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I have to create a local network (without internet connection) with several Pis (around 20) in a straight queue. Each Pi has to connect as many Pis as possible, but the regular case is that every Pi would have one Pi at the left side and another at the right. The Pis connection between them has to be via WiFi. The WiFi has to be visible as only one WiFi among all the Pis. Every Pi has a camera and has to send an alert (when an event happend) to every Android device connected to the same WiFi as Pis are. The Android devices have an special app designed for this.

For example: If Pi number 1 creates an alert, the message has to reach to every device connected in the whole WiFi, including mobile devices connected to the Pi number 20.

My questions are:

1) Is this possible to do?

2) How can I do that?

3) Every Pi has to be a router and then connect all of Pis between them?

4) Do the Pis need two WiFis? (One for the connection between them and the other to connect de devices)

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    A hint is "mesh network Raspberry Pi".
    – MatsK
    Commented Feb 23, 2018 at 15:43

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One possible method: choose the most central PI and set this up as a WiFi AP as well as it's normal role. Share a directory via NFS. All other PIs and Androids mount the shared NFS - any alerts are notified by a new file being created in the NFS by the PI 'sounding' the alert - either the filename or content or both can be used to carry information about the alert. A script or daemon process on each Pi checks the NFS for new alert files.

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  • Just like to comment that although this seems an interesting problem to solve, it's possibly not on-topic for this stack, and might be better being asked on Software engineering or stack overflow. I came to this conclusion by substituting 'Computer' for 'RPi' and found that it still makes a sensible question equally applicable. I.e. there is nothing in the question that makes it RPi specific.
    – Charemer
    Commented Feb 23, 2018 at 15:59
  • Thanks for your answer @Charemer. Your solution sounds very good, but i cannot set up one as an WiFi AP because the network has to be extended up to 500 metres so I need that every RPi could be an AP too. The idea about sharing a NFS directory is a solution i'm gonna study. Thanks again. Otherwise, in relation to my question on-topic for this stack, i decided to ask here because of the potential that RPis have. I didn't know if a RPi network itself could be powerful enough to keep this project alive.
    – DavidRamos
    Commented Feb 26, 2018 at 9:13
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    @DavidRamos you might want to look into ad-hoc wifi network configuration in that case.
    – Charemer
    Commented Mar 9, 2018 at 13:36

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