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Selecting a Board

TL;DR

If you insist on wiring up the hardware yourself instead of using an integrated solution, acquire an ESP32-S3 DevKit Board with a N16R2 type of module.

Definitions and Background

  • There are variants of the ESP32 series other than ESP32 and ESP32-S3. OpenDTU-OnBattery is mostly concerned with the aforementioned two types.
  • SoC Chip or MCU or SoC: Refers to the ESP32(-S3) silicon chip in a plastic package without any PCB or external components.
    • This part determines whether you are using an ESP32 or an ESP32-S3.
    • Example part numbers: ESP32-U4WDH, ESP32-S3, ESP32-S3R2, or ESP32-S3FH4R2.
    • Some chips have integrated flash and/or PSRAM, while others do not.
    • Details can be found in the ESP32 datasheet, ESP32-S3 datasheet, or even the ESP32-S3 Technical Reference Manual.
    • These parts are manufactured by Espressif.
    • A popular cosumer product integrating these chips directly are Shelly devices.
  • Module Module: Refers to an assembled part consisting of an ESP32(-S3) chip and external components, soldered onto a PCB, and hidden under an RF shield.
    • Example part numbers: ESP32-WROOM-32U, ESP32-S3-WROOM-1-N4, or ESP32-S3-WROOM-2-N16R8V.
    • Many modules add SPI flash memory and/or PSRAM, which are external to the SoC.
    • Details can be found in the respective datasheets (non-exhaustive list): ESP32-WROOM-32, ESP32-WROOM-32D/U, ESP32-S3-WROOM-1, or ESP32-S3-WROOM-2.
    • These modules are orginally manufactured by Espressif, but there are compatible knock-off products advertised under identical part numbers.
    • Using these modules simplifies integration into custom applications. Popular consumer products using these modules are ESP32-based relay boards.
  • Module Board or PCB: Refers to the PCB which integrates an ESP32(-S3) module with a power supply, USB connector(s), pin headers, and more components to facilitate practical use of the module.
    • Example parts: ESP32-DevKitC, ESP32-S3-DevKitC-1, OpenDTU Fusion.
    • Espressif originally manufactured the aforementioned development kits, which became a de facto standard for hobbyists. Third party manufacturers sell compatible boards using identical names.

Flash Memory

Due to the growing size of the firmware binaries, an ESP32 module with at least 8 MB of flash memory is required to be able to use OTA updates. You may run OpenDTU-OnBattery on ESP32-based boards with only 4 MB of flash memory, but you will have to update the firmware on these boards using the USB connection, i.e., physical access is required.

ESP32 vs. ESP32-S3

You should prefer an ESP32-S3 (note the "S3"). The ESP32-S3 has more GPIOs (not all may be pinned out) and a slightly more efficient core. More importantly, it has native USB support, freeing one hardware UART.

ESP32-S3 Board

ESP32-S3 Reserved Pins

ESP32-S3 modules with 8 MB of PSRAM use an octal SPI interface. On these modules, pins GPIO 35, 36, and 37, which are usually wired to the board's pin header, are in use for the internal communication between ESP32-S3 and PSRAM. Therefore, these pins are not available for external use, even though they are wired to the board's pin header.

Use a board which integrates one of the following modules:

ESP32-S3-WROOM-... Flash PSRAM Antenna
...1U-N16R8 16 MB 8 MB external
...1-N16R8 16 MB 8 MB PCB Trace
...1U-N16R2 16 MB 2 MB external
...1-N16R2 16 MB 2 MB PCB Trace
...1U-N16 16 MB - external
...1-N16 16 MB - PCB Trace
...1U-N8R8 8 MB 8 MB external
...1-N8R8 8 MB 8 MB PCB Trace
...1U-N8R2 8 MB 2 MB external
...1-N8R2 8 MB 2 MB PCB Trace
...1U-N8 8 MB - external
...1-N8 8 MB - PCB Trace
...2-N16R8V 16 MB 8 MB PCB Trace
...2-N32R8V 32 MB 8 MB PCB Trace

Make sure that the board actually uses the native USB capability, such that the third hardware UART becomes available. There are boards with two USB connectors, where one connectnatively to the ESP32. In that case, the board is fine. On board with only one USB connector, look out for a USB to UART transceiver. If there is one on the board, the chip is possibly not connected natively to the USB port.

16 MB of Flash Memory

You will not be able to leverage 16 MB of flash memory with OpenDTU-OnBattery any time soon. However, given the price difference, you might want to go for a version with 16 MB, allowing the module/board to be reused in a different project eventually.

ESP32-S3 Pricing