ESP32 S2 mini

• Board summary
  • Specifications
• ESPHome support
• Pinout
  • Interfaces
  • Notes on I²C on the S2 Mini
• Enter bootloader mode to program over USB
• References

Board summary

Specifications

I have some boards that say ESP32-S2FH4 on the chip (which should have 4 MB flash, and no PSRAM), though the official Wemos docs⁶ says they should have ESP32-S2FN4R2. The silkscreen prints match and have v1.0.0 on the backside (but without the white background). There are some reports from others that have also gotten supposed Wemos ESP32 S2 Mini boards with S2FH4 instead of S2FN4R2 -- so these might actually be counterfeits.

ESPHome support

Board config:

esp32:
  board: lolin_s2_mini
  variant: ESP32S2
  framework:
    type: esp-idf

Config for status_led (on GPIO15):

light:
  - platform: status_led
    name: "Status LED"
    id: esp_status_led
    icon: "mdi:alarm-light"
    restore_mode: ALWAYS_OFF
    pin:
      number: GPIO15
      inverted: false

Pinout

Interfaces

The ESP32 S2 Mini board has 2x I²C buses, 4x SPI, 8x PWM channels, 2x ADCs, 2x 8-bit DAC, 2x UART channels, 1x I²S bus and an USB OTG interface⁸.

Unsafe pins (strapping pins, trigger bootloader modes if pulled up/down):

• GPIO0 (Button 0): SPI boot mode, pull-up.
• GPIO45: VDD_SPI voltage, defaults as pull-down $0V$.
• GPIO46: SPI boot mode, pull-down.

Other notes about pins

• GPIO33: I²C SCL (schematic)
• GPIO35: I²C SDA (schematic)
• GPIO17: DAC_1
• GPIO18: DAC_2
• GPIO11-GPIO20 (ADC2): Not usable when Wi-Fi is enabled⁹.
• VBUS: is VIN or $VDD$, directly connected to $+$ on the USB-C connector. Max input voltage is $6V$⁷.
• Power supply for GPIO33, GPIO34, GPIO35, GPIO36 and GPIO37 is configurable to be either VDD3P3_CPU (default) or VDD_SPI.
• GPIO10, GPIO34: FSPI/SPI CS0 (Chip select).
• GPIO12, GPIO36: FSPI/SPI CLK (Clock).
• Supports LEDC PWM from esp-idf¹¹.
• The ESPHome ledc component only supports using GPIO0-GPIO33¹².
• For pin mappings used by the arduino framework¹³, see pins_arduino.h.

Notes on I²C on the S2 Mini

According to the datasheet any GPIO pins can be used for the I²C bus. But then the schematic shows:

• GPIO33: SDA
• GPIO35: SCL

It seems that the datasheet is "more correct", and that it is in fact possible to use any GPIO pins for I²C (though GPIO33 and GPIO35 might be handling I²C on the hardware level, other pins might be using them on the software level?).

Using I²C with the esp-idf framework, you might see errors like:

[C][i2c.idf:061]: I2C Bus:
[C][i2c.idf:062]:   SDA Pin: GPIO16
[C][i2c.idf:063]:   SCL Pin: GPIO18
[C][i2c.idf:064]:   Frequency: 50000 Hz
[C][i2c.idf:073]:   Recovery: failed, SDA is held low on the bus

The i2c component in esp-idf has two undocumented¹⁴ parameters, sda_pullup_enabled and scl_pullup_enabled, that can be used to enable or disable the internal $10k\Omega$ pullout resistors. By default, they are enabled on GPIO33 and GPIO35, and according to the datasheet from Espressif, the S2 Mini has both internal pull-up and pull-down resistors on all GPIO pins.

To use pins other than GPIO33 and GPIO35, you need to disable or enable these internal pull-up resistors. Weather you need to enable or disable them seem to depend on what device you are connecting. For an PN532 RFID/NFC reader, you need to disable them:

i2c:
  sda_pullup_enabled: false
  scl_pullup_enabled: false

Then you can configure any GPIO pins for I²C:

i2c:
  - id: i2c_bus0
    sda: GPIO33
    scl: GPIO35
    sda_pullup_enabled: false
    scl_pullup_enabled: false

This also works well with YAML anchors and the ESPHome !include syntax if you use packages. You can specify defaults for the i2c components, and then using the above you can override them in the file importing it.

I'm unsure why datasheet says that any pins can be used for I²C when the schematic shows GPIO33 and GPIO35 being wired as SDA and SCL, maybe it's done in software or software/firmware can bridge other GPIO pins to the internal system pins for I²C on the chip.

Side-note: Sometimes, for some components, it can help to set the frequency to $400kHz$ for the I²C bus.

Enter bootloader mode to program over USB

To put the ESP32 S2 Mini into bootloader mode:

1. Unplug USB/power
2. Hold both buttons (Marked RST and 0)
3. Plug in USB
4. Release RST ("reset")
5. Release 0 ("boot")

This puts the device into boot loader mode where it can be flashed. On Linux it appears as /dev/ttyACM0 (or higher number if 0 already exists). On Mac OS it shows up as /dev/tty.usbmodem01 and /dev/cu.usbmodem01.

On systems with AppArmor, it gets in the way and disrupts the access ("protocol error")

Useful tool: Adafruit ESPTool only works on Chrome. Can be used to erase memory.

Erase memory with esptool.py:

$ esptool.py --port COM13 erase_flash

Flashing my bootstrap config on Mac OS, with esph.py:

$ esph.py run esp32-s2-mini --name study-VINDRUTA --user --domain s21.sudo.is --device /dev/tty.usbmodem01

Or using esphome directly:

$ esphome -s node_name $namee -s lower_node_name $hostname -s domain $domain run esp32-s2-mini.yaml --device /dev/tty.usbmodem0

Some incomplete answers online that I stitched this together from:

press both buttons and release programming button, s2 mini set for programming¹⁵

hold 0, press reset, release 0¹⁶

Be careful to not accidentally break one of the buttons off the board.

References