Data transmission

[tekollt]

@furrtek have you tried the opposite way around, not updating the ESL`s but reading out the data?

Considering that the IR is not bi-directional i assume that there is a general broadcast from the TRXs and if it has the label`s id - it will take that information and update it self.

It would be interesting to see if we can read this transmit, have you tried such a thing in your lab or setup?

[furrtek]

I haven't tried it, but I can't imagine what would prevent that from working.
To receive the weak ESL ack signals, the TRXs use shaped reflectors and a rather complex circuit for very high gain amplification.
Receiving the downlink signal however should be easier given the power at which updates are transmitted.
Fast photodiode -> bandpass -> AGC -> AM demod / carrier detect -> microcontroller might be enough.

Modern installations have ESL roaming detection, allowing updates to be broadcast only by TRXs located around the last known position of an ESL. If there's no ack from it, then the update is broadcast again store-wide this time to detect where the tag has moved. This might make complete store updates logging difficult with only one spying device.