Use case, collect data from multiple sensors in a room

[Bonadio]

Hello

I would like a suggestion on the best architecture to collect data from multiple sensors in a room. Let me explain my need.

I have a room where we place multiples boxes, each box has a temperature sensor that we need to monitor in a central dashboard. The boxes enters and leaves the room all the time. We keep an average of 40 boxes in the room all the time.

The way we thought about that was:
Having 1 BLE device installed in the room connected to our network "running like a gateway" this device would be a BLE CENTRAL_DEVICE scanning for peripherals.

On each box we would install another BLE device acting as a peripheral connected to the sensor temperature from the box, at every 1 minute we would wake read the sensor and wait for the central to connect for 30 seconds then go to sleep again.

Each box must have its temperature checked no longer than 3 minutes.

Would this work?

Thank you

[Dmitry]

Hi,

If you're not concerned about security, I think the best way is to use connectionless mode - put temperature data directly into an advertising packet. In this case you're not limited with 20 simultaneous connections, and there is no overhead with establishing a connection every time.

[haakonsh]

What is the maximum number of boxes that will be in the room? For how long will they be there? 

I think the most robust solution will be 3 central devices with a constant connection to 1/3 of the devices each. By using a connection interval of 15 seconds you will save a lot of power on the peripherals as they won't have to re-establish a connection every time they need to send an update, and it will be robust with re-transmissions and channel hopping. A central based on the nRF52832 or 52840 can handle 20 peripherals each, so 3 centrals can handle 60 peripherals.  

What was your plan in getting the information off the central device, or what is your plan for the next steps of the data gathering, where does the data end up?

[haakonsh]

That'll work, but you'll have no control over this requirement:

Each box must have its temperature checked no longer than 3 minutes.

[Bonadio]

Thanks Dmitry, yes security is not a problem

[Bonadio]

Hi Haakonsh

Thanks for the suggestion.

The maximum would be around 60 boxes and they could stay from 1 hour to 24h. So the idea of 3 central with constant connection is a good option too.

To send the data to our dashboard we are thinking on the central to connect to some other mcu with wifi and send the data using MQTT feeding our dashboard, from there we can manage the alarms. 

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