1-to-100 wireless communication

[cubeflake]

Hi everyone,

I'm facing an interesting challenge for a project where I'm working on. I need to communicate to about 100 devices that are spread out in a large-ish room (say 20 x 40 m). I need to send about 10 bytes to each devices at about 10 Hz. The communication will be mostly one-way, but it would be nice to get some data back every now and then (like every few minutes). My client was thinking of using (multi-router) wifi, but I think the latency would be too indeterministic. I am looking at nRF52 chips to get much lower-level control over the communication, but I'm unsure if they are suitable for a 1-to-100 set-up. I'm also looking into blasting IR from the roof, but I think it'll be hard to reach the necessary data throughput. I will probably need about 150 kbps, which looks doable with IR, but not at a distance larger than about 1 meter. Since the roof will be a few meters high, it looks like IR won't do the job.

Any thoughts?

Cheers!

cubeflake

[Skashkash]

The NRF devices would certainly do it.
  They have a fairly flexible addressing mode if you use the radio in "bare bones" mode where it emulates the older NRF24l01+ ESB protocol.
   Check the data sheet for the concept of "pipes". You could have broadcast as well as unicast addressing.

   In broadcast mode you won't have an ack response, so you may drop packets occasionally. If that's an issue, you will need to deal with that on another level.

   You could also just use the nrf24l01 radio chip added to your processor of choice.
 
     





 

[Alex Eisenhut]

Zigbee? People don't like it seems to me.

[Benta]

Zigbee? People don't like it seems to me.

ZigBee was also the first thing that came to mind with me.
It's not that people don't like it, but that no 800-lbs gorillas stand behind it (compared to, eg, Bluetooth). ZigBee is more in the realm of small- and medium-sized companies.
But it's well supported, and there are lots of devices on the market, mostly in industrial and home automation. It's just not as visible as the PC/Phone type products.

[Alex Eisenhut]

Well there's 800 lbs of particle board behind it: IKEA.

[cubeflake]

I'm definitely open to trying Zigbee, it seems quite interesting. However it looks like it's really meant to be used as a mesh network. I don't really want to use a mesh network because I want to keep the latency as predictable as possible. When used as a star network, the maximum number of nodes per Zigbee "router" appears to be limited to 32 or 64. I'm pretty new to all this, so I might be wrong about that.

One thing that I should maybe clarify is that I need to send unique data to each of the clients. So 10 times per second, every one of the 100 clients should get a unique data packet. Do you still think this is possible with the nRF chips or with Zigbee?

edit:
Alternatively, I could send a broadcast package 10 times per second, containing the data for all the nodes. Dropping a packet every now and then should be ok.

[Benta]

There's absolutely no problem using Zigbee in a star network. ~250 nodes is unproblematic.

[cubeflake]

There's absolutely no problem using Zigbee in a star network. ~250 nodes is unproblematic.

That sounds promising! Do you have any thoughts about the data throughput? If I have 100 nodes, can I update each of them 10 times per second (i.e. send 10 bytes)? At some point I'll just have to get a bunch of nodes and start pumping data, but I would like to get as much information beforehand as possible.

[Benta]

Well, Zigbee data rate is 250 kbits/s, calculate from there.

[coromonadalix]

Zigbee in a mesh network,  done that in a past for minimum 250 devices on the same network,  never had problems

[Benta]

Zigbee in a mesh network,  done that in a past for minimum 250 devices on the same network,  never had problems

Zigbee is ALSO a mesh network, but can be point-to-point or star if you wish. It's flexible.

[Benta]

Yep, just using the radio part of 802.15.4 is of course an option. That at the end can be very expensive.
FCC, CE etc. certifications are much simpler when using certified radios, firmware and protocol stacks.

Just a hint from my side.

[coromonadalix]

Esp 32 modules we hear a lot   never worked with them

[james_s]

ZigBee was also the first thing that came to mind with me.
It's not that people don't like it, but that no 800-lbs gorillas stand behind it (compared to, eg, Bluetooth). ZigBee is more in the realm of small- and medium-sized companies.
But it's well supported, and there are lots of devices on the market, mostly in industrial and home automation. It's just not as visible as the PC/Phone type products.

Philips doesn't count as a 800lb gorilla? Their popular Hue smart lighting system uses Zigbee. I have a bunch of the bulbs that I control with a Conbee II stick set up with Home Assistant. Cree, Ecosmart and Ikea smart bulbs are also Zigbee.

[cubeflake]

Well, Zigbee data rate is 250 kbits/s, calculate from there.

In terms of total throughput, it's not an issue. What I'm worried about is the latency. I need to be able to send a packet every 1 ms.

[cubeflake]

I've contacted Nordic, as well as someone I know who works at a large electronics distributor here. Nordic says it can be done using ESB on the nRF52's. The RF guy from the distributor says it can also be done using ESP32's using BLE Broadcast. So it seems this can be done, now I'm just waiting for the client to grant me the contract .