read input value from external device STM32F107 - c

Question

I am new to the processor STM32F107. I have to read the input value from an external source that is a balance. This balance is external to the board that contains the processor and communicates with it via PA4.
What I have to do to read the analogue input from the balance?
Here is my first attempt to read the input from the balance.
I use this function to setup the ADC:
void ADC_Configuration(void) {
ADC_InitTypeDef ADC_InitStructure;
/* PCLK2 is the APB2 clock */
/* ADCCLK = PCLK2/6 = 72/6 = 12MHz*/
RCC_ADCCLKConfig(RCC_PCLK2_Div6);
/* Enable ADC1 clock so that we can talk to it */
RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC1, ENABLE);
/* Put everything back to power-on defaults */
ADC_DeInit(ADC1);
/* ADC1 Configuration ------------------------------------------------------*/
/* ADC1 and ADC2 operate independently */
ADC_InitStructure.ADC_Mode = ADC_Mode_Independent;
/* Disable the scan conversion so we do one at a time */
ADC_InitStructure.ADC_ScanConvMode = DISABLE;
/* Don't do contimuous conversions - do them on demand */
ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;
/* Start conversin by software, not an external trigger */
ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None;
/* Conversions are 12 bit - put them in the lower 12 bits of the result */
ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
/* Say how many channels would be used by the sequencer */
ADC_InitStructure.ADC_NbrOfChannel = 1;
/* Now do the setup */ ADC_Init(ADC1, &ADC_InitStructure);
/* Enable ADC1 */ ADC_Cmd(ADC1, ENABLE);
/* Enable ADC1 reset calibaration register */
ADC_ResetCalibration(ADC1);
/* Check the end of ADC1 reset calibration register */
while(ADC_GetResetCalibrationStatus(ADC1));
/* Start ADC1 calibaration */
ADC_StartCalibration(ADC1);
/* Check the end of ADC1 calibration */
while(ADC_GetCalibrationStatus(ADC1));
}
And I use this function to get the input:
u16 readADC1(u8 channel) {
ADC_RegularChannelConfig(ADC1, channel, 1, ADC_SampleTime_1Cycles5);
// Start the conversion
ADC_SoftwareStartConvCmd(ADC1, ENABLE);
// Wait until conversion completion
while(ADC_GetFlagStatus(ADC1, ADC_FLAG_EOC) == RESET);
// Get the conversion value
return ADC_GetConversionValue(ADC1);
}
The problem is that in N measurements of the same weight, I get N different results.
For example, the weight is 70kg and the output of the readADC1(ADC_Channel_4) is 715,760,748,711,759 etc.
What am I doing wrong?

Answer 1

The balance has a load cell inside it, which generates an analog voltage. The processor on the balance is some how not utilized (i assume this as not much details are present in your question).
The stm32 f107 controller has an on-chip ADC (analog to digital convertor). Connect the output of load cell (analog signal coming from balance) to the analog input pin of stm32 f107. Configure the ADC to sample and convert the analog signal into digital (use the example code as reference to write the software).

Answer 2

PA4 is multiplexed with ADC12_IN4 (an analogue input that can itself be mapped to channel 4 on either ADC1 or ADC2).
Programming the ADC, selecting the correct peripheral clocking and mapping multiplexed pins on STM32 is somewhat complex, but I strongly suggest that you utilise the STM32F10x Standard Peripheral Library which provides an API for all STM32F10x peripherals as well as numerous examples of how to use the library, including ADC examples.
The ADC itself may be polled, interrupt driven, use DMA, and be software triggered or free-running, self-clocked or clocked from a timer peripheral. The options are numerous, only some combinations are covered by the example code, but it is a good place to start nonetheless. To understand all the options and how to use them with the Standard Peripheral Library, you will need a fairly thorough understanding of the Reference Manual.
Another resource you may find useful is STM's MicroXplorer. This allows visual configuration and allocation of multiplexed pins and generates source code you can use directly.
Furthermore you may need some hardware signal conditioning at the input to ensure that the input is within the valid and tolerable range of the ADC input.