HX711 Load Cell Amplifier

The hx711 sensor platform allows you to use your HX711 load cell amplifier (datasheet, Sparkfun) with esphomelib

../../../_images/hx711-full.jpg

HX711 Load Cell Amplifier. Image by Sparkfun licensed and re-distributed under CC BY 2.0.

Connect GND to GND, VCC to 3.3V and the other three MISO (or SO for short), CS and CLOCK (or SCK) to free GPIO pins.

# Example configuration entry
sensor:
  - platform: hx711
    name: "HX711 Value"
    dout_pin: D0
    clk_pin: D1
    gain: 128
    update_interval: 15s

Configuration variables:

  • name (Required, string): The name for the load cell sensor.
  • dout_pin (Required, Pin Schema): The DOUT (or DAT) pin.
  • clk_pin (Required, Pin Schema): The CLK pin.
  • update_interval (Optional, Time): The interval to check the sensor. Defaults to 15s. See update_interval gotchas.
  • id (Optional, ID): Manually specify the ID used for code generation.
  • All other options from Sensor and MQTT Component.

Converting Units

As the HX711 does not have any calibration data, you have to convert the measurement to units yourself. To calibrate the sensor:

  1. Place nothing or a known mass on the sensor, for example 0kg
  2. Wait for the data to arrive in the logs and write down the value. For example 120.
  3. Place another (different) known mass on the sensor, for example 1kg
  4. Again wait for the data to arrive and note the value, for example 810.

Once you’ve done those steps, you can use the map function to map the incoming value to the calibrated one:

# Example configuration entry
sensor:
  - platform: hx711
    # ... Other HX711 options
    filters:
      - lambda: |-
          auto first_mass = 0.0; // first known mass was 0kg
          auto first_value = 120.0; // value for the first known mass was 120
          auto second_mass = 1.0; // second mass was 1kg
          auto second_value = 810.0; // second value was 810

          return map(x, first_value, second_value, first_mass, second_mass);
    unit_of_measurement: kg

Replace the masses and values 120.0, 810.0, etc with your values.