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[Q] Most efficient/effective way to connect Bluetooth to embedded device

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By hedpe, Senior Member on 14th June 2014, 05:45 PM
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I have: 1) An embedded device with a Bluetooth connector that I use with BlueZ, and 2) I have an Android phone that I am writing an application on.

Goal: I want to make sure that when these two devices are near each other, they quickly detect each other and establish communication. Unfortunately, I'm running in to complications of what is feasible on Android and power efficient.

Initial Design: Originally, I've been thinking and implementing the following
  • Embedded Device: Constantly in discoverable mode, creates a service with an RFCOMM server running to accept multiple connections.
  • Android Phone: Listen for Broadcast intents that would tell me when the embedded device (discoverable) is nearby, and then create an RFCOMM client socket to it.

The difficulty I am having with this design is that I do not get intents when I would expect them. Even if I turn the embedded device on and cycle the Android phone's Bluetooth adapter to off/on ... none of these Broadcast intents are received:

The only thing that seems to work is to periodically either have the phone try to connect to the Bluetooth device's RFCOMM socket, or to periodically trigger Bluetooth scans (both power inefficient). This will trigger ACTION_FOUND and ACTION_ACL_CONNECTED. If i shutdown the embedded device, I will receive ACTION_ACL_DISCONNECTED. The issue, again, is that none of these are received if I do not explicitly have the phone try to initiate a socket connection. This is bad for power efficiency on the phone.


Do I have this logic backwards? Should the embedded device keep track of Bluetooth MAC addresses that it has paired with and be the RFCOMM client, whereas the Android application creates a service and is the RFCOMM server just hanging around and waiting for a connection? This seems logically backwards, though... I wouldn't think the Android phone would create a service or be the server to make this happen.

If I go in to my car, it almost immediately manages to establish a connection with my phone. So, I know this is possible!

The concrete questions I have are two-fold: 1) Is there something I am doing wrong with my "initial design" to make it more effective, and 2) Is the 2nd logic I propose what things like cars use to establish quick communication and poll frequently? (since the battery power of the car is not a concern...). I am thinking of putting a server on the Android app that the Embedded device just tries to keep connecting to, and when successful, it's used as a notification to the Android app to try and connect to the embedded device's server. That would keep most current structure in place.
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