Blues Cygnet™ Datasheet: Cygnet v1.2
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
- 
Features of the ST STM32L433CC microcontroller
- 
80MHz Clock speed
 - 
256KB Flash, proprietary code readout protection
 - 
64KB of SRAM including 64KB with hardware parity check
 - 
Ultra-low-power with FlexPowerControl
 - 
11x timers
 - 
16x communication interfaces
 - 
14-channel DMA controller
 - 
Rich analog peripherals (independent supply)
 - 
True random number generator
 
 - 
 - 
Compliant with the Adafruit Feather Specification
- 
Includes a USB-C port for easy power and serial connectivity
 - 
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.
 
 - 
 - 
USER_BTNprogrammable button - 
LED_BUILTINprogrammable LED (red) - 
JTAG (SWD capable) debug jack
 - 
BOOT and RESET buttons
 - 
Modular design supports Feather pins or an expansion PCB (to break pins out to 0.1" headers for easier wiring and debugging).
 - 
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