nodemcu-firmware/docs/modules/hx711.md

HX711 Module

Since	Origin / Contributor	Maintainer	Source
2015-10-09	Chris Takahashi	Chris Takahashi	hx711.c
2019-04-20	Philip Gladstone	Philip Gladstone

This module provides access to an HX711 load cell amplifier/ADC. The HX711 is an inexpensive 24bit ADC with programmable 128x, 64x, and 32x gain. The standard Chinese sources have cheap HX711 boards for around $1.

This can be used for single shot reads, or repetitive reads.

Note: To save ROM image space, this module is not compiled into the firmware by default.

hx711.init()

Initialize io pins for hx711 clock and data.

Syntax

hx711.init(clk, data)

Parameters

• clk pin the hx711 clock signal is connected to
• data pin the hx711 data signal is connected to

Returns

nil

Example

-- Initialize the hx711 with clk on pin 5 and data on pin 6
hx711.init(5,6)

hx711.read()

Read digital loadcell ADC value.

Syntax

hx711.read(mode)

Parameters

• mode ADC mode. This parameter specifies which input and the gain to apply to that input. Reading in mode 1 or 2 takes longer than reading in mode 0.

mode	channel	gain
0	A	128
1	B	32
2	A	64

Returns

a number (24 bit signed ADC value extended to the machine int size)

Example

-- Read ch A with 128 gain.
raw_data = hx711.read(0)

hx711.start()

Starts to read multiple samples from the ADC.

Syntax

hx711.start(mode, samples, callback)

Parameters

• mode ADC mode. This parameter is currently ignored and reserved to ensure backward compatibility if support for additional modes is added.
• samples The number of samples before the callback is invoked. The length of time depends on the chip's sampling rate.
• callback The callback is invoked with three arguments (see below).

mode	channel	gain
0	A	128
1	B	32
2	A	64

Returns

nothing

Callback

This is invoked every time samples samples are read from the HX711. The arguments are:

• A string which contains samples packed 24 bit values. This can be unpacked with the struct module (using the "i3" format).
• The time in microseconds of the reception of the last sample in the buffer.
• The number of samples dropped before the start of this buffer (after the end of the previous buffer).

Notes

This api only is built if GPIO_INTERRUPT_ENABLE and GPIO_INTERRUPT_HOOK_ENABLE are defined in the user_config.h. This is the default.

Also, do not try and mix calls to start and calls to read. Any calls to read will implicitly call stop first.

Example

-- Read ch A with 128 gain.
hx711.start(0, 2, function(s, t, d) local r1, r2, _ = struct.unpack("i3 i3", s) print(r1, r2) end)

hx711.stop()

Stops a previously started set of reads. Any data in buffers is lost. No more callbacks will be invoked.

Syntax

hx711.stop()

Returns

nothing