Cygnet is a low-cost embeddable STM32L4+-based microcontroller board designed to accelerate the development and deployment of battery-powered IoT solutions.

As a lower-cost alternative to the Swan, Cygnet still provides an extensive feature set required for edge-based inferencing and remote monitoring applications. Like its more expensive sibling, Cygnet is designed to be the ideal companion to Notecard while offering a more budget-friendly option.
Functional Description
Cygnet is a Feather-compatible STM32-based MCU, and a lower-cost alternative to our popular Swan MCU. Like the Swan, Cygnet is offered in a Feather standard form factor and uses a STM32L4 part while still providing plenty of flash and RAM to run the majority of your Notecard-powered applications.
Features
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Features of the ST STM32L433CC microcontroller
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80MHz Clock speed
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256KB Flash, proprietary code readout protection
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64KB of SRAM including 64KB with hardware parity check
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Ultra-low-power with FlexPowerControl
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11x timers
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16x communication interfaces
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14-channel DMA controller
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Rich analog peripherals (independent supply)
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True random number generator
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Compliant with the Adafruit Feather Specification
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Includes a USB-C port for easy power and serial connectivity
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Includes a PMIC accessible via a JST PH connector, allowing you to either power the board via a LiPo battery and/or recharge the battery via USB.
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USER_BTNprogrammable button -
LED_BUILTINprogrammable LED (red) -
JTAG (SWD capable) debug jack
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BOOT and RESET buttons
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Modular design supports Feather pins or an expansion PCB (to break pins out to 0.1" headers for easier wiring and debugging).
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10kΩ pull-ups on the
SDAandSCLpins -
Qwiic connector
Package Configuration
The Cygnet can be used as a Feather-compatible board with soldered male headers, as a part of the Blues Notecard Feather dev kit.
Feather-compatible Cygnet
Out of the box, the Cygnet is usable as a Feather-compatible device.

Pin Information
The following tables contain pin definition mappings between the Cygnet Feather pins to the STM32L433 core MCU.
Cygnet Feather to STM32 Mapping
| Pin # | Pin Name | Pin # | Pin Name | |
|---|---|---|---|---|
| RST | RST# | ---- | ||
| 3V3 | ---- | |||
| AREF | ---- | |||
| GND | ---- | |||
| PA0 | A0 | BAT | ||
| PA1 | A1 | PH0 | EN | |
| PA2 | A2 | PB3 | USB | |
| PA3 | A3 | PB4 | D13 | |
| PB1 | A4 | PB15 | D12 | |
| PA7 | A5 | PB0 | D11 | |
| PA5 | CK | PB13 | D10 | |
| PB5 | MO | PB14 | D9 | |
| PA6 | MI | PB9 | D6 | |
| PA10 | RX | PB8 | D5 | |
| PA9 | TX | PB6 | SCL | |
| PH3 | B | PB7 | SDA | |
| PC13 | USER_BTN | PA8 | LED_BUILTIN |
Pin Description Table
| Pin Name | Pin Description (Primary) | Voltage Tolerance |
|---|---|---|
| A0 | I/O - GPIO, PWM, ADC | 5V |
| A1 | I/O - GPIO, PWM, ADC | 5V |
| A2 | I/O - GPIO, PWM, ADC | 5V |
| A3 | I/O - GPIO, PWM, ADC | 3.6V |
| A4 | I/O - GPIO, PWM, ADC | 5V |
| A5 | I/O - GPIO, ADC | 5V |
| D5 | I/O - GPIO | 5V |
| D6 | I/O - GPIO | 5V |
| D9 | I/O - GPIO, PWM | 5V |
| D10 | I/O - GPIO, ADC | 5V |
| D11 | I/O - GPIO, PWM, ADC | 5V |
| D12 | I/O - GPIO, PWM, ADC | 5V |
| D13 | I/O - GPIO, ADC | 5V |
| SCL | I²C - Serial Clock | 5V |
| SDA | I²C - Serial Data | 5V |
| 3V3 | Power - Constant 3.3V Supply | - |
| EN | Power - Chip Enable | 5V |
| GND | Power - Ground | - |
| RST | Power - Reset | - |
| BAT | Power - Battery Voltage Supply | - |
| AREF | Power - Reference Voltage | - |
| USB | Power - USB Voltage Supply | - |
| RX | Serial - Receive | 5V |
| TX | Serial - Transmit | 5V |
| B | Boot0 - Boot into Bootloader | 5V |
| MI | SPI - Main In Secondary Out | 5V |
| MO | SPI - Main Out Secondary In | 5V |
| CK | SPI - Serial Clock, DAC | 3.6V |
| ENABLE_3V3 | Enable External 3V3 Regulator | - |
| LED_BUILTIN | Built-in LED | - |
| USER_BTN | User Button | - |
NOTE: All digital I/O pins are interrupt capable.
Specifications
Electrical Characteristics
DC Characteristics
| Description | Minimum | Maximum | Unit |
|---|---|---|---|
VIN Supply Voltage | 2.5 | 5.5 | V |
VBAT Supply Voltage | 2.5 | 5.5 | V |
VUSB Supply Voltage | 2.5 | 5.5 | V |
| Supply Current | 0.5 | 2.0 | A |
3V3 Output @ 5V | 1.07 | 2.09 | A |
Absolute Maximum Ratings
| Description | Minimum | Maximum | Unit |
|---|---|---|---|
| Operating temperature | -40 | 125 | °C |
Ordering Information
- Please visit the Cygnet product page for ordering information.
Design Files
Open source hardware designs for the Swan and all Blues Hardware are maintained in the note-hardware GitHub repository.
Board Errata
- The on-board QWIIC connector should only be used when the
ENABLE_3V3signal is HIGH and thus powering the 3V3 pin, as it is by default.
Terms and Conditions
Visit Blues Hardware Terms & Conditions.
Revision History
| Author | Date | Summary |
|---|---|---|
| Alex R. Bucknall | 10 DEC 2024 | Document drafted |
| Brandon Satrom | 03 FEB 2025 | Added Errata for ENABLE_3V3 |
Contact Information
For other questions about the Cygnet, visit the Blues Forum.
Blues Inc.
https://blues.com
50 Dunham Ridge Suite 1650
Beverly, MA 01915
support@blues.com