OpenPM01

Free/Libre and open-source firmware for the FRME-PM-01A power meter.

Hardware notice: The FRME-PM-01A hardware is designed by @FrostAutumn and licensed under CC-BY-NC-SA 3.0. OpenPM01 is an independent firmware project and is not affiliated with nor endorsed by the original hardware project.

Features

• Real-time voltage, current, power, coulomb counter (mAh), temperature, and humidity
• Coulomb integration via trapezoidal rule
• Battery state-of-charge gauge (voltage-to-percentage lookup with progress bar, low-voltage warning)
• Visual alerts (blinking) for under/over-voltage, over-current, and temperature limits
• High refresh rate
• Four orientation modes: portrait, portrait 180° flipped, landscape, landscape flipped
• Built on libopencm3 — no STM32 HAL, no proprietary blobs, fully free-software stack
• Catppuccin color themes (Mocha / Macchiato / Frappé / Latte)

Screenshots

Portrait / Landscape

Both orientations support 180° flip for flexible panel mounting.

Portrait	Landscape

Color themes

Mocha	Macchiato

Frappé	Latte

Build

# Requires PlatformIO
platformio run

# Upload via CMSIS-DAP
platformio run --target upload

Orientation

Pick exactly one orientation flag in build_flags (default: UI_PORTRAIT):

-DUI_PORTRAIT           # portrait
-DUI_PORTRAIT_FLIP      # portrait 180° flipped
-DUI_LANDSCAPE          # landscape
-DUI_LANDSCAPE_FLIP     # landscape flipped

Color theme

-DCATPPUCCIN_MOCHA
-DCATPPUCCIN_MACCHIATO
-DCATPPUCCIN_FRAPPE
-DCATPPUCCIN_LATTE

Battery gauge

Enabled by default with 4S LiFePO₄ profile. Switch profile or disable:

-DBATTERY_4S_LIFEPO4    # 4S LiFePO₄ (default, can be omitted)
-DNO_BATTERY            # disable battery gauge entirely

Add new battery profiles by adding an #elif block in common.h that defines bat_lut, BAT_LUT_LEN, and BAT_LO_V.

Pin Map

Function	Pin	Peripheral
ST7789 SDA (MOSI)	PA6	Software SPI
ST7789 SCL (SCK)	PA7	Software SPI
ST7789 DC	PA4	GPIO
ST7789 RST	PA5	GPIO
ST7789 CS	PA3	GPIO
ST7789 BLK	PA2	GPIO (active-low)
INA226 SDA	PB7	I2C1
INA226 SCL	PB6	I2C1
SHT30 SDA	PB8	Software I2C
SHT30 SCL	PB9	Software I2C

Project Structure

src/
├── main.c                   Scheduler + init
├── ui.c                     UI rendering
├── sensors.c                INA226 + SHT30 data hub
├── ina226.c                 Hardware I2C1 driver
├── sht30_sm.c               SHT30 state machine
├── st7789_stm32_spi.c       Display driver (software SPI)
└── fonts/                   11× Cascadia Code Nerd Font (18–38 px)

include/
├── common.h                 Constants, colors, helpers
├── ui.h                     Display API
├── sensors.h                Sensor accessor API
├── colour.h                 Catppuccin theme palette
├── ina226.h
├── sht30_sm.h
├── st7789_stm32_spi.h
└── fonts/                   Font headers + bitmap_typedefs.h

Credits

Hardware

This firmware targets the FRME-PM-01A hardware designed by @FrostAutumn, licensed under CC-BY-NC-SA 3.0.

Open-source dependencies

Component	Author	License
stm32f1_st7789_spi	Avra Mitra	MIT
INA226 library	Rob Tillaart	MIT
SHT30 library	LibDriver	MIT
libopencm3	libopencm3 project	LGPLv3
Caskaydia Cove (Cascadia Code fork)	Eli Heuer / Microsoft	SIL OFL 1.1

License

OpenPM01 firmware is released under GNU GPLv3.

Hardware license notice

The FRME-PM-01A hardware design is licensed under CC-BY-NC-SA 3.0 by @FrostAutumn. The original author has additionally expressed an intent to restrict unauthorized derivatives beyond what the SA clause itself requires.

OpenPM01 was written entirely from scratch and does not reference the original hardware project's firmware, which has not been open-sourced.

GPLv3 grants you the freedom to use, modify, and distribute this firmware, provided you comply with its terms. However, the GPLv3 license governs this firmware only. If you intend to use this firmware commercially or in any derived work, note that the hardware design remains subject to its CC-BY-NC-SA 3.0 terms — please ensure compliance with the original hardware license independently.