Re: Can earphones be paired with two sound-producers at the same time, like the pc and the phone?

On 2/14/2022 9:43 AM, sms wrote:
> On 2/14/2022 1:40 AM, micky wrote:
>> This is the essential part of a longer post (soon to be released at
>> major theatres).
>>
>> This relates directly to cell phones.
>>
>> So to turn off the built-in PC speakers I disabled them but no sound
>> comes from the Bose bluetooth hearphones even though they are still
>> listed as paired with the PC, although the phone also says that the
>> hearphones are paired with it!!!
> 
> Paired but not connected.
> 
> It's possible to do what you want to do, but you need Bluetooth headphones with "multipoint" capability, you can't do it with standard Bluetooth headphones.
> 
> See <https://phiaton.com/collections/earphones/products/bt-100-nc>.

And the secret sauce is Bluetooth LE 4.1 .

https://microchipdeveloper.com/wireless:ble-phy-layer

    Channel Arrangement

    The 40 channels are divided into three advertising channels (Ch. 37, 38, and 39),
    and 37 data channels (Ch. 0-36).

    Advertising Channel Usage

     Device discovery
     Connection establishment
     Broadcast transmissions

    Data Channel Usage

     Bidirectional communication between connected devices
     Adaptive frequency hopping used for subsequent connection events

*******

The original Bluetooth is described this way.

    "Bluetooth uses a radio technology called frequency-hopping spread spectrum.
     Bluetooth divides transmitted data into packets, and transmits each packet
     on one of 79 designated Bluetooth channels. Each channel has a bandwidth of 1 MHz.
     It usually performs 1600 hops per second, with adaptive frequency-hopping
     (AFH) enabled.[23]

     Bluetooth Low Energy uses 2 MHz spacing, which accommodates 40 channels"

    "Bluetooth is a packet-based protocol with a master/slave architecture.

Further down

    "One master may communicate with up to seven slaves in a piconet. All devices
     within a given piconet use the clock provided by the master as the base
     for packet exchange. The master clock ticks with a period of 312.5 μs,
     two clock ticks then make up a slot of 625 µs, and two slots make up
     a slot pair of 1250 µs. In the simple case of single-slot packets, the
     master transmits in even slots and receives in odd slots. The slave, conversely,
     receives in even slots and transmits in odd slots. Packets may be 1, 3, or 5
     slots long, but in all cases, the master's transmission begins in even slots
     and the slave's in odd slots.

     The above excludes Bluetooth Low Energy, introduced in the 4.0 specification,
     [25] which uses the same spectrum but somewhat differently.
    "

It could be the three advertising channels, that help make
it possible for one slave to talk to two masters. But so far,
I don't see a description of how the advertising channels are
acquired for usage. The other 37 channels are used in a hopping
mode controlled by a master.

*******

https://devzone.nordicsemi.com/f/nordic-q-a/6411/can-two-masters-connect-two-slaves-at-the-same-time

   "Yes, you are correct, S110 7 (BLE peripheral/slave softdevice) can be in a
    connection and advertise in a non-connectable state simultaneously. But a
    BLE peripheral can not be in a connection with two centrals/masters simultaneously.

    However, with S110 8, a nRF51 peripheral/slave can be in a connection and
    advertise in scannable mode and receive RSSI signals from any centrals/masters
    in vicinity, therefore knowing of their presence. With that strategy, the peripheral
    could disconnect from master 1 and establish connection with master 2, or
    periodically alter connection between central 1 and central 2 and virtually
    have 2 connections to 2 centrals."

    [A "central" is just the politically correct synonym for "master" device]

   Paul