ESP8266 Multi Capacitive Soil Moisture Sensor

ESP8266 in combination with a eight port multiplexer to support up to 8 capacitive soil moisture sensors.

The esp8266 reads the sensors every 10 minutes, transfers the readings via MQTT to a broker and goes back to deep sleep. The MQTT messages and can be picked up by i.e. Home Assistant.

• Mode 1: USB powered
• Mode 2: Battery powered (optional solar)

The code is written in MicroPython.

Mode 1: USB powered

Parts required

• Wemos D1 mini Pro V2.0.0 ESP8266 4,56€
• Capacitive soil moisture sensor 0,61€
• CD4051 Multiplexer 1,85€
• Project box 0,72€
• Circuit board 1,66€
• Wires 1,90€
• Pin headers 0,88€
• 3D printed sensor case (order print at treatstock) ~1,20€

A usb charger and micro usb cable is assumed to be available.

Circuit diagram

Mode 2: Battery powered

Use more batteries in parallel if you want (a) to decrease the time between sensor readings or (b) prolong the time until the next charging cycle or (c) compensate for smaller solar panels.

The solar panel is optional, of course you can also charge the batteries manually with a charger once they are drained. If you use a solar panel, you need to connect it via the micro usb port to the esp8266

Note: the Wemos D1 mini Pro v2.0.0 already has a built-in charging module.

Additional parts required

• 18650 3,7V 3400mAh battery 2,21€
• JST connector 0,49€
• Optinal 5V 5W solar panel 4,13€

Circuit diagram

Setup

Configuration

Use the config.json to configure the esp8266 (no changes in boot.py or main.py required).

{
  "hostname": "NAME_OF_ESP8266",
  "wifi": {
    "ssid": "YOUR_WIFI_NAME",
    "password": "YOUR_WIFI_PASSWORD",
  },
  "mqtt": {
    "user": "MQTT_USER",
    "password": "MQTT_PASSWORD",
    "broker": "MQTT_BROKER_IP",
    "port": 1883,
    "topics": "TOPIC_NAME"
  }
}

Flashing Code to ESP8266

I prefer PyCharm and the respective MicroPython plugin. Nevertheless, you can use any other suitable editor.

Create a configuration for each of the three files and flash them onto the esp8266. You can use the MicroPython REPL to watch the execution of the programs:

Connecting to WiFi...connected
Connecting to MQTT...connected
Sending: {"analog": "481", "percent": "7", "updated": "07.02.2020 23:12:25"} 
Going back to sleep...

Home Assistant

Add i.e. two mqtt sensors to your sensors.yaml (your one esp8266 published to both topics as it operates multiple soil moisture sensors)

- platform: mqtt
  name: "Ficus Benjamina"
  state_topic: "esp8266/pflanzen-wohnzimmer-fenster/sensor0"
  value_template: "{{ value_json.percent }}"
  unit_of_measurement: "%"
  json_attributes_topic: "esp8266/pflanzen-wohnzimmer-fenster/sensor0"
  icon: mdi:leaf
- platform: mqtt
  name: "Zitronenbaum"
  state_topic: "esp8266/pflanzen-wohnzimmer-fenster/sensor1"
  value_template: "{{ value_json.percent }}"
  unit_of_measurement: "%"
  json_attributes_topic: "esp8266/pflanzen-wohnzimmer-fenster/sensor1"
  icon: mdi:fruit-citrus
- platform: mqtt
  name: "Balsamapfel"
  state_topic: "esp8266/pflanzen-wohnzimmer-fenster/sensor2"
  value_template: "{{ value_json.percent }}"
  unit_of_measurement: "%"
  json_attributes_topic: "esp8266/pflanzen-wohnzimmer-fenster/sensor2"
  icon: mdi:sprout

And the following to ui-lovelace.yaml to display the two sensors in the lovelace frontend (Custom multiple entities card is used in this example)

  - type: markdown
    style: !include /config/ui-lovelace/style/title.yaml
    content: Pflanzen

  - type: entities
    entities:
      - type: custom:multiple-entity-row
        entity: sensor.ficus_benjamina
        hide_state: true
        primary:
          entity: sensor.ficus_benjamina
          attribute: analog
          unit: ''
          name: 'Analog'
        secondary:
          entity: sensor.ficus_benjamina
          attribute: percent
          name: 'Wasser'
          unit: '%'
      - entity: sensor.zitronenbaum
        hide_state: true
        type: custom:multiple-entity-row
        primary:
          entity: sensor.zitronenbaum
          attribute: analog
          unit: ''
          name: 'Analog'
        secondary:
          entity: sensor.zitronenbaum
          attribute: percent
          unit: '%'
          name: 'Wasser'
      - entity: sensor.balsamapfel
        hide_state: true
        type: custom:multiple-entity-row
        primary:
          entity: sensor.balsamapfel
          attribute: analog
          unit: ''
          name: 'Analog'
        secondary:
          entity: sensor.balsamapfel
          attribute: percent
          unit: '%'
          name: 'Wasser'

Result in lovelace frontend:

Detail view:

Schematics

• Wemos D1 mini pro
• CD4051 Multiplexer

Build pictures

Two sensors placed in a plant each

Indoor case (source)

Outdoor case with top cover (source)

Three sensors connected to the esp (3 more available - multiplexer supports up to 8)

Front view of the connectors (the wholes could have been drilled better)

Micro usb power connected

VCC and GND JST connectors glued in place

6 analog pins (multiplexer channels) for 6 soil moisture sensors glued in place

Case prepared

Mode 1 completed without case and ability to connect 4 moisture sensors (2 more have been added after taking the picture)

Sleep pin soldered to be able to wake up from deep sleep

Wiring below esp8266 (not all connections are visible from the top)

Back with soldered connections

Multiplexer wired to headers for esp8266 without connectors for sensors

Back of esp8266 and multiplexer wiring

Capacitive soil moisture sensors protected with hot glue

Also pins at back are protected