proximity-sensor
I'm looking for a way to track people in rooms.
iBeacon track Smartphones. But it requires people to have a smartphone.
I'm looking for a reverse beacon ? People wear iBeacon and trigger a kind of BLE "light smartphone"
(There is RFID answer put "it's complicated" and imply antena, etc … )
Any Ideas ?
Mouser's latest mailing mentioned this one: Vishay VCNL4000. For the price of the proximity sensor you also get an ambient light sensor. 4mm x 4mm, 0.75mm high, though it has three blobs on it which make it somewhat higher. Still looks like it's less than 3mm.
Detection range for the proximity sensor is only 20cm, though.
disclaimer: the mention of Mouser is not a shopping advice :-)
Pretty sure they use radar for adaptive cruise control in cars. Check this sensor out:
I've heard them called "headway sensors" or "radar headway sensors". There are other technologies like acoustic but I'm not sure if they'll have the range you're looking for. Laser could work but it's aim is pretty narrow, dust dirt and fog can get in the way etc.
Good Luck!
Best Answer
Yes, it would work just fine in theory.
However, it will stop working well when you have too many people (beacons) all in the same area. Each beacon is an uncoordinated transmitter and its messages can and will collide with others. Messages will also be garbled by interference from other 2.4GHz transmitters (WiFi, other Bluetooth devices, microwave ovens, etc).
Also, at some point you may have a large number of beacons (e.g., 100) and in each interval (e.g., 1s) the receiver will only see some fraction of those (e.g., 50%). While that may seem okay and you might think that you should see them all in a few seconds, it can take a while to see the last few. It becomes a variant of the Coupon Collector's Problem.
The question of where it breaks down is left as an exercise for the reader. Others on SO have reported at least 20 beacons working nearby with no problems, but your mileage may vary.
In regards to using an embedded Linux computer (Raspberry Pi) to scan for beacons, there's this question on SO and this guy's Github project.