Connecting up to 20 slaves to one master

[Bluetoothy]

I am working with a university project where need to connect up to 20 wireless sensors together with 1 master, which will be communicating with either a computer or smartphone. So obviously the master has to be a BLE/WIFI device. But since i want to create a flexible system it could be interesting to make the sensor devices universal, so any unit could become a master or a slave.

I have been looking at nRF51822, but i am not sure if its capable of both being in standard 2.4GHz RF and BLE mode at the same time?

My idea is to connect all 15-30 sensors to the master by traditional RF, and make the master send this data to my PC/smart-device.

All suggestions are welcome, thanks in advance.

[Asbjørn]

I would recommend you to use either proprietary or ANT for collecting information from the other nodes. Since you have the nRF51822 proprietary would be the way to go for now. If you want to use ANT you have to use the nRF51422. It's the same chip, but it's possible to program ANT based softdevices into it. ANT has built in functionality for supporting lots of nodes and would probably be easier to get going compared to proprietary. For proprietary you have more options and more data through, but you have to handle a more if the behavior from your application.

There's a softdevice that handles both BLE and ANT concurrently, it's called S310. For proprietary you can you the S110 softdevice with the timeslot API. This allows you to get access to the radio peripheral for periods of time to do proprietary concurrently. There's an example here. Alternatively is to switch the S110 on and off. This takes a few millisecond and if you don't do BLE communication constantly this might be an option too.

[Bluetoothy]

Hi Asbjørn, very interesting approach. I have of course not acquired any nRF51822 units yet and i intend to make multiple prototypes of this system, so i really want to get the setup right the first time. My application is rather simple, i will be having a bunch of IMU's (9DoF) which will be sending data to the master unit for 3D visualization on a smart-device or PC, so i expect data to be close to realtime. As i understand ANT seems to be the right way to deal with this application?

[Asbjørn]

Real time requirements might not go down too well with ANT as it's built for larger networks, but with smaller amount of data and few connections each second. That doesn't mean it's not well suited for your application, but you should probably have in mind that maximum data throughput with ANT is 8 bytes per package and that you maximum can have 200 packages every second. 200 packages a second is not recommend for normal operation, but for more short bursts of stored information. The advantage is of course the built in infrastructure for multiple nodes. So if your amount of data is small and you if you think that 10-20 packages a second would be fine, then yes, you should go for ANT.

If you need to push more data through and have more packages going through, especially on the receiving side, you should consider doing a proprietary implementation.

[Bluetoothy]

I was wondering if i am overkilling this project and basically would be able to go with a simple nRF24 and traditional RF?