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01.Battery voltage detection (ADC)

Battery voltage detection (ADC)

Battery voltage detection (ADC)Hardware connectionControl PrinciplePin definitionSoftware codeControl functionExperimental phenomenon

The tutorial demonstrates the low voltage alarm function of the development board.


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ADC collects the actual voltage of the battery pack, and determines whether to issue an alarm and the LED status through the obtained voltage value!

The tutorial only introduces the standard library project code

Hardware connection

Peripherals	Development Board	Description
Battery Pack	PA5	The battery pack DC interface needs to be connected to the development board

Control Principle

The converted value of the battery BAT pin is obtained through a single ADC.

ADC

STM32F103RCT6 has three 12-bit analog-to-digital converters embedded, and each ADC controller has up to 16 channels.

ADC Channel

Only introduce the ADC channel corresponding to the battery pack interface.

Main control chip	Pin	Main function (after reset)	Default multiplexing function	Redefine function
STM32F103RCT6	PA5	PA5	SPI1_SCK/DAC_OUT2/ADC12_IN5

ADC conversion value

The ADC of STM32F103RCT6 is a 12-bit successive approximation analog-to-digital converter with 12-bit resolution;

A D C v a l u e r a n g e = 0 - 2^{12} = 0 - 4095

The converted value of ADC can be stored in 16-bit data register in left-aligned or right-aligned mode.

ADC conversion mode

The A/D conversion of each ADC channel can be performed in single, continuous, scan or intermittent mode.

Mode	Function
Single conversion mode	ADC performs only one conversion
Continuous conversion mode	Starts another conversion as soon as the previous ADC conversion is completed
Scan mode	Used to scan a group of ADC channels
Intermittent mode	Converts multiple ADC channels in groups until the entire sequence is converted


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Regular channel: Perform channel conversion in a certain order
Injection channel: The injection channel can interrupt the conversion of the regular channel to execute the injection channel, and then continue to execute the regular channel conversion after the injection channel is completed

ADC conversion time

The input clock of the ADC must not exceed 14MHz, which is generated by the frequency division of PCLK2.

T o t a l c o n v e r s i o n t i m e = T_{C O N V} = s a m p l i n g t i m e + 12.5 c l o c k c y c l e s

Conversion time in this tutorial: ADC clock frequency 12MHz, sampling time 239.5 clock cycles

T o t a l c o n v e r s i o n t i m e = T_{C O N V} = s a m p l i n g t i m e + 12.5 c l o c k c y c l e s = (239.5 + 12.5) * \frac{1}{12000000} = 21 u s

Actual voltage conversion: ADC internal reference voltage 3.3V

V_{B A T} = \frac{V a l u e_{A D C c o n v e r t e d v a l u e} * （ 3.3 ）}{4096}

Referring to the hardware schematic diagram, we can see: Current equality principle

I_{c u r r e n t} = \frac{V_{B A T}}{R 16} = \frac{V_{M}}{R 16 + R 14} ⟹ \frac{V_{B A T}}{3.3} = \frac{V_{M}}{10 + 3.3} ⟹ V_{M} = \frac{V_{B A T} * （ 10 + 3.3 ）}{3.3}

T h a t i s, t h e a c t u a l v o l t a g e = V_{M} = \frac{V_{B A T} * （ 10 + 3.3 ）}{3.3}

Pin definition

Main control chip	Pin	Main function (after reset)	Default multiplexing function	Redefine function
STM32F103RCT6	PA5	PA5	SPI1_SCK/DAC_OUT2/ADC12_IN5

Software code

Since the default function of the PA5 pin is a normal IO pin function, we need to use the multiplexing function.


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Product supporting data source code path: Attachment → Source code summary → 2.Extended_Course → 1.Battery

Control function

The tutorial only briefly introduces the code, you can open the project source code to read it.

Battery_init


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//Battery power detection initialization
void Battery_init(void)
{
    ADC_InitTypeDef ADC_InitStructure;
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(BAT_GPIO_CLK | BAT_ADC_CLK, ENABLE); //Enable BAT_ADC channel clock
    RCC_ADCCLKConfig(RCC_PCLK2_Div6); //Set ADC division factor 6

    //72M/6=12, ADC maximum input clock cannot exceed 14M
    //PA5 as analog channel input pin
    GPIO_InitStructure.GPIO_Pin = BAT_GPIO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AIN; //Analog input
    GPIO_Init(BAT_GPIO_PORT, &GPIO_InitStructure); //Initialize GPIOA.5

    ADC_DeInit(BAT_ADC); //Reset BAT_ADC and reset all registers of the peripheral BAT_ADC to default values
    ADC_InitStructure.ADC_Mode = ADC_Mode_Independent; //ADC independent mode
    ADC_InitStructure.ADC_ScanConvMode = DISABLE; //Single channel mode
    ADC_InitStructure.ADC_ContinuousConvMode = DISABLE; //Single conversion mode
    ADC_InitStructure.ADC_ExternalTrigConv = ADC_ExternalTrigConv_None; //Conversion is started by software instead of external trigger
    ADC_InitStructure.ADC_DataAlign = ADC_DataAlign_Right; //ADC data right alignment
    ADC_InitStructure.ADC_NbrOfChannel = 1; //Number of ADC channels for regular conversion in sequence
    ADC_Init(BAT_ADC, &ADC_InitStructure); //Initialize peripheral ADCx according to specified parameters
    ADC_Cmd(BAT_ADC, ENABLE); //Enable specified BAT_ADC
    ADC_ResetCalibration(BAT_ADC); //Start reset calibration
    while (ADC_GetResetCalibrationStatus(BAT_ADC)); //Wait for reset calibration to end
    ADC_StartCalibration(BAT_ADC); //Start AD calibration
    while (ADC_GetCalibrationStatus(BAT_ADC)); //Wait for calibration to end
}

Battery_Get


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// Get ADC value, ch: channel value
static uint16_t Battery_Get(uint8_t ch)
{
    uint16_t timeout = 1000;
    //Set the regular group channel of the specified ADC, set their conversion order and sampling time
    ADC_RegularChannelConfig(BAT_ADC, ch, 1, ADC_SampleTime_239Cycles5);
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