use RFID to log occurrences when two people are in close proximity to each other (e.g., <= 1 meter). Ideally, I would like to construct something that would operate in a manner very similar to the OpenBeacon system (http://www.openbeacon.org/) -- and, preferably, the events/data would be transmitted via wi-fi in real time.

My ideas are as follows, so any feedback or alternative solutions would be greatly appreciated. (Please keep in mind that I am not an engineer!)

I am thinking of using a wi-fi enable microprocessor (e.g., Arduino Yun) that would serve as the reader or detection system. For beta-testing, this device could be set in an enclosed case and attached to a belt. I presume it would require a fairly robust battery supply. The other person would be wearing an RFID tag that has a range of <= 1 meter and would log the event. Ideally, a reading would take place roughly every 30 seconds, and the captured event would be transmitted over wi-fi.

Here are a few other things to keep in mind:

The people using the hardware should not have to do anything other than simply wear the constructed devices.

The reader itself should be as small as possible.

My ultimate goal is the data logging of the proximal events.

I am certainly open to other technologies, as my ultimate goal is simply the proximity detection with data logging (preferably via wi-fi).

Thanks in advance! Brian


RFID would require quite high gain antenna to work at that distance, but it's certainly not impossible. RFID is not designed to work at that distance, as passive tag gets the power over air. There would also be problems of interference if multiple RFID-tags would receive the signal.

My first thought is to use pair of smartphones for the proximity detection. You could use one phone's WiFi to scan nearby APs and detect if the other phone comes in range. With the signal strength, you can approximate how far the other phone is.

You also could fo this with other RF-chips and Arduino Yun. For example, you could use pair of nRF24L01+ (it's cheap and there's a lot of examples available), one connected to Yun and another to another microprocessor. Configuring the second one as ping-back node, you could measure the distance by sending ping-packet from Yun and measuring the time it takes to get an answer from the other node. This solution also enables monitoring distance to multiple targets.

  • \$\begingroup\$ Time-of-flight measurement i.e. ping-back time isn't likely to be a viable method of distance determination in this situation: The difference in time for a radio signal to travel say 4 feet versus 400 feet is too small to be distinctly measured by consumer-grade devices and parts such as described. \$\endgroup\$ – Anindo Ghosh Feb 5 '15 at 5:40

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