Discover the convenience of quick and dependable weight readings with HX711 and STM32G474RE
Elevate every ounce
Published Nov 08, 2024
Click board™
Load cell click
Dev Board
Nucleo 64 with STM32G474RE MCU
Compiler
NECTO Studio
MCU
STM32G474RE
Monitor and manage your health journey with reliable and consistent weight tracking
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Hardware Overview
How does it work?
Load Cell Click is based on the HX711, a specialized 24-bit analog-to-digital converter (ADC) designed for weight scale applications made by Avia Semiconductor. Among other sections, this device incorporates two high-resolution (24bit) A/D converters (ADC) with differential inputs and internal low-noise programmable gain amplifiers. Since the input voltages are very low, obtaining the best possible signal-to-noise ratio from the load cell connected to the input terminals is required. The load cell typically has four strain gauges, which are planar resistors and can change their resistance when compressed or stretched due to changes in their geometry. The load cell is typically a piece of metal with enough elasticity, resistant to material fatigue, so it can withstand many measurements before it has to be recalibrated. When a strain force is applied to the load cell, one pair of the strain gauges forming a Wheatstone bridge will become stretched, while the other pair will become compressed. The small voltage difference will appear across the bridge, proportional to the applied strain force. This voltage difference is in the mV range and can be measured and sampled to read the strain force intensity. Therefore, the load cell forms a transducer, directly translating the applied force to a voltage. As mentioned before, the main task of
the HX711 IC is to sample the voltage across the bridge as accurately as possible and with the least amount of noise. The Wheatstone bridge formed by strain gauges is attached to an excitation power source so that the resistance changes can be detected. The HX711 has a dedicated regulated voltage output, which provides the necessary excitation voltage. Two differential inputs connect the loads, offering various gain factors. The first differential input (labeled as A) offers a selectable gain of 64 X or 128 X. The second differential input (labeled as B) offers a fixed 32X gain factor. This offers the possibility to select the desired gain factor according to the used load cell and the magnitude of the strain force. Load Cell click offers serial communication utilizing the on-chip clock oscillator. The data output rate is selectable and depends on the logical state of the RTE pin routed to the mikroBUS™ CS pin. A HIGH logic level on this pin will set the output data rate at 80 samples per second (SPS), while the LOW logic level will set the data rate to 10 SPS. The serial communication of the HX711 IC is rather specific. When the data output pin (DO) goes to a LOW logic level, the host microcontroller (MCU) can start generating clock pulses on the SCK pin. The data is clocked out with the next 24 pulses, while the 25th clock pulse will set the DO pin to a HIGH logic level again.
After the DO pin goes LOW, the number of clock pulses is used to determine the gain level and the ADC channel for the next conversion. For example, if 27 pulses are applied after the DO pin goes to a LOW logic level, the next conversion will clock out the data from channel A with the gain amplifier (PGA) set to 64X. More information about the communication protocol can be found in the HX711 datasheet. However, the chip communication is taken care of in the library supplied with the Click board™, which contains simple-to-use functions, compatible with all MikroElektronika compilers. The SCK pin is also used to power down the IC: if the SCK pin stays HIGH for more than 60µs, the HX711 IC will enter power-down mode. As soon as the pin has been pulled to a LOW logic level (provided that the valid power supply is still present), the IC will power up again and reset the registers to their default values (Input A, PGA set to 128X). This Click board™ can operate with either 3.3V or 5V logic voltage levels selected via the VCC SEL jumper. This way, both 3.3V and 5V capable MCUs can use the communication lines properly. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.
Features overview
Development board
Nucleo-64 with STM32G474R MCU offers a cost-effective and adaptable platform for developers to explore new ideas and prototype their designs. This board harnesses the versatility of the STM32 microcontroller, enabling users to select the optimal balance of performance and power consumption for their projects. It accommodates the STM32 microcontroller in the LQFP64 package and includes essential components such as a user LED, which doubles as an ARDUINO® signal, alongside user and reset push-buttons, and a 32.768kHz crystal oscillator for precise timing operations. Designed with expansion and flexibility in mind, the Nucleo-64 board features an ARDUINO® Uno V3 expansion connector and ST morpho extension pin
headers, granting complete access to the STM32's I/Os for comprehensive project integration. Power supply options are adaptable, supporting ST-LINK USB VBUS or external power sources, ensuring adaptability in various development environments. The board also has an on-board ST-LINK debugger/programmer with USB re-enumeration capability, simplifying the programming and debugging process. Moreover, the board is designed to simplify advanced development with its external SMPS for efficient Vcore logic supply, support for USB Device full speed or USB SNK/UFP full speed, and built-in cryptographic features, enhancing both the power efficiency and security of projects. Additional connectivity is
provided through dedicated connectors for external SMPS experimentation, a USB connector for the ST-LINK, and a MIPI® debug connector, expanding the possibilities for hardware interfacing and experimentation. Developers will find extensive support through comprehensive free software libraries and examples, courtesy of the STM32Cube MCU Package. This, combined with compatibility with a wide array of Integrated Development Environments (IDEs), including IAR Embedded Workbench®, MDK-ARM, and STM32CubeIDE, ensures a smooth and efficient development experience, allowing users to fully leverage the capabilities of the Nucleo-64 board in their projects.
Microcontroller Overview
MCU Card / MCU
Architecture
ARM Cortex-M4
MCU Memory (KB)
512
Silicon Vendor
STMicroelectronics
Pin count
64
RAM (Bytes)
128k
You complete me!
Accessories
Click Shield for Nucleo-64 comes equipped with two proprietary mikroBUS™ sockets, allowing all the Click board™ devices to be interfaced with the STM32 Nucleo-64 board with no effort. This way, Mikroe allows its users to add any functionality from our ever-growing range of Click boards™, such as WiFi, GSM, GPS, Bluetooth, ZigBee, environmental sensors, LEDs, speech recognition, motor control, movement sensors, and many more. More than 1537 Click boards™, which can be stacked and integrated, are at your disposal. The STM32 Nucleo-64 boards are based on the microcontrollers in 64-pin packages, a 32-bit MCU with an ARM Cortex M4 processor operating at 84MHz, 512Kb Flash, and 96KB SRAM, divided into two regions where the top section represents the ST-Link/V2 debugger and programmer while the bottom section of the board is an actual development board. These boards are controlled and powered conveniently through a USB connection to program and efficiently debug the Nucleo-64 board out of the box, with an additional USB cable connected to the USB mini port on the board. Most of the STM32 microcontroller pins are brought to the IO pins on the left and right edge of the board, which are then connected to two existing mikroBUS™ sockets. This Click Shield also has several switches that perform functions such as selecting the logic levels of analog signals on mikroBUS™ sockets and selecting logic voltage levels of the mikroBUS™ sockets themselves. Besides, the user is offered the possibility of using any Click board™ with the help of existing bidirectional level-shifting voltage translators, regardless of whether the Click board™ operates at a 3.3V or 5V logic voltage level. Once you connect the STM32 Nucleo-64 board with our Click Shield for Nucleo-64, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.
Used MCU Pins
mikroBUS™ mapper
Take a closer look
Schematic
Step by step
Project assembly
Start by selecting your development board and Click board™. Begin with the Nucleo 64 with STM32G474RE MCU as your development board.
Track your results in real time
Application Output via Debug Mode
1. Once the code example is loaded, pressing the "DEBUG" button initiates the build process, programs it on the created setup, and enters Debug mode.
2. After the programming is completed, a header with buttons for various actions within the IDE becomes visible. Clicking the green "PLAY" button starts reading the results achieved with the Click board™. The achieved results are displayed in the Application Output tab.
Software Support
Library Description
This library contains API for Load Cell Click driver.
Key functions:
loadcell_read_results- Read results of functionloadcell_set_rate- Set rate functionloadcell_check_out- Check status of pin DO (do_pin)loadcell_reset- Reset clock functionloadcell_set_mode- Set clock mode functionloadcell_tare- Function of messure and read resultsloadcell_calibration- Calibration functionloadcell_get_weight- Get weight function
Open Source
Code example
This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.
/*!
* \file
* \brief Load cell Click example
*
* # Description
* Load cell click is a weight measurement click which utilizes a load cell element,
* in order to precisely measure the weight of an object.
* The Load Cell click can be used with the strain gauge type of load cells
* and can measure up to ±20V or ±40V of differential voltage.
*
* The demo application is composed of two sections :
*
* ## Application Init
* Initializes GPIO driver and performs the device reset,
* after which the next conversion cycle will be for channel B with 32 gate value.
* This function also selects the frequency of internal oscillator to 10Hz.
* Sets tare the scale, calibrate scale and start measurements.
*
* ## Application Task
* This is an example which demonstrates the use of Load Cell Click board.
* Display the measurement of scales in grams [ g ].
* Results are being sent to the Usart Terminal where you can track their changes.
* All data logs write on USB uart changes for every 1 sec.
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "loadcell.h"
// ------------------------------------------------------------------ VARIABLES
static loadcell_t loadcell;
static log_t logger;
loadcell_data_t cell_data;
static float weight_val;
// ------------------------------------------------------- ADDITIONAL FUNCTIONS
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( void )
{
log_cfg_t log_cfg;
loadcell_cfg_t cfg;
/**
* Logger initialization.
* Default baud rate: 115200
* Default log level: LOG_LEVEL_DEBUG
* @note If USB_UART_RX and USB_UART_TX
* are defined as HAL_PIN_NC, you will
* need to define them manually for log to work.
* See @b LOG_MAP_USB_UART macro definition for detailed explanation.
*/
LOG_MAP_USB_UART( log_cfg );
log_init( &logger, &log_cfg );
log_info( &logger, "---- Application Init ----" );
// Click initialization.
loadcell_cfg_setup( &cfg );
LOADCELL_MAP_MIKROBUS( cfg, MIKROBUS_1 );
loadcell_init( &loadcell, &cfg );
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Load cell click \r\n");
log_printf(&logger, "-------------------------\r\n");
Delay_ms( 100 );
loadcell_set_mode( &loadcell, LOADCELL_POWER_UP );
Delay_ms( 100 );
loadcell_reset( &loadcell );
Delay_ms( 100 );
loadcell_set_rate( &loadcell, LOADCELL_10HZ_INTERNAL_OSC );
Delay_ms( 100 );
log_printf(&logger, " Tare the scale : Channel B, Gate 32 \r\n");
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " In the following 10 seconds please REMOVE all object from the scale.\r\n");
Delay_ms( 10000 );
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Start tare scales \r\n");
loadcell_tare ( &loadcell, LOADCELL_CHANN_B_GATE_32_NEXT, &cell_data );
Delay_ms( 500 );
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Tarring completed \r\n");
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " In the following 10 seconds place 100g weight etalon on the scale for calibration purpose.\r\n");
Delay_ms( 10000 );
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Start calibration \r\n");
if ( loadcell_calibration ( &loadcell, LOADCELL_CHANN_B_GATE_32_NEXT, LOADCELL_WEIGHT_100G, &cell_data ) == LOADCELL_GET_RESULT_OK )
{
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Calibration Done \r\n");
log_printf(&logger, "- - - - - - - - - - - - -\r\n");
log_printf(&logger, " In the following 10 seconds please REMOVE all object from the scale.\r\n");
Delay_ms( 10000 );
}
else
{
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Calibration Error \r\n");
for ( ; ; );
}
log_printf(&logger, "-------------------------\r\n");
log_printf(&logger, " Start measurements : \r\n");
log_printf(&logger, "-------------------------\r\n");
}
void application_task ( void )
{
weight_val = loadcell_get_weight( &loadcell, LOADCELL_CHANN_B_GATE_32_NEXT, &cell_data );
log_printf(&logger, " Weight : %.2f\r\n", weight_val );
Delay_ms( 1000 );
}
void main ( void )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
