trying to interface with an HX711 load cell amp

[GrantW]

The HX711 requires the MCU to send an exact number of clock pulses to capture a 24 bit value, then the clock signal must remain low until the HX711 indicates its ready to transmit again, using the data line. I tried to use a GPIO pin to generate the clock signal manually with pin_set and pin_reset calls, which works in that it creates a clock signal at the frequency of the APB, but the amplitude is only 100 mv. When I plug the clock signal into the HX711 the signal becomes low level noise. Here is the pin config:

 /*Configure GPIO pin : SCLK_Pin */
 GPIO_InitStruct.Pin = SCLK_Pin;
 GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
 GPIO_InitStruct.Pull = GPIO_PULLUP;
 GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
 HAL_GPIO_Init(SCLK_GPIO_Port, &GPIO_InitStruct);

and here is the clock gen code:

	// read 24 data bits
	for (i = 0; i < 24; i++) {
	 HAL_GPIO_WritePin (SCLK_GPIO_Port, SCLK_Pin, GPIO_PIN_SET);
	 buffer <<= 1;
	 HAL_GPIO_WritePin (SCLK_GPIO_Port, SCLK_Pin, GPIO_PIN_RESET);
	 buffer += HAL_GPIO_ReadPin (SDATA_GPIO_Port, SDATA_Pin);
	}

I should be getting a 3.3V clock signal. Any suggestions?

[Uwe Bonnes]

Read the datasheet carefully again. You need at least 25 bit cycles. And when, for example, some interrupt prolongs your SCK high for longer than 50 us, you get a reset. So you better read with interrupts disabled. With 26 or 27 bit you select the other channel ot another gain.

[GrantW]

Uwe, thats good information but doesn't address the problem: a weak clock signal. My code snippet is not the whole app, just the parts that deal with this issue.

[Uwe Bonnes]

What SCK frequency do you get with above code? How is the HX711 connected? Maybe GPIO_SPEED_FREQ_LOW will result in the setup above in a "weak clock signal"?

[Ozone]

Do you have the clock to the "SCLK_Port" enabled ?

SCLK_Port is just a define for a "real" port like A, B, ...

Anything other connected to that pin ?

This is a common issue with ST's Discovery board.

> ... , then the clock signal must remain low until the HX711 indicates its ready to transmit again ...

This suggests you want a pull-down resistor, rather then the pull-up you configured.

An external pull-down would be better, as it works even with unconfigured GPIOs, avoiding troublesome transitional signals during startup.

[GrantW]

I tried another pin and am now getting a nice 3.3v signal. For reference, I am using the Nucleo F413 (aka Nucleo 144). The pin that gave me trouble was PE2. Pin PA6 works. As I mentioned in my initial question, the clock speed is the speed of the APB that the port is driven by. Thanks for your suggestions.

[Attila_S]

Hey!

​

I am a newby, but i am i a school project where i have to do a scale.

I set up the hx711 and the load cell with my nucleo card, but the card does not se

d clock signal to the hx711.

I am using a hx711 library i found at:

github.com/freakone/HX711

​

Could you please help me?!:folded_hands:

​

Thanks in advance.​

​

[GrantW]

Can u show your code and how u configured the clock & data pins?

[Attila_S]

Of course,

I use CubeMX to configurate the pins as u can see in the first picture.

And here is my code:

1. main
2. hx711.c
3. hx711.h

/* USER CODE BEGIN Header */
/**
 ******************************************************************************
 * @file : main.c
 * @brief : Main program body
 ******************************************************************************
 * @attention
 *
 * <h2><center>&copy; Copyright (c) 2019 STMicroelectronics.
 * All rights reserved.</center></h2>
 *
 * This software component is licensed by ST under BSD 3-Clause license,
 * the "License"; You may not use this file except in compliance with the
 * License. You may obtain a copy of the License at:
 * opensource.org/licenses/BSD-3-Clause
 *
 ******************************************************************************
 */
/* USER CODE END Header */
 
/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "dma.h"
#include "usart.h"
#include "gpio.h"
 
/* Private includes ----------------------------------------------------------*/
/* USER CODE BEGIN Includes */
#include "hx711.h"
#include "string.h"
/* USER CODE END Includes */
 
/* Private typedef -----------------------------------------------------------*/
/* USER CODE BEGIN PTD */
 
/* USER CODE END PTD */
 
/* Private define ------------------------------------------------------------*/
/* USER CODE BEGIN PD */
 
/* USER CODE END PD */
 
/* Private macro -------------------------------------------------------------*/
/* USER CODE BEGIN PM */
 
/* USER CODE END PM */
 
/* Private variables ---------------------------------------------------------*/
 
/* USER CODE BEGIN PV */
volatile int meres =0;
volatile int meresAtlag =0;
/* USER CODE END PV */
 
/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
/* USER CODE BEGIN PFP */
 
/* USER CODE END PFP */
 
/* Private user code ---------------------------------------------------------*/
/* USER CODE BEGIN 0 */
 
/* USER CODE END 0 */
 
/**
 * @brief The application entry point.
 * @retval int
 */
int main(void)
{
 /* USER CODE BEGIN 1 */
 HX711 hx11;
 hx11.gpioSck = HS711SCK_GPIO_Port;
 hx11.gpioData = HX711OUTPUT_GPIO_Port;
 hx11.pinSck = HS711SCK_Pin;
 hx11.pinData = HX711OUTPUT_Pin;
 hx11.offset = 0;
 hx11.gain = 64;
 
 /* USER CODE END 1 */
 
 
 /* MCU Configuration--------------------------------------------------------*/
 
 /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
 HAL_Init();
 
 /* USER CODE BEGIN Init */
 
 /* USER CODE END Init */
 
 /* Configure the system clock */
 SystemClock_Config();
 
 /* USER CODE BEGIN SysInit */
 
 /* USER CODE END SysInit */
 
 /* Initialize all configured peripherals */
 MX_GPIO_Init();
 MX_USART2_UART_Init();
 MX_DMA_Init();
 /* USER CODE BEGIN 2 */
 HX711_Init(hx11);
 
uint8_t masage[100];
//uint8_t times = 4;
 
//uint8_t times = 4;
//meresAtlag = HX711_AverageValue(hx11, times);
 /* USER CODE END 2 */
 
 /* Infinite loop */
 /* USER CODE BEGIN WHILE */
 while (1)
 {
	 meres = HX711_Value(hx11);
	 //meres = HX711_AverageValue(hx11, times);
	 HAL_Delay(500);
	 HAL_UART_Transmit(&huart2, masage, sprintf(masage,"%d\n\r", meres),1000);
 /* USER CODE END WHILE */
 
 /* USER CODE BEGIN 3 */
 }
 /* USER CODE END 3 */
}
 
/**
 * @brief System Clock Configuration
 * @retval None
 */
void SystemClock_Config(void)
{
 RCC_OscInitTypeDef RCC_OscInitStruct = {0};
 RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
 
 /** Initializes the CPU, AHB and APB busses clocks 
 */
 RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSI;
 RCC_OscInitStruct.HSIState = RCC_HSI_ON;
 RCC_OscInitStruct.HSICalibrationValue = RCC_HSICALIBRATION_DEFAULT;
 RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
 RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSI_DIV2;
 RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL16;
 if (HAL_RCC_OscConfig(&RCC_OscInitStruct) != HAL_OK)
 {
 Error_Handler();
 }
 /** Initializes the CPU, AHB and APB busses clocks 
 */
 RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_HCLK|RCC_CLOCKTYPE_SYSCLK
 |RCC_CLOCKTYPE_PCLK1|RCC_CLOCKTYPE_PCLK2;
 RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
 RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1;
 RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2;
 RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1;
 
 if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2) != HAL_OK)
 {
 Error_Handler();
 }
}
 
/* USER CODE BEGIN 4 */
 
/* USER CODE END 4 */
 
/**
 * @brief This function is executed in case of error occurrence.
 * @retval None
 */
void Error_Handler(void)
{
 /* USER CODE BEGIN Error_Handler_Debug */
 /* User can add his own implementation to report the HAL error return state */
 
 /* USER CODE END Error_Handler_Debug */
}
 
#ifdef USE_FULL_ASSERT
/**
 * @brief Reports the name of the source file and the source line number
 * where the assert_param error has occurred.
 * @param file: pointer to the source file name
 * @param line: assert_param error line source number
 * @retval None
 */
void assert_failed(uint8_t *file, uint32_t line)
{ 
 /* USER CODE BEGIN 6 */
 /* User can add his own implementation to report the file name and line number,
 tex: printf("Wrong parameters value: file %s on line %d\r\n", file, line) */
 /* USER CODE END 6 */
}
#endif /* USE_FULL_ASSERT */
 
/************************ (C) COPYRIGHT STMicroelectronics *****END OF FILE****/

#include "hx711.h"
 
void HX711_Init(HX711 data)
{
//	GPIO_InitTypeDef GPIO_InitStruct;
//	GPIO_InitStruct.Pin = data.pinSck;
//	GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
//	GPIO_InitStruct.Pull = GPIO_NOPULL;
//	GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
//	HAL_GPIO_Init(data.gpioSck, &GPIO_InitStruct);
//
//	GPIO_InitStruct.Pin = data.pinData;
//	GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
//	GPIO_InitStruct.Pull = GPIO_PULLUP;
//	GPIO_InitStruct.Speed = GPIO_SPEED_FREQ_LOW;
//	HAL_GPIO_Init(data.gpioData, &GPIO_InitStruct);
 
	HAL_GPIO_WritePin(data.gpioSck, data.pinSck, GPIO_PIN_SET);
	HAL_Delay(50);
	HAL_GPIO_WritePin(data.gpioData, data.pinSck, GPIO_PIN_RESET);
 
}
 
int HX711_Average_Value(HX711 data, uint8_t times)
{
 int sum = 0;
 for (int i = 0; i < times; i++)
 {
 sum += HX711_Value(data);
 }
 
 return sum / times;
}
 
int HX711_Value(HX711 data)
{
 int buffer;
 buffer = 0;
 
 while (HAL_GPIO_ReadPin(data.gpioData, data.pinData)==1)
 ;
 
 for (uint8_t i = 0; i < 24; i++)
 {
 	HAL_GPIO_WritePin(data.gpioSck, data.pinSck, GPIO_PIN_SET);
 
 buffer = buffer << 1 ;
 
 if (HAL_GPIO_ReadPin(data.gpioData, data.pinData))
 {
 buffer ++;
 }
 
 HAL_GPIO_WritePin(data.gpioSck, data.pinSck, GPIO_PIN_RESET);
 }
 
 for (int i = 0; i < data.gain; i++)
 {
 	HAL_GPIO_WritePin(data.gpioSck, data.pinSck, GPIO_PIN_SET);
 	HAL_GPIO_WritePin(data.gpioSck, data.pinSck, GPIO_PIN_RESET);
 }
 
 buffer = buffer ^ 0x800000;
 
 return buffer;
}
 
HX711 HX711_Tare(HX711 data, uint8_t times)
{
 int sum = HX711_Average_Value(data, times);
 data.offset = sum;
 return data;
}
 

#ifndef HX711_H_
#define HX711_H_
 
//#include "stm32f3xx_hal.h"
#include "main.h"
 
typedef struct _hx711
{
	GPIO_TypeDef* gpioSck;
	GPIO_TypeDef* gpioData;
	uint16_t pinSck;
	uint16_t pinData;
	int offset;
	int gain;
	// 1: channel A, gain factor 128
	// 2: channel B, gain factor 32
 // 3: channel A, gain factor 64
} HX711;
 
 
void HX711_Init(HX711 data);
HX711 HX711_Tare(HX711 data, uint8_t times);
int HX711_Value(HX711 data);
int HX711_AverageValue(HX711 data, uint8_t times);
 
#endif /* HX711_H_ */

And it retuns 8388608 in the meres variable.

:(

Thanks for helping me!

[GrantW]

It may be working. The clock signals are generated in HX711_Value() by toggling the clock pin. Its a peculiar protocol. The rate is limited by the speed of the clock controlling that pin (APB1 or APB2). This must be less than 5 MHz for the load cell to keep up. Did you try pressing on the load cell to see it the number changes?

[GrantW]

I just re-read your question and saw that the amplitude is too low. Try using another pin (I had the same problem). On an stmf413 pins PA5, PA6 or PA7 work well.

[Attila_S]

Hi again!

I added some function to my code so now I am getting the clock signal:

void power_down() {
	HAL_GPIO_WritePin(HS711SCK_GPIO_Port, HS711SCK_Pin, 0);
	HAL_GPIO_WritePin(HS711SCK_GPIO_Port, HS711SCK_Pin, 1);
}
 
void power_up() {
	HAL_GPIO_WritePin(HS711SCK_GPIO_Port, HS711SCK_Pin, 0);
}

I use it like that:

while (1)
 {
	 power_up();
	 meres =HX711_Average_Value(hx11, 1);
			 //HX711_Value(hx11);
	 meres = meres-offs;
	 HAL_Delay(100);
	 power_down();
	 //meres = HX711_AverageValue(hx11, times);
	 HAL_Delay(500);
	 HAL_UART_Transmit(&huart2, masage, sprintf(masage,"%d\n\r", meres),1000);
 /* USER CODE END WHILE */
 
 /* USER CODE BEGIN 3 */
 }

So now I'am finally getting back something else than 8388608 but they are still random numbers for some reason.

Here is my setup:

[GrantW]

ok, got a bit confused there. I was reading MY original question. Ha!

[CüneytKüçük]

Hİ Atilla_S, Did you solve the problem? "8388608" value is seen when I follow the same steps.

[Attila_S]

Hi same thing here, working on it :persevering_face:​

[GrantW]

See my response on the discussion thread. Good luck!