# HX711 Module | Since | Origin / Contributor | Maintainer | Source | | :----- | :-------------------- | :---------- | :------ | | 2015-10-09 | [Chris Takahashi](https://github.com/christakahashi) | [Chris Takahashi](https://github.com/christakahashi) | [hx711.c](../../app/modules/hx711.c)| | 2019-04-20 | [Philip Gladstone](https://github.com/pjsg) | [Philip Gladstone](https://github.com/pjsg) This module provides access to an [HX711 load cell amplifier/ADC](https://learn.sparkfun.com/tutorials/load-cell-amplifier-hx711-breakout-hookup-guide). The HX711 is an inexpensive 24bit ADC with programmable 128x, 64x, and 32x gain. The standard Chinese sources have [cheap HX711 boards](https://www.aliexpress.com/wholesale?SearchText=hx711+module) 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 ```lua -- 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 ```lua -- 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 ```lua -- 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