BLE Central Arduino Example

[WALLTECH]

Hi Neil, as posted on the ESP-Arduino repo, a BLE Central scan for device, connect, enable notifications or other characteristic and read/write the value example would be really useful.

[nkolban]

Howdy John ... noticed and received. Lets see if we can't get specific on what you'd like to see so that we can deliver the example as close as possible to what you want. As we see here, there is ambiguity in phrases like central and peripheral, so I'm going to spell out what I think you'd like to see and then see how close this comes to what you actually want.

You want the ESP32 to be a "client" in that it will perform a scan for a "server" that is continually broadcasting. When it finds a suitable server, it will then connect to that server, enable notifications and start receiving notifications from the server. In addition, the ESP32 will want to read the value of the characteristic and write a new value at any given time.

Is that correct? When you confirm or tweak, we'll start writing the sample for your review.

[WALLTECH]

Hi Neil, wow, that's very kind, thank you. I'm sorry I couldn't help more, I wanted to try to contribute to the examples. Your description is exactly right in every way! It will also make a wonderful central example.

[nkolban]

Okly dokly ... on it my friend.

[WALLTECH]

I'd be writing Hex byte arrays if that helps

[nkolban]

A first pass at a full BLE Client application running in Arduino has been made available here:

https://github.com/nkolban/esp32-snippets/tree/master/cpp_utils/tests/BLETests/Arduino/BLE_client

The paint is still wet on it and there may very well be problems but built and tested on my system and so far so good. What I'd like you to do is run up the application and give it a whirl.

You will need an external BLE Server such as the nRF Connect application. The sample expects a BLE Server with an exposed service with UUID of 91bad492-b950-4226-aa2b-4ede9fa42f59 that exposes a characteristic with UUID 0d563a58-196a-48ce-ace2-dfec78acc814. These are just generated UUIDs but what your server uses and what your client expects must match. The sample does a few things:

1. It scans for a suitable advertised server.
2. It connects to the server.
3. It downloads from the server the value of the characteristic at the start and logs it.
4. Every second, it writes a new value of the characteristic to the server.
5. If the server issues a notification, the client detects that and logs that a notification occurred.

That's a lot of function. Usually much more than we put in a "sample". Please have a read of the code and then we can start the discussions on how much is understandable and work together to make what isn't clear clearer for the next person.

[WALLTECH]

It looks great! I'll throw in my uuids and give it a go tomorrow. Thank you very much, this is a great help.

[WALLTECH]

Alright, I put my uuids in and set it up to connect by mac address rather than service as the ones I want aren't advertised, and I get this out with no further data:

Found our device! address: e9:44:8b:41:d7:2d
Forming a connection to e9:44:8b:41:d7:2d

• Created client
  E (49918) BT: l2cble_start_conn_update, the last connection update command still pending.
  E (49918) BT: l2cble_start_conn_update, the last connection update command still pending.
• Connected to server
  E (50267) BT: l2cble_start_conn_update, staus = 1, line = 509
  E (50755) BT: set_read_value unformat.len = 18
  The characteristic value was:
  E (51039) BT: bta_gattc_cmpl_cback unknown conn_id = 3, ignore data

[nkolban]

Howdy John,
I'm studying now. If you can learn/use IRC, find me on channel #ESP32 for live chat.

[nklys]

Hello Neil. When a server is detected, the following error occurs and a cyclic reboot.

ets Jun 8 2016 00:22:57

rst:0x1 (POWERON_RESET),boot:0x17 (SPI_FAST_FLASH_BOOT)
configsip: 0, SPIWP:0xee
clk_drv:0x00,q_drv:0x00,d_drv:0x00,cs0_drv:0x00,hd_drv:0x00,wp_drv:0x00
mode:DIO, clock div:1
load:0x3fff0010,len:4
load:0x3fff0014,len:588
load:0x40078000,len:0
load:0x40078000,len:9768
entry 0x400789b8
Starting Arduino BLE Client application...
BLE Advertised Device found: Name: , Address: 63:03:2a:64:67:33, serviceUUID: 91bad492-b950-4226-aa2b-4ede9fa42f59
Found our device! address: Forming a connection to 63:03:2a:64:67:33

• Created client
  E (37489) BT: l2cble_start_conn_update, the last connection update command still pending.
  E (37489) BT: l2cble_start_conn_update, the last connection update command still pending.
• Connected to serverGuru Meditation Error: Core 0 panic'ed (Unhandled debug exception)
  Debug exception reason: Stack canary watchpoint triggered (Btc_task)
  Register dump:
  PC : 0x4000c3fa PS : 0x00060536 A0 : 0x800da0fa A1 : 0x3ffde0b0
  A2 : 0x3ffd6479 A3 : 0x3ffd647b A4 : 0xfffffffe A5 : 0x00000000
  A6 : 0x3ffd8ae8 A7 : 0x3ffd1ce6 A8 : 0x00005ce7 A9 : 0x3ffdc160
  A10 : 0x000000a5 A11 : 0x00060f23 A12 : 0x00060d23 A13 : 0x3ffde250
  A14 : 0x02336764 A15 : 0x02336764 SAR : 0x00000018 EXCCAUSE: 0x00000001
  EXCVADDR: 0x00000000 LBEG : 0x400014fd LEND : 0x4000150d LCOUNT : 0xfffffffe

Backtrace: 0x4000c3fa:0x3ffde0b0 0x400da0f7:0x3ffde0d0 0x400da4b1:0x3ffde0f0 0x400da575:0x3ffde120 0x400da585:0x3ffde140 0x400d6222:0x3ffde160 0x400d3d0a:0x3ffde180 0x400d3fdd:0x3ffde210 0x400f2336:0x3ffde230 0x400ef188:0x3ffde2b0

Rebooting...

[nkolban]

Howdy,
Can you paste bin your code and point out the line at which the crash is happening. I have seen this before when using the BLE Server (not client) and the solution was to add a 200msec delay after initialization. I have a "gut feel" that the same thing may be happening with the client. If you can post your sketch, I'll take a good look.

[nklys]

This is your example BLE_cient.ino. And as a server NRF connect.

[nklys]

Where do I need to add a delay? After BLEDevice :: init ("") ?