about broadcast (nrf52840, sdk15.0)

RE: about broadcast (nrf52840, sdk15.0)

Edvin — Tue, 17 Jul 2018 12:59:06 GMT

That is correct. To send exactly at the same time, you must use some proprietary radio protocol, such as the esb examples (which is a different protocol than BLE).

The disadvantage with this is that the esb devices has to be listening at the time when you are transmitting. This is possible, but it takes a lot more current than using BLE, because they have to have the radios on the entire time. That does not mean that you can't do it, but if the device runs on a battery, it will be drained faster.

Best regards,

Edvin

RE: about broadcast (nrf52840, sdk15.0)

lmouelo — Tue, 17 Jul 2018 09:38:33 GMT

ok thanks you and so to send exactly at the same time (broadcast) I can't use ble, I have to use the role of radio ?

RE: about broadcast (nrf52840, sdk15.0)

Edvin — Tue, 17 Jul 2018 09:33:22 GMT

The time between each communication event between the master/central and the slave/peripheral is called the connection interval. It is typically set near the top of the main.c file in our examples. The defines are:

MIN_CONN_INTERVAL

MAX_CONN_INTERVAL

and are given in units of 1.25 ms.

If you control both devices, central and peripheral, you can set MIN_CONN_INTERVAL = MAX_CONN_INTERVAL, and also equal in both of the devices. (The devices will disconnect if they can't agree on a connection interval).

The minimum allowed connection interval in BLE is 7.5ms ( = 4 units of 1.25ms).

I am not sure whether you will be able to squeeze 4 connections with a connection interval of 7.5ms on one central, but you can give it a go. 10ms should be fine I believe. Do some testing, and you will figure out pretty fast whether the connections will be maintained or not.

So a standard broadcast message is not possible in BLE. You can look into using the esb examples that we have, where several devices can listen on the same channel, and hence you can do broadcasting with this. Check out the examples:

SDK\examples\proprietary_rf\esb_prx

SDK\examples\proprietary_rf\esb_ptx

if you are interrested.

Best regards,

Edvin

RE: about broadcast (nrf52840, sdk15.0)

lmouelo — Tue, 17 Jul 2018 08:44:31 GMT

what is this time between each sends on the different peripherals?

it's always the same time ?

RE: about broadcast (nrf52840, sdk15.0)

lmouelo — Tue, 17 Jul 2018 08:16:20 GMT

okay so to send exactly at the same time (broadcast) I can't use ble, I have to use the radio role?

RE: about broadcast (nrf52840, sdk15.0)

Edvin — Tue, 17 Jul 2018 07:48:49 GMT

There is no such thing as "broadcast" in BLE. But you can forward the data to the 4 peripherals. The reason for why a broadcast doesn't work is because the central has a specific timeslot for each peripheral, where that peripheral will turn on the radio in receiver mode, and these timeslot do not overlap.

If you look into the examples:

SDK\examples\ble_central\ble_app_multilink_central for the central

and

SDK\examples\ble_peripheral\ble_app_blinky for the peripheral(s)

You can see that the central has a sort of "broadcast" where it sends a message to all of the peripherals on a button press. I say "broadcast" because it doesn't send one message that all the peripherals picks up at the same time, but it sends the message to each peripheral.

Best regards,

Edvin

RE: about broadcast (nrf52840, sdk15.0)

lmouelo — Tue, 17 Jul 2018 06:37:31 GMT

then I have a central card that receives data from 4 peripheral cards continuously and I want the central to send data once in a while to all peripheral cards at the same time (broadcast) as to receive the data, is this possible? thanks in advance

RE: about broadcast (nrf52840, sdk15.0)

Edvin — Mon, 16 Jul 2018 14:54:04 GMT

Hello,

What exactly do you mean with "broadcast mode"? A BLE beacon? Or advertisements in general?

Either way, this should be possible.

Please see this post.

I was a bit confused by your second post. I am not sure I quite understand what you mean with broadcast. Do you mean advertise? You can send advertisement packets, but the other devices will have to listen with their radio at that point in time. peripherals typically don't listen when they are not expecting any packets. You can do this, but listening like this takes a lot of power, and is not ideal for battery powered devices.

A better solution would be to send the message to the central, which can forward the packet to the other peripherals.

Peripherals works in a way that they turn off the radio when they are not using it. When they are in a connection, they will communicate with the other device when a connection interval has passed, and then turn it off again, until another connection interval has passed again. Hence they will not have their radio in listening mode and be able to hear advertising packets.

When two devices are in a connection, the messages are only meant for the device that it is connected to, and other BLE devices will not pick them up. The exception is advertising and scanning. Advertising is something a peripheral does to tell other devices that they are available for connection. Scanning is what the central does to pick up these advertising packets. Scanning is a more current consuming procedure, which is why phones often are the central in a connection.

Please let me know what you mean with broadcast mode. Maybe I misinterpreted what you meant.

Best regards,

Edvin

RE: about broadcast (nrf52840, sdk15.0)

lmouelo — Fri, 13 Jul 2018 13:43:18 GMT

Sorry, I'm correcting what I meant:
I have a central and 4 peripheral and the peripherals send data to the central, is it possible to parallel the central in central/broadcast