With the help of four weight sensors (load cells), the HX711 module measures the weight of the object placed on the scale (water balloon, gas bottle) and sends it to the smart home system via NodeMCU WIFI.
On the 3D-printed scale, the four load cell sensors snap into place exactly. the HX711 module and NodeMCU need to be glued in place with double-sided adhesive.
Four pairs of 6mm diameter and 3mm thick magnets can be glued to the two halves of the 3D-printed scale, which hold the two halves of the scale together. This is optional.

ESPHome sensor code:
sensor:

  - platform: hx711

    name: "Balloon"

    dout_pin: GPIO1

    clk_pin: GPIO14

    gain: 128

    update_interval: 60s

    unit_of_measurement: l

    icon: "mdi:water-outline"

    device_class: "water"

    state_class: "measurement"

    accuracy_decimals: 2

    filters:

      - calibrate_linear:

          - 213200 -> 0

          - 561100 -> 19

      - clamp:

          min_value: 0

          max_value: 20

          ignore_out_of_range: false

      - round: 2