Cheap bracelet with indoor location tracking

Question

I want to provide people at an indoor exhibition of ours with a bracelet which allows me to send a signal to it to flash a led light. At the same time I want to be able to determine the location (within 2-3 meters) of that bracelet (everyone wearing the bracelet is assumed to have given permission for this). The exhibition consist of 1 room (mutliple rooms MAY be needed in the future, not sure if that changes anything in technology requirements). I was thinking of some sort of radio receiver, but what kind of equipment & technology would be required to do such a thing? Also for determining the location of the bracelet, e.g. could triangulation work? (I need the cheapest solution, so probably bracelets without GPS). The battery (if any) in the bracelet would only have to last a couple of hours.

Answer 1

You probably want to check out OpenBeacon, which implements this sort of tracking using an 'Active RFID' tag. A bonus of this is that it already includes the 2-way radio you'll need to instruct tags to blink.

Triangulation is done by positioning a large number of basestations around the venue, and having tags transmit pulses at varying amplitudes. By examining which set of nodes can be reached at each amplitude, the system can narrow down where the user is likely to be. They're a little vague on what sort of accuracy the system can claim, though, or how it deals with interference due to things like obstructing walls.

Answer 2

To begin with, the location problem:

GPS would not work in an indoor venue, because a GPS receiver works by reading signals off four or more GPS satellites orbiting the earth, to compute a precise location (and elevation).

Further, even if the venue of deployment were open to the sky, non-military autonomous GPS accuracy is ~ 4 to 10 meters, while more sophisticated Wide Area Augmented GPS / Wide Area Differential GPS enhance this to perhaps 1-2 meters. However, implementing such a system in a button-cell operated, bracelet sized GPS would be a stretch.

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There are two alternatives that may be viable, neither being foolproof.

1. RF triangulation using a minimal RF transceiver in each bracelet, and RF transceivers driving antennas distributed around the room, on the ceiling perhaps.
2. Inertial location, such as is being researched for mobile phones to support indoor location systems, something like an extension of Google Maps that would work within buildings. This would require a multiple degree-of-freedom location / orientation sensor / IMU. Size, cost and battery life would be severe challenges with this approach.

Multiple manufacturers such as SemTech, Texas Instruments, Fujitsu and Analog Devices produce single-chip RF transceivers for various frequency bands. The bracelet itself can be used as an antenna, via a suitably long wire embedded into it.

Flashing an LED on receipt of a message could either be achieved by incorporating a microcontroller, or more trivially by using the status pins of the transceiver IC and some creative signaling from the base station.