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HX711: Python class for the HX711 load cell

This is a very short and simple class. This lib includes three variants of the module. One is using direct GPIO pin handling, the other uses the PIO module of the RPI Pico. The third variant uses SPI. Besides the class instantiation, all variants offer the same methods. The preferred variants are GPIO and PIO, because they deal properly with the conversion ready signal resulting in a more precise result.

Constructor

hx711 = HX711(clock_pin, data_pin, gain=128)

This is the GPIO constructor. data_pin and clock_pin are the pin objects of the GPIO pins used for the communication. clock_pin must not be an input-only pin. gain is the setting of gain and channel of the load cell amplifier. The default value of 128 also selects channel A.

hx711 = HX711(clock_pin, data_pin, gain=128, state_machine=0)

This is the Raspberry Pi PIO constructor. data_pin and clock_pin are the pin objects of the GPIO pins used for the communication. gain is the setting of gain and channel of the load cell amplifier. The default value of 128 also selects channel A. The argument state_machine has to be set to different values if more than one HX711 device is used by an application.

hx711 = HX711(clock_pin, data_pin, spi, gain=128)

This is the SPI constructor. data_pin is the SPI MISO, clock_pin the SPI MOSI. These must be Pin objects, with data_pin defined for input, clock_pin defined as output. They must be supplied in addition to the spi object, even if spi uses the same pins for miso and mosi. spi is the SPI object. The spi clock signal will not be be used. gain is the setting of gain and channel of the load cell amplifier. The default value of 128 also selects channel A.

Methods

hx711.set_gain(gain)

Sets the gain and channel configuration which is used for the next call of hx711.read()

Gain Channel
128 A
64 A
32 B

result = hx711.read()

Returns the actual raw value of the load cell. Raw means: not scaled, no offset compensation.

result = hx711.read_average(times=3)

Returns the raw value of the load cell as the average of times readings of The raw value.

result = hx711.read_lowpass()

Returns the actual value of the load cell fed through an one stage IIR lowpass filter. The properties of the filter can be set with set_time_constant().

rh = hx711.set_time_constant(value=None)

Set the time constant used by hx711.read_lowpass(). The range is 0-1.0. Smaller values means longer times to settle and better smoothing. If value is None, the actual value of the time constant is returned.

value = hx711.get_value()

Returns the difference of the filtered load cell value and the offset, as set by hx711.set_offset() or hx711.tare()

units = hx711.get_units()

Returns the value delivered by hx711.get_value() divided by the scale set by hx711.set_scale().

hx711.tare(times=15)

Determine the tare value of the load cell by averaging times raw readings.

hx711.power_down()

Set the load cell to sleep mode.

hx711.power_up()

Switch the load cell on again.

Examples

# Example for Pycom device, gpio mode
# Connections:
# Pin # | HX711
# ------|-----------
# P9    | data_pin
# P10   | clock_pin
#

from hx711 import HX711
from machine import Pin

pin_OUT = Pin("P9", Pin.IN, pull=Pin.PULL_DOWN)
pin_SCK = Pin("P10", Pin.OUT)

hx711 = HX711(pin_SCK, pin_OUT)

hx711.tare()
value = hx711.read()
value = hx711.get_value()

# Example for micropython.org device, gpio mode
# Connections:
# Pin # | HX711
# ------|-----------
# 12    | data_pin
# 13    | clock_pin
#

from hx711 import HX711
from machine import Pin

pin_OUT = Pin(12, Pin.IN, pull=Pin.PULL_DOWN)
pin_SCK = Pin(13, Pin.OUT)

hx711 = HX711(pin_SCK, pin_OUT)

hx711.tare()
value = hx711.read()
value = hx711.get_value()

# Example for micropython.org device, RP2040 PIO mode
# Connections:
# Pin # | HX711
# ------|-----------
# 12    | data_pin
# 13    | clock_pin
#

from hx711_pio import HX711
from machine import Pin

pin_OUT = Pin(12, Pin.IN, pull=Pin.PULL_DOWN)
pin_SCK = Pin(13, Pin.OUT)

hx711 = HX711(pin_SCK, pin_OUT, state_machine=0)

hx711.tare()
value = hx711.read()
value = hx711.get_value()

# Example for Pycom device, spi mode
# Connections:
# Pin # | HX711
# ------|-----------
# P9    | data_pin
# P10   | clock_pin
# None  | spi clock
#

from hx711_spi import HX711
from machine import Pin, SPI

pin_OUT = Pin("P9", Pin.IN, pull=Pin.PULL_DOWN)
pin_SCK = Pin("P10", Pin.OUT)

spi = SPI(0, mode=SPI.MASTER, baudrate=1000000, polarity=0,
             phase=0, pins=(None, pin_SCK, pin_OUT))

hx = HX711(pin_SCK, pin_OUT, spi)

hx711.tare()
value = hx711.read()
value = hx711.get_value()

# Example for micropython.org device, spi mode
# Connections:
# Pin # | HX711
# ------|-----------
# 12    | data_pin
# 13    | clock_pin
# 14    | spi clock

from hx711_spi import HX711
from machine import Pin

pin_OUT = Pin(12, Pin.IN, pull=Pin.PULL_DOWN)
pin_SCK = Pin(13, Pin.OUT)
spi_SCK = Pin(14)

spi = SPI(1, baudrate=1000000, polarity=0,
          phase=0, sck=spi_SCK, mosi=pin_SCK, miso=pin_OUT)

hx = HX711(pin_SCK, pin_OUT, spi)

hx711.tare()
value = hx711.read()
value = hx711.get_value()