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
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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)
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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++) {
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
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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?
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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
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?