The Lifex ESP32-Tux-Mini Offers a Tiny Path to Energy-Harvesting Experimentation with an ESP32-C3
Available under a reciprocal open hardware license, this compact board pulls in power to charge a lithium-polymer battery.
Pseudonymous Swiss maker "Lifex" has designed a compact development board built around Espressif's ESP32-C3 system-on-chip and boasting an integrated energy harvesting circuit designed to keep a 3.7V lithium-polymer battery topped-up from solar or other sources.
"This is an ESP32-C3 board I created for building a sensor cube," Lifex explains of the project. "To make it (more or less) energy independent a energy harvesting circuit with the [Texas Instruments] BQ25504 chip is added. The board can be powered with a 3.7V LiPo battery which is charged by a small solar cell."
TI's BQ25504 is an ultra-low-power boost converter with integrated battery management, designed to sit between a lithium-ion or lithium-polymer battery or super-capacitor (supercap) and charge it from a range of sources of harvestable energy — primarily solar cells, but also things like radio-frequency energy, heat, and even movement, providing the right harvesting hardware is added. "As far as I have seen," Lifex claims, "it's the only ESP32 board with an energy harvesting circuit on it."
In Lifex's design, the energy-harvesting chip is there to feed a 3.7V battery which in turn powers an Espressif's ESP32-C3 — a pin-compatible replacement for the popular ESP8266 which marked Espressif's first-ever part to use the free and open source RISC-V architecture for a central processor, a single-core 32-bit microcontroller running at up to 160MHz and with 400kB of static RAM (SRAM).
While the ESP32-C3 itself offers 22 general-purpose input/output (GPIO) pins, Lifex's board is focused on a small footprint to fit in with a planned "sensor cube" creation — meaning only nine of the pins are externally accessible, along with a hardware UART. A further tenth GPIO pin is brought out to an on-board WS2812B addressable RGB LED.
Design files for the board, dubbed the ESP32-Tux-Mini, are available on GitHub under the reciprocal GNU General Public License 3; pre-assembled boards can be purchased from Lifex's Tindie store at $15 each.