# Unable to send Notes with Adafruit Feather nRF52840 express

**URL:** <https://discuss.blues.com/t/unable-to-send-notes-with-adafruit-feather-nrf52840-express/3479>\
**Category:** Notecarrier F\
**Created:** [February 28, 2026, 10:18pm UTC](https://discuss.blues.com/t/unable-to-send-notes-with-adafruit-feather-nrf52840-express/3479 "2026-02-28T22:18:26Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ssykes](https://avatars.discourse-cdn.com/v4/letter/s/97f17d/32.png) [@ssykes](https://discuss.blues.com/u/ssykes)\
**Post date:** [February 28, 2026, 10:18pm UTC](https://discuss.blues.com/t/unable-to-send-notes-with-adafruit-feather-nrf52840-express/3479/1 "2026-02-28T22:18:27Z")

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I’m having trouble with submitting a Note to the Blues Hub. A link to a working example would probably help.

Hardware Setup:

Host MCU: Adafruit Feather nRF52840 Express

Notecard Carrier: Notecarrier-F v1.3 (Feather socket)

Notecard: NOTE-WBNAN (LTE-M/NB-IoT)

LoRa Radio: Adafruit LoRa FeatherWing (RFM95W 915 MHz)

Physical Configuration:

LoRa FeatherWing → Feather nRF52840 Express → Notecarrier-F → Notecard

————————————————————————————————————

What Works:

Notecard detected on I2C at address 0x17

I2C scan finds Notecard successfully

LoRa reception works perfectly (RSSI -47 dBm, packets received every 30 seconds)

What Fails:

Writing JSON commands to Notecard fails with I2C error 3 (NACK on data)

————————————————————————————————————

Example code that fails:

char json[] = “{\“req\”:\“note.add\”,\“file\”:\“events.qo\”,\“body\”:{\“node\_id\”:1}}”;

Wire.beginTransmission(0x17);

Wire.write(0x00);

for (int i = 0; json[i]; i++) {

```auto
Wire.write(json\[i\]);

```

}

Wire.write(0x00);

byte error = Wire.endTransmission();

// Returns: error = 3 (NACK on data)

-------------------------------------------------------------------------

Also Tried:

I2C clock speeds: 10 kHz, 100 kHz, 400 kHz (all fail)

Waiting for Notecard to be ready before write (times out after 1 second)

Different JSON formats (all fail with error 3)

-------------------------------------------------------------------------

I2C scan

Scanning I2C bus (0x01-0x7F)…

Found device at 0x17

Found 1 device(s)

Scan again in 5 seconds…

-------------------------------------------------------------------------

Environment:

Arduino IDE Version: 2.3.8

Date: 2026-02-25T15:38:21.789Z

CLI Version: 1.4.1

Copyright © 2026 Arduino SA

Board Package: Adafruit nRF52 by Adafruit v1.7.0

Board: Adafruit Feather nRF52840 Express

Blues Library: blues-minimal-i2c v0.0.4

RadioLib: v6.6.0

————————————————————————————————————

POWER SETUP:

- Feather nRF52840: Powered by USB

- Notecard: Powered by 3.7V LiPo battery connected to Notecarrier-F

SAME RESULT WITH:

- Feather nRF52840: Powered by USB

- Notecarrier-F: Powered by USB

SYMPTOMS:

- Blues Notehub has connected in the past it showed repeated brown-out resets

- I2C communication fails immediately after power-on

- Notecard becomes unresponsive (timeout waiting for ready state)

QUESTION:

Could insufficient battery current be causing the Notecard to

brown-out during I2C communication? What power supply do you

recommend for testing?

————————————————————————————————————

Reference:

According to Blues documentation, this hardware combination is tested and supported:

"Tested Notecard Outboard Firmware Update MCUs:

Adafruit Feather nRF52840 Express"

Source: [Notecarrier Datasheet - Notecarrier F v1.3](https://dev.blues.io/datasheets/notecarrier-datasheet/notecarrier-f-v1-3/)

Questions:

Is there a known I2C compatibility issue between nRF52840 TWI peripheral and Notecard?

Which Blues library should be used for nRF52840? (blues-minimal-i2c, Blues official library, or different version?)

Are there specific I2C settings required for nRF52840? (pull-up resistor values, clock speed, timing?)

Is there working example code for Feather nRF52840 + Notecarrier-F?

Could this be a hardware issue with my Notecarrier-F or Notecard?

---

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**Author:** ![RobLauer](https://sea2.discourse-cdn.com/flex020/user_avatar/discuss.blues.com/roblauer/32/1567_2.png) [@RobLauer](https://discuss.blues.com/u/RobLauer)\
**Post date:** [March 2, 2026, 6:12pm UTC](https://discuss.blues.com/t/unable-to-send-notes-with-adafruit-feather-nrf52840-express/3479/3 "2026-03-02T18:12:11Z")

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Hi @ssykes and welcome to the Blues community!

I believe using the appropriate [Blues-supported firmware library](https://dev.blues.io/tools-and-sdks/firmware-libraries/) will resolve these issues for you. We do have this doc about [using Notecard without a library](https://dev.blues.io/guides-and-tutorials/notecard-guides/notecard-communication-without-a-library/#notecard-communication-without-a-library), but we’ve done a lot of work to alleviate the issues presented in our SDKs.

Thanks,  
Rob