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HX710: Python class for the HX710 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 methods are GPIO and PIO, because they deal properly with the conversion ready signal resulting in a more precise result.

Constructor

hx710 = HX710(clock_pin, data_pin, mode=1)

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. mode is the setting of the load cell amplifier. The default value of 1 also selects the external sensor.

hx710 = HX710(clock_pin, data_pin, mode=1, 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. mode is the setting of the load cell amplifier. The default value of 1 also selects the external sensor. The argument state_machine has to be set to different values if more than one HX711 device is used by an application.

hx710 = HX710(clock_pin, data_pin, spi, mode=1)

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. mode is the of of the load cell amplifier. The default value of 1 also selects the external sensor.

Methods

hx710.set_mode(mode)

Sets the mode which is used for the next call of hx710.read()

result = hx710.read()

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

result = hx710.read_average(times=3)

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

result = hx710.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 = hx710.set_time_constant(value=None)

Set the time constant used by hx710.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 = hx710.get_value()

Returns the difference of the filtered load cell value and the offset, as set by hx710.set_offset() or hx710.tare()

units = hx710.get_units()

Returns the value delivered by hx710.get_value() divided by the scale set by hx710.set_scale().

hx710.tare(times=15)

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

hx710.power_down()

Set the load cell to sleep mode.

hx710.power_up()

Switch the load cell on again.

Examples

# Example for Pycom device, gpio mode
# Connections:
# Pin # | HX710
# ------|-----------
# P9    | data_pin
# P10   | clock_pin
#

from hx710 import HX710
from machine import Pin

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

hx710 = HX710(pin_SCK, pin_OUT)

hx710.tare()
value = hx710.read()
value = hx710.get_value()

# Example for micropython.org device, gpio mode
# Connections:
# Pin # | HX710
# ------|-----------
# 12    | data_pin
# 13    | clock_pin
#

from hx710 import HX710
from machine import Pin

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

hx710 = HX710(pin_SCK, pin_OUT)

hx710.tare()
value = hx710.read()
value = hx710.get_value()

# Example for micropython.org device, RP2040 PIO mode
# Connections:
# Pin # | HX710
# ------|-----------
# 12    | data_pin
# 13    | clock_pin
#

from hx710_pio import HX710
from machine import Pin

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

hx710 = HX710(pin_SCK, pin_OUT)

hx710.tare()
value = hx710.read()
value = hx710.get_value()

# Example for Pycom device, spi mode
# Connections:
# Pin # | HX710
# ------|-----------
# P9    | data_pin
# P10   | clock_pin
# None  | spi clock
#

from hx710_spi import HX710
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 = HX710(pin_SCK, pin_OUT, spi)

hx710.tare()
value = hx710.read()
value = hx710.get_value()

# Example for micropython.org device, spi mode
# Connections:
# Pin # | HX710
# ------|-----------
# 12    | data_pin
# 13    | clock_pin
# 14    | spi clock

from hx710_spi import HX710
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 = HX710(pin_SCK, pin_OUT, spi)

hx710.tare()
value = hx710.read()
value = hx710.get_value()