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?

[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.

[GrantW]

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

[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:

[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]

The following code works. Make sure that the buffer (and returned value) are defined uint32_t. The line "buffer ^= 0x800000;" is essential to avoid the huge #'s starting with 8.

uint32_t CB_SPI_Receive (void) {

uint32_t buffer = 0U;

int i, j, k = 1;

// wait for SDATA to go lo

while (HAL_GPIO_ReadPin (SDATA_GPIO_Port, SDATA_Pin)) ;

// wait 300 ns

for (j = 0; j < 5; j++) k += 19;

// 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);

}

// generate one or 3 more clock pulse to set gain for next sample and set bit 23 before returning

buffer ^= 0x800000;

// for (i = 0; i < 2; i++) {

HAL_GPIO_WritePin (SCLK_GPIO_Port, SCLK_Pin, GPIO_PIN_SET);

HAL_GPIO_WritePin (SCLK_GPIO_Port, SCLK_Pin, GPIO_PIN_RESET);

// }

return buffer;

}

[GrantW]

See my response on the discussion thread.

[GrantW]

See my response on the discussion thread. Good luck!

[Attila_S]

Gonna check it out for sure, cheers mate ☺�?​