PID Closed-Loop Control Experiment Based on STM32F1 Series: Potentiometer Knob Drive

We use ADC2 to implement the potentiometer knob.

Potentiometer Knob Initialization Code.c

void PotentiometerKnob_Init(void){
	/* Enable clock */
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC2, ENABLE);  // Enable ADC2 clock
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);  // Enable GPIOA clock
	/* Set ADC clock */
	RCC_ADCCLKConfig(RCC_PCLK2_Div6);  // Select clock division 6, ADCCLK = 72MHz / 6 = 12MHz
	/* GPIO initialization */
	GPIO_InitTypeDef GPIO_InitStructure;
	GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
	GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_3 | GPIO_Pin_4 | GPIO_Pin_5;
	GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init(GPIOA, &GPIO_InitStructure);  // Initialize PA2, PA3, PA4, PA5 as analog input
	/* ADC initialization */
	ADC_InitTypeDef ADC_InitStructure;  // Define structure variable
	ADC_InitStructure.ADC_Mode = ADC_Mode_Independent;  // Mode, select independent mode, using ADC2 alone
	ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;  // Data alignment, select right alignment
	ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None;  // External trigger, use software trigger, no external trigger
	ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;  // Continuous conversion, disabled, stop after one conversion
	ADC_InitStructure.ADC_ScanConvMode = DISABLE;  // Scan mode, disabled, only convert sequence 1
	ADC_InitStructure.ADC_NbrOfChannel = 1;  // Number of channels, 1, only needs to specify more than 1 in scan mode
	ADC_Init(ADC2, &ADC_InitStructure);  // Pass structure variable to ADC_Init, configure ADC2
	/* Enable ADC */
	ADC_Cmd(ADC2, ENABLE);  // Enable ADC2, ADC starts running
	/* ADC calibration */
	ADC_ResetCalibration(ADC2);  // Fixed process, internal circuit will automatically execute calibration
	while (ADC_GetResetCalibrationStatus(ADC2) == SET);
	ADC_StartCalibration(ADC2);
	while (ADC_GetCalibrationStatus(ADC2) == SET);
}

Overall Function Purpose

Open the clock for ADC2 and GPIOA;
Configure ADC2 clock to 12 MHz;
Configure GPIOA’s PA2, PA3, PA4, PA5 as analog input (ADC input pins);
Configure ADC2 parameters (operating mode, alignment, trigger mode, etc.);
Enable ADC2 and complete calibration.

Code Breakdown

1. Enable Clock

RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC2, ENABLE);  // Enable ADC2 clock
RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);  // Enable GPIOA clock

Reason: In STM32, peripherals must have their clocks enabled before use, otherwise the registers will not work.
Here, the clocks for ADC2 and GPIOA are enabled.

2. Set ADC Clock

RCC_ADCCLKConfig(RCC_PCLK2_Div6);  // ADC clock = 72 MHz / 6 = 12 MHz

The ADC clock in STM32 comes from the APB2 bus (PCLK2).
APB2 = 72 MHz, so dividing by 6 gives 12 MHz.
The maximum ADC clock for STM32F1 series cannot exceed 14 MHz.

3. GPIO Initialization (Analog Input)

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN;
GPIO_InitStructure.GPIO_Pin = GPIO_Pin_2 | GPIO_Pin_3 | GPIO_Pin_4 | GPIO_Pin_5;
GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
GPIO_Init(GPIOA, &GPIO_InitStructure);

Configure PA2, PA3, PA4, PA5 as analog input.
GPIO_Mode_AIN = analog input, indicating these pins are directly connected to the ADC, bypassing digital circuits.
GPIO_Speed has no effect in analog mode but must be specified.

4. ADC Parameter Initialization

ADC_InitStructure.ADC_Mode = ADC_Mode_Independent;
ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right;
ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None;
ADC_InitStructure.ADC_ContinuousConvMode = DISABLE;
ADC_InitStructure.ADC_ScanConvMode = DISABLE;
ADC_InitStructure.ADC_NbrOfChannel = 1;
ADC_Init(ADC2, &ADC_InitStructure);

Independent Mode (ADC_Mode_Independent) STM32 has ADC1, ADC2 (some models also have ADC3), which can sample in dual mode; here only ADC2 is used, selecting independent mode.
Data Alignment (ADC_DataAlign_Right) The ADC result is 12 bits, right alignment means the lower 12 bits are valid, and the upper 4 bits are filled with 0.
Trigger Mode (ADC_ExternalTrigConv_None) No external trigger is used; it is started by software.
Continuous Conversion Mode (ADC_ContinuousConvMode) Disabled, meaning only one sample is taken, then it stops.
Scan Mode (ADC_ScanConvMode) Disabled, meaning only one channel is sampled. If multiple channels need to be sampled sequentially, scan mode must be enabled, and ADC_NbrOfChannel > 1 must be set.
Number of Channels (ADC_NbrOfChannel = 1) Only one channel is configured, corresponding to non-scan mode.

5. Enable ADC

ADC_Cmd(ADC2, ENABLE);

Enable ADC2 to allow it to operate.

6. ADC Calibration

ADC_ResetCalibration(ADC2);  // Reset calibration register
while (ADC_GetResetCalibrationStatus(ADC2) == SET);
ADC_StartCalibration(ADC2);  // Start calibration
while (ADC_GetCalibrationStatus(ADC2) == SET);

Why calibrate? The ADC has analog circuits that may deviate due to temperature and power supply. STM32 provides an internal calibration function that automatically adjusts the offset to improve accuracy.
Fixed process:

Reset the calibration register first;
Wait for the reset to complete;
Start calibration;
Wait for calibration to complete.

Please refer to the ADC Basics Study

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Get the AD value function of the potentiometer knob.c

* Parameter: n specifies the potentiometer knob, range: 1~4, representing RP1, RP2, RP3, RP4 respectively

* Return value: AD conversion value, range: 0~4095

uint16_t RP_GetValue(uint8_t n){
	if (n == 1)  // Specify to read RP1
	{
		/* Configure the regular group for channel 2 (PA2) */
		ADC_RegularChannelConfig(ADC2, ADC_Channel_2, 1, ADC_SampleTime_55Cycles5);
	}
	else if (n == 2)  // Specify to read RP2
	{
		/* Configure the regular group for channel 3 (PA3) */
		ADC_RegularChannelConfig(ADC2, ADC_Channel_3, 1, ADC_SampleTime_55Cycles5);
	}
	else if (n == 3)  // Specify to read RP3
	{
		/* Configure the regular group for channel 4 (PA4) */
		ADC_RegularChannelConfig(ADC2, ADC_Channel_4, 1, ADC_SampleTime_55Cycles5);
	}
	else if (n == 4)  // Specify to read RP4
	{
		/* Configure the regular group for channel 5 (PA5) */
		ADC_RegularChannelConfig(ADC2, ADC_Channel_5, 1, ADC_SampleTime_55Cycles5);
	}
	ADC_SoftwareStartConvCmd(ADC2, ENABLE);  // Software trigger AD conversion once
	while (ADC_GetFlagStatus(ADC2, ADC_FLAG_EOC) == RESET);  // Wait for EOC flag, i.e., wait for AD conversion to complete
	return ADC_GetConversionValue(ADC2);  // Read data register to get AD conversion result
}

Function Purpose

uint16_t RP_GetValue(uint8_t n)

Input parameter n: indicates which channel to read (1~4).
Return value: returns the ADC conversion result (range 0~4095, 12-bit ADC).

2. Select Channel

if (n == 1) // Read RP1
{
	ADC_RegularChannelConfig(ADC2, ADC_Channel_2, 1, ADC_SampleTime_55Cycles5);
}
else if (n == 2) // Read RP2
{
	ADC_RegularChannelConfig(ADC2, ADC_Channel_3, 1, ADC_SampleTime_55Cycles5);
}
else if (n == 3) // Read RP3
{
	ADC_RegularChannelConfig(ADC2, ADC_Channel_4, 1, ADC_SampleTime_55Cycles5);
}
else if (n == 4) // Read RP4
{
	ADC_RegularChannelConfig(ADC2, ADC_Channel_5, 1, ADC_SampleTime_55Cycles5);
}

Here, the function is used:

ADC_RegularChannelConfig(ADC_TypeDef* ADCx, uint8_t ADC_Channel, uint8_t Rank, uint8_t SampleTime);

Parameter description:

ADC2: Select ADC2.
ADC_Channel_x: Specify ADC channel (PA2=Channel_2, PA3=Channel_3, PA4=Channel_4, PA5=Channel_5).
Rank=1: Specify as the first in the regular sequence (since scan mode is not enabled, there is only one).
SampleTime=55Cycles5: Sample time, indicating that the ADC holds the sample for 55.5 cycles.

3. Software Trigger One Conversion

ADC_SoftwareStartConvCmd(ADC2, ENABLE);

Start one regular group conversion (software trigger mode).
Since it was configured during initialization as ADC_ExternalTrigConv = None, it must be started by software.

4. Wait for Conversion to Complete

while (ADC_GetFlagStatus(ADC2, ADC_FLAG_EOC) == RESET);

EOC = End Of Conversion (conversion complete flag).
The code will block here until the conversion is complete.

5. Read Result

return ADC_GetConversionValue(ADC2);

Return the converted digital value (0~4095).
Relationship between digital value and voltage:

Where Vref is typically 3.3V.

For example: If the sampling result = 2048, it indicates the input voltage is approximately: