I am planning to put 100+ Ruuvitag beacons(Bluetooth LE tranmistters) in a ~120m2 area. There will be approximately 1 meter distance between devices. I need to get their advertisements at once using Raspberry Pi Zero(each beacon will send data every X minutes, e.g. every 2 minutes) .

Something like this: enter image description here

  1. Any idea how many Bluetooth LE devices can transmit advertisements at once without interefering with each other?

  2. How many advertisements do you think a single receiver could receive at once without problems?

  • What are you trying to achieve with this setup? But with 120 beacons (1 per meter) and a broadcast interval of 2mins, that's an average of one per second which should leave plenty of gaps between each broadcast – hardillb Apr 17 '18 at 20:27
  • I want to get data from the beacons(temperature for example). This data is sent through advertisements(not really sure what this means though). Interval of 2 mins means that each beacon will send advertisements every 2 min, so basically 120 beacons will be broadcasting at the same time. – CuriousGuy Apr 17 '18 at 20:31
  • Only if you put a battery in them all at EXACTLY the same time, what is much more likely is that you will get an even distribution across the 2 min window. – hardillb Apr 17 '18 at 20:33
  • So, you are saying that practically their timers will have differences when measuring the interval for sending? – CuriousGuy Apr 17 '18 at 20:47
  • 3
    I'm saying that they are very unlikely to have real time clocks, they will not advertise at 00:00, 00:02, 00:04 they will just count 1000th's of seconds since they were turned on. – hardillb Apr 17 '18 at 20:56

If you add som randomness to the transmissions you'll be fine. Like 2min +/- random number between 1-10 seconds. You might not even need to do that.

As some else have already mentioned the low frequency clocks used for time keeping are not that accurate and will have a random tolerance from the factory of typ +/- 50ppm, pluss temperature drift typ +/- 3ppm per Celcius, pluss age related drift typ +/- 3ppm per year. This means that even though all the beacons are "exactly" the same they will drift out of synch as the time passes.

You should stick to one advertising channel to reduce current consumption and not drown the other two advertising channels. Alternatively you can go proprietary and use a data channel instead of an advertising channel, but that is probably not needed.

Your real challenge is WI-FI noise. If you have the ability to turn off the wi-fi modem on the raz that will help a ton.

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