ESP32-C3 Super Mini

This is my new favorite microcontroller board whenever space is restricted. This tiny board fits even into the smallest devices and still provides ten fully usable GPIOs.

It is compatible with all ESP32 development environments, ESPHome, and you can directly upload open-source firmware made for ESP32, like WLED.

Here is an example that shows how you can use the ESP32 C3 SuperMini and a 8x8 WS2812 LED Panel to create an awesome colorful light cube - without any programming and just three short wires:

Overview

The ESP32 C3 SuperMini is energy efficient, widely available and very affordable, and both its computational power and its 4MB flash size are more than sufficient for most DIY projects. I have replaced Arduinos and ESP8266 with this board in most of my new projects.

When more than 10 GPIOs are needed, or when a dual core is required for computational intense tasks, I typically choose the ESP32-S2 Mini. I tend to use classic ESP32S only when I need full backwards compatibility, i.e. when using third party firmware that isn’t yet available for the newer ESP32 family members.

Here are the ESP32 C2 SuperMini benefits:

• Compact: very small (22.5x18mm)
• Easy To Use: works out of the box with many environments like platform.io or ESPHome. There are no issues with entering firmware upload mode, and no fiddling with pressing “boot” buttons to select the right mode.
• Low Power: low power consumption, supports Bluetooth BLE, making it ideal for battery-operated devices
• Shields: battery shields are available that add battery charging and portable power supply to the C3 Super Mini
• Affordable: typically available for under €1.50

GPIOs

The board has a USB-C connector and 10 freely usable GPIOs. Four GPIOs can be used as analog input:

Programmable Blue LED

A programmable blue LED is connected to GPIO 8 (inverted: low active), and a red power LED is on when the board is connected to 5V (using its internal voltage regulator). This red LED is off when you power the board directly via the 3.3V pin, i.e. from a battery. This makes sense to conserve energy when power is limited.

Conclusion

While it is more than twice as fast as a ESP8266, it is a single core controller running at 160MHz clock speed. Classic ESP32S are dual-core running at 240MHz and are roughly three times as fast. That said, most DIY projects do not require such speeds, and speed comes at cost: power consumption. If your project does involve very computing-intense tasks or needs to respond in real-time to more than one task, you may want to use a classic ESP32S or its successor ESP32-S3.

Its very small form factor limits the number of exposed GPIOs. If 10 GPIOs are not enough, you may have to look into larger boards that provide the room for exposing up to 22 GPIOs.

Caveat: Defective Board Designs

While this board is readily available from many sellers, there are subtle differences in board layout. In 2024, board designs started to occasionally surface that may cause issues with WiFi connectivity:

On the left, you see the “normal” board design, and on the right the “revised” layout. In the new layout, the crystal clearly has moved closer to the ceramic WiFi antenna.

WiFi Sending Impaired

Users of the new board report that while they can receive WiFi networks, connecting to WiFi networks was impossible or took very long. Other users reported that connection required physically touching the antenna. Others experienced connectivity issues when female pin headers were added, especially when pin 21 was wired.

All observations indicate interference during WiFi transmission, most probably caused by the relocation of the crystal closer to the antenna: once transmission power is reduced (i.e. by touching the antenna), the problem went away. Likewise, once pin headers were installed, and once wires were connected to pin 21 (closest to antenna), this increased field strengths and aggrevated the interference.

Remedy

While you can safely use the defective boards for many taks not involving WiFi, a workaround to make the board transmit correctly is to reduce the transmission power by code, i.e. via WiFi.setTxPower(WIFI_POWER_8_5dBm);. Reducing the transmission power prevents the interference from reaching critical levels.

By reducing the WiFi transmission power, you coincidentally reduce the overall power consumption, and since the lower transmission power is still sufficient for most home environments with decent WiFi coverage, this does not need to be a bad thing.

This workaround may be impractical when your C3 SuperMini needs to operate in weak WiFi environments or far away from your access points (i.e. in the garden) in which case you should return defective boards.

The vast majority of C3 SuperMini use a flawless board design. Apparently, only selected charges of this board were affected by a “redesign”. If in doubt, you can measure the distance between the crystal and the ceramic antenna (see image above). There should be a gap of at least 1mm. Affected boards show a gap of just 0.3mm. Here is a more in-depth article describing the hardware differences.

Performance

ESP32 C3 SuperMini is a great replacement for ESP8266 and more than doubles its processing speed. It also comes with a solid voltage regulator (most ESP8266 ship with under-rated voltage regulators that easily brown out once you connect power-hungry external sensors).

Here is a quick performance comparison:

GPIO

The ESP32-C3 has 22 GPIOs of which the C3 Super Mini exposes 13 due to its compact size. Of these 13 GPIO, 10 are freely usable whereas the remaining 3 GPIOs are strapping pins and cannot be used during the boot procedure.

All GPIOs are multifunctional and can be configured for various purposes, such as digital I/O, ADC (Analog-to-Digital Converter), UART, SPI, I2C, PWM, and more.

Ten Freely Usable GPIOs

These 10 GPIO can be freely used:

Additional Three GPIOs

If you require more GPIOs, then these three GPIOs can be used with some restrictions: make sure your circuitry isn’t pulling any of these up or down by hardware.

Since these strapping pins are only used during boot (when your firmware isn’t yet active), you can use them freely in your softwaee (firmware). Justu make sure your wiring doesn’t tamper with their state. Else, your board may not boot properly.

JTAG is available on GPIO4-GPIO7.

Interfaces

Boot Modes

The strapping pins control the boot behavior during the boot process:

Board Schematics

Programmable LED

The board has a blue LED connected to GPIO8. This LED is inverted because it is sinked, not sourced: low turns the LED on, and high turns it off.

Programming

The ESP32-C3 Super Mini is widely adopted and simple to use.

platformio

In platformio, use the board ESP32-C3-DevKitM-1.

[env:esp32-c3-devkitm-1]
platform = espressif32
board = esp32-c3-devkitm-1

More specialited IDs like lolin_c3_mini may work even better:

[env:lolin_c3_mini]
platform = espressif32
board = seeed_xiao_esp32c3

ESPHome

In ESPHome configurations, use the board id esp32-c3-devkitm-1:

esp32:
  board: esp32-c3-devkitm-1

You can adjust and override specs if needed:

esphome:
  name: c3-supermini-test
  friendly_name: C3 SuperMini Test
  platformio_options:
    board_build.f_flash: 40000000L
    board_build.flash_mode: dio
    board_build.flash_size: 4MB

esp32:
  board: esp32-c3-devkitm-1
  variant: esp32c3
  framework:
    type: arduino

light:
  - platform: status_led
    name: "Status LED"
    id: esp_status_led
    icon: "mdi:alarm-light"
    pin:
      number: GPIO8
      inverted: true
    restore_mode: ALWAYS_OFF

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^{_{(content created Aug 28, 2024 - last updated Dec 11, 2024)}}