ESP32 Mini or ESP8266 Soil Moisture Sensor

Code

This is the code to insert into ESPHOME after creating the sensor. The first part is generated automatically; you only need to copy the section after “captive_portal:”

esphome:

  name: soil-humidity-sensor

  friendly_name: soil humidity sensor

esp8266:

  board: esp01_1m

# Enable logging

logger:

# Enable Home Assistant API

api:

  encryption:

    key: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

ota:

  - platform: esphome

    password: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

wifi:

  ssid: !secret wifi_ssid

  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails

  ap:

    ssid: "soil-humidity-sensor"

    password: "xxxxxxxxxxxx"

captive_portal:

sensor:

  # Analog hygrometer sensor configuration

  - platform: adc

    pin: A0           # Analog pin A0 on D1 Mini

    name: "Soil Humidity"

    unit_of_measurement: "%"

    accuracy_decimals: 1

    update_interval: 10min  # Update frequency

     filters:

      - calibrate_linear:

         - 3.3 -> 0.0          # In air

         - 0.1 -> 100.0      # Moderately humid soil

deep_sleep:

  run-duration: 120s

  sleep_duration: 1200s

If the sensor fails to wake up due to signal loss, I added this sensor as a “Package” to resolve the issue

Package name “soil_humidity_sensor.yaml”

Part to copy into the created Package:

sensor:
  - platform: template
    sensors:
      stable_soil_humidity:
        value_template: >
          {% if states('sensor.soil_humidity_sensor_soil_humidity') not in ['unavailable', 'unknown', 'none'] %}
            {{ states('sensor.soil_humidity_sensor_soil_humidity') | float(0) }}
          {% else %}
            {{ states('sensor.stable_soil_humidity') | float(0) }}
          {% endif %}
        friendly_name: "Stable Soil Humidity"
        unit_of_measurement: "%"

Update

For those experiencing issues with “deep sleep” where the sensor is no longer detected, this alternative can be used. “Modem Sleep” deactivates the WiFi module only when not in use, but keeps the ESP8266 active. This consumes slightly more power but prevents disconnection issues

This is the other variant:

esphome:

  name: soil-humidity-sensor

  friendly_name: soil humidity sensor

esp8266:

  board: esp01_1m

# Enable logging

logger:

# Enable Home Assistant API

api:

  encryption:

    key: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

ota:

  - platform: esphome

    password: "xxxxxxxxxxxxxxxxxxxxxxxxxx"

wifi:

  ssid: !secret wifi_ssid

  password: !secret wifi_password

  power_save_mode: LIGHT  # Activates power saving for WiFi

  # Enable fallback hotspot (captive portal) in case wifi connection fails

  ap:

    ssid: "soil-humidity-sensor"

    password: "xxxxxxxxxxxx"

captive_portal:

sensor:

  # Soil humidity sensor configuration

  - platform: adc

    pin: A0  # Analog pin A0 on D1 Mini

    name: "Soil Humidity"

    unit_of_measurement: "%"

    accuracy_decimals: 1

    update_interval: 10min  # Update frequency

    filters:

      - calibrate_linear:

          - 3.3 -> 0.0    # Value in air (dry)

          - 0.1 -> 100.0  # Value in humid soil

interval:

  - interval: 5min

    then:

      - lambda: |-

          static int wifi_fail_count = 0;

          if (!wifi::global_wifi_component->is_connected()) {

            ESP_LOGW("wifi", "WiFi not connected! Attempting to reconnect...");

            wifi::global_wifi_component->retry_connect();

            wifi_fail_count++;

          } else {

            wifi_fail_count = 0;  // Reset del contatore se la connessione torna

          }

          if (wifi_fail_count >= 2) {  // Dopo 2 tentativi falliti (10 minuti)

            ESP_LOGE("wifi", "WiFi not reconnecting, restarting device...");

            ESP.restart();

          }

Update

For those encountering issues with ESP8266, I have modified the base to accommodate an ESP32 mini. This is slightly longer and a bit wider, but offers a more stable WiFi connection. I am also including the modified code for this model.

esphome:

  name: soil-humidity-sensor

  friendly_name: soil humidity sensor

esp32:

  board: esp32dev

  framework:

    type: arduino

# Enable logging

logger:

# Enable Home Assistant API

api:

  encryption:

    key: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

ota:

  - platform: esphome

    password: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

wifi:

  ssid: !secret wifi_ssid

  password: !secret wifi_password

  # Enable fallback hotspot (captive portal) in case wifi connection fails

  ap:

    ssid: "Soil-Humidity Fallback Hotspot"

    password: "xxxxxxxxxxxxxx"

captive_portal:

sensor:

  - platform: adc

    pin: GPIO36  # Corrected for ESP32

    name: "Soil Humidity"

    unit_of_measurement: "%"

    accuracy_decimals: 1

    update_interval: 10s  # Update less frequently to save energy

    attenuation: 11db  # Expands ADC range to 0-3.9V to avoid saturation

    filters:

      - calibrate_linear:

          - 3.0 -> 0.0    # Dry (in air)

          - 0.95 -> 100.0   # Very humid soil

      - lambda: |-

          if (x < 0) return 0;

          if (x > 100) return 100;

          return x;

      - median:

          window_size: 5

          send_every: 3

          send_first_at: 1

deep_sleep:

  run_duration: 180s   # Active for 3 minutes

  sleep_duration: 1200s  # Deep sleep for 20 minutes

Electrical connections

The battery pack is connected directly to the TP4056 charging module on the B+/B- pads

The solar panel is also connected to the TP4056 module's input on the pads next to the USB-C port + and -

The output of the charging module OUT+/OUT- is connected directly to the ESP32 mini module on the 3V3 and GND pins

The humidity sensor is connected to the ESP32 mini module for power: VCC pin to 3V3 pin, GND pin to GND pin, and AUOT pin to GPIO36 pin

The GPIO26 and RST pins of the ESP32 mini module must be connected together if you want to use the deep sleep function, which will allow the dev-board to execute code at regular intervals and then enter power-saving mode

Essentially, the connections should be made on the innermost pins (the white ones). See pinout diagram

Update

For those who wish to monitor battery voltage, I am providing the connection diagram, which shows two 100K resistors connected on one side to GPIO34 pin, and on the other side, one resistor connected to GND-OUT- and the other to the positive of the OUT+ charging module

I am attaching the new code, where if you need to adjust the correct voltage value in case of imprecise readings, simply vary this parameter: multiply: 2.0

esphome:
 name: soil-humidity
 friendly_name: Soil humidity

esp32:
 board: esp32dev
 framework:
   type: arduino

logger:

api:
 encryption:
   key: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

ota:
 - platform: esphome
   password: "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

wifi:
 ssid: !secret wifi_ssid
 password: !secret wifi_password
 power_save_mode: light

 ap:
   ssid: "Soil-Humidity Fallback Hotspot"
   password: "ElmXWDJFu3p5"

captive_portal:

sensor:
 - platform: adc
   pin: GPIO36
   id: umidita_suolo
   name: "Soil Humidity"
   unit_of_measurement: "%"
   accuracy_decimals: 1
   attenuation: 11db
   update_interval: 10s
   filters:
     - calibrate_linear:
         - 3.00 -> 0.0
         - 0.95 -> 100.0
     - lambda: |-
         if (x < 0.0) return 0.0;
         if (x > 100.0) return 100.0;
         return x;
     - median:
         window_size: 5
         send_every: 3
         send_first_at: 1

 - platform: adc
   pin: GPIO34
   id: battery_volt
   name: "Battery Voltage"
   unit_of_measurement: "V"
   accuracy_decimals: 2
   attenuation: 11db
   update_interval: 10s
   filters:
     - multiply: 2.0
     - median:
         window_size: 5
         send_every: 3
         send_first_at: 1

 - platform: template
   name: "Battery"
   id: batteria_percento
   unit_of_measurement: "%"
   accuracy_decimals: 0
   update_interval: 10s
   lambda: |-
     float v = id(battery_volt).state;
     if (isnan(v)) return NAN;
     if (v >= 4.20) return 100.0;
     if (v <= 3.00) return 0.0;
     return ((v - 3.00) / (4.20 - 3.00)) * 100.0;

binary_sensor:
 - platform: status
   name: "Soil Humidity Status"

deep_sleep:
 run_duration: 180s
 sleep_duration: 1200s