CODEWITHSUNDEEP
cstm32data-conversionadc
coollime
coollime

Reputation: 147

How to convert reading ADC Value to Float?

I want to convert ADC Values to float numbers. This is my code:

uint32_t ADCValue;
char str[15];

          ADCValue = HAL_ADC_GetValue(&hadc1);
          ADCValue=ADCValue*3.3/4095;
          sprintf(str, "%d", Voltage);
          HAL_UART_Transmit(&huart2, (uint8_t*)(&str), 6, 100);
          HAL_UART_Transmit(&huart2, (uint8_t*) "\n\r", 2, 100);
          HAL_Delay(500);

I am reading value of 4095 at 3.3V but I am transmitting 3 to buffer. I want to transmit exact value of voltage.

Upvotes: 3

Views: 8354

Answers (4)

chux
chux

Reputation: 153517

In addition to other fine answers, consider:

Integer division truncates the factional part of the mathematical quotient.

Instead, perform a rounded integer division. With unsigned integer math, add half the divisor before the division.

// ADCValue=ADCValue*3.3/4095;

unsigned Voltage = // millivolts
Voltage = (ADCValue*3300 + 4095/2)/4095.

Upvotes: 0

Lundin
Lundin

Reputation: 213920

There is no apparent reason why you need to use float numbers here in the first place. They are needlessly slow. Simply do this:

uint32_t millivolts = ADCValue*3300/4095.

For an input of 4095, you get the result 3299mV. This is possibly more accurate than what you would get through float numbers, because of floating-point inaccuracy.

Upvotes: 6

Jabberwocky
Jabberwocky

Reputation: 50802

You probably want this:

ADCValue = HAL_ADC_GetValue(&hadc1);
float fADCValue = (float)ADCValue*3.3 / 4095.0;
int txlength = sprintf(str, "%.2f", fADCValue);
HAL_UART_Transmit(&huart2, (uint8_t*)(&str), txlength, 100);
HAL_UART_Transmit(&huart2, (uint8_t*) "\n\r", 2, 100);
HAL_Delay(500);

Caution: this only works if the float type is available on your platform.

If floating point is not available you can use this:

ADCValue = HAL_ADC_GetValue(&hadc1);
ADCValue = ADCValue * 330 / 4095;
int len = sprintf(str, "%d.%02d", ADCValue / 100, ADCValue % 100);
HAL_UART_Transmit(&huart2, (uint8_t*)(&str), leb, 100);
HAL_UART_Transmit(&huart2, (uint8_t*) "\n\r", 2, 100);

This is a quick hack and there is certainly room for improvement.

Demonstration here.

Upvotes: 5

Rishikesh Raje
Rishikesh Raje

Reputation: 8614

This should do the trick

float Adcvalue_f;
uint32_t ADCValue;
char str[15];
....
ADCValue = HAL_ADC_GetValue(&hadc1); 
ADCValue_f =ADCValue*3.3/4095;
sprintf(str, "%2.2f", AdcValue_f);   //Adjust the .2 as per required precision
HAL_UART_Transmit(&huart2, (uint8_t*)(&str), 6, 100);
HAL_UART_Transmit(&huart2, (uint8_t*) "\n\r", 2, 100);

Upvotes: 0

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