ESP32C3 and intermittent BLE connection

Products & Technology Bluetooth Low Energy
1

Hi,
I’ve been working for some time developing a special timer for model aircraft - it uses an onboard xiao_esp32C3 which receives a string of flight parameters to initiate a flight. This information is sent by an Android app via BLE.
I’d got it all working quite nicely with my phone - but when I tried a friend’s phone, it simply would not connect. The ESP would seem to pair, but the app was unable to find it when scanning.
I then had problems connecting with my phone - which until then had worked fine.
I’ve tried using a new ESP board, and sometimes the BLE connection works, sometimes not - I haven’t been able to establish a pattern, but the BLE connection seems to be randomly unreliable.
Apologies for the long post - any advice would be most welcome., thanks.

2

Hi there,

And Welcome Here…

Pretty good application for a BLE connection. Have you considered testing with the Nrf Connect for Desktops and a ($9) BLE dongle?
Great for that type of Diagnosis and many other applications , Like a BLE sniffer in Wireshark etc.
What mobile phones are we talking about? Not all support BLE , most are BT (classic) You can post the code or some snipt’s using the Code tags " </> " above , just paste it in there. makes it easy to read and you’ll get better quality help as well.

There are lots of BLE examples here so I encourage a look at those also. The C3 is slightly different in it’s interiors than the rest of the ESP line , so be aware.
Seems like the same application would benefit from an onboard IMU also like the Nrf52840 Sense Xiao. What is the data if I may ask, unless of course it is all proprietary. :grin:

HTH
GL :slight_smile: PJ :v:

3

Thanks for the swift response and suggestions. This widget is intended for use in small free flight (no radio control) model aircraft, and needs to be as small and light as possible, hence my choice of the C3. I will certainly look into nrf Connect, thanks. The data sent is just a stream of digits which are then sorted by the C3 into an array, defining the flight parameters and motor power setting. All that code is working fine - it’s just this intermittent connectivity that’s an issue. The Android app was written at MIT App inventor, following their examples, and mostly work ok on my Redmi Note (and others), but seems to fail on a Samsung Galaxy.
I’ve read that the C3 keeps a list of connected devices? Wondering if it’s possible to flush this - or something to restore the board to factory defaults.
Thanks again…

4

Hi there,

Sure thing, Yes I use MITAI 2 also with an app I built for control of a BLE locking device.(patent # US20230314907A1) using the Nrf52840 for battery life/power. There is a RTOS on the chip that will enter low power and may drop the connection for example if the code is not setup properly.
try rolling back to an older BSP first and retest.

then here are some things to consider…

  • The ESP-IDF-based Arduino core (used on ESP32-C3) runs BLE on a separate task. rollback suggestion
  • If user code (e.g. delay-heavy loops or blocking logic) runs on loop() or the main task and prevents BLE event handling, the stack gets starved.
  • Symptoms:
    • BLE doesn’t advertise consistently
    • BLE stops responding after a period
    • Pairing succeeds but no discovery

:hammer_and_wrench: Fix: Use non-blocking logic, or call delay(0) regularly to yield control, or run BLE in its own task (via xTaskCreatePinnedToCore()).

  • If the ESP32C3 BLE server advertises once and doesn’t restart advertising after disconnect, it won’t be discoverable to new phones.
  • Android can cache services, so sometimes you need to clear Bluetooth cache or reboot the phone.
BLEDevice::startAdvertising();  // Call this again on disconnect

From my experience, some will Argue with it , but for everything after it’s trash. If you want max stability for BLE on Xiao ESP32-C3:

  • Use ESP32 Arduino Core v2.0.7 or v2.0.8
  • Avoid ESP32 core v2.0.10 — known BLE issues
  • Avoid Serial prints inside BLE callbacks
  • Restart advertising after every disconnect
  • Minimize blocking code in loop()

HTH
GL :slight_smile: PJ :v:

also take a CLOSE look at the UUID’s and there Android friendliness…
NO serial prints in the Callbacks, will hang it…
Peripheral + Android Compatibility

  • BLE scan on Android is filtered by service UUID, device name, or address type.
  • If your Android app expects a service UUID but ESP isn’t advertising it properly — it’s invisible.
pAdvertising->addServiceUUID(myServiceUUID);

:grin:

5

Many thanks for that extensive response! There’s a lot to think about there, will be looking into it. Thanks again…

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6

Different Android phones have different BLE behavior, especially with background scanning and bonding.
Test with nRF Connect app (from Nordic) to verify if the ESP is discoverable and connectable.
If your device pairs but does not advertise properly, avoid pairing unless needed. Most BLE apps don’t need bonding/pairing.

7

More helpful advice, many thanks…

8

Few cents from my side:

I tried ESP32-C3 BLE with Arduino libraries (both BLE Device & Nimble). What I can say for sure is that I always was able to see the device advertising. Sometimes there was an issue pairing with the chip (I’ve only tried Windows PC), because Windows not always was able to pop-up the window to enter the security code (as I’ve incorporated some BLE security - authorization). But other than that no issues with the chip.
It is indeed possible to flush the paired/bonded devices list. Unfortunately, can’t tell for sure what is the command now, as it was long time ago.

Few remarks: Nimble is a lightweight library, so If you want to save some space on the device, I would suggest it.

I second PJ, EPS32-C3 is not a battery friendly chip, but if you don’t experience shortage on battery for your particular needs, I wouldn’t bother moving to another chip, like nrf52840. Especially, if it is just a hobby project. However, with the nrf52840 the consumption is 10 times less.

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