Ultrasonic module-measuring distance (TIM)

Ultrasonic module-measuring distance (TIM)Hardware connectionControl principlePin definitionSoftware codeControl functionExperimental phenomenon

The tutorial mainly demonstrates the implementation of the ultrasonic module distance measurement function.


GPIO general push-pull output function triggers the ultrasonic module distance measurement; timer input capture obtains the ultrasonic high level time, thereby calculating the obstacle distance.
The tutorial only introduces the standard library project code

Hardware connection

Just install it to the corresponding interface:

Ultrasonic module	STM32F103RCT6
VCC	5V
TRIG	PA0
ECHO	PA1
GND	GND

Control principle

Trigger ranging signal

The TRIG pin sends a high level signal for more than 10us.


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The ultrasonic module will automatically send 8 40KHz square waves and automatically detect whether there is a signal return

Receive echo signal

If there is a signal return, the ECHO pin will output a high level. The duration of the high level is the time from the ultrasonic wave transmission to the return.

Distance conversion

D_{i s t a n c e} = \frac{T_{h i g h} * V_{s p e e d}}{2}


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T: Echo signal high level time
V: Sound speed (approximately equal to 340m/s)

Pin definition

Main control chip	Pin	Main function (after reset)	Default multiplexing function	Redefine function
STM32F103RCT6	PA0	PA0	WKUP/USART2_CTS/ADC123_IN0/TIM2_CH1_ETR/TIM5_CH1/TIM8_ETR
STM32F103RCT6	PA1	PA1	USART2_RTS/ADC123_IN1/TIM5_CH2/TIM2_CH2

Software code

Since the default function of all pins is the ordinary IO pin function, we need to use the multiplexing function.


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Product supporting materials source code path: Attachment → Source code summary → 2.Extended_Course → 2.Ultrasonic

Control function

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

ultrasonic_init


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static void ultrasonic_init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    RCC_APB2PeriphClockCmd(ULTRASONIC_RCC, ENABLE);   // Enable the GPIOA clock

    GPIO_InitStructure.GPIO_Pin  = ECHO_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IPD;  //PA1 Input
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;      //50M
    GPIO_Init(ECHO_PORT, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Pin  = TRIG_PIN;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;      //PA3 output
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;      //50M
    GPIO_Init(TRIG_PORT, &GPIO_InitStructure);
}

TIM2_Cap_Init


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void TIM2_Cap_Init(u16 arr,u16 psc) 
{
    TIM_ICInitTypeDef TIM2_ICInitStructure;
    TIM_TimeBaseInitTypeDef TIM_TimeBaseStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    ultrasonic_init();
    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE); //Enable TIM2 clock

    //Initialize timer 2 TIM2
    TIM_TimeBaseStructure.TIM_Period = arr; //Set counter auto-reload value
    TIM_TimeBaseStructure.TIM_Prescaler = psc; //Prescaler
    TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1; //Set clock division: TDTS = Tck_tim
    TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up; //TIM up counting mode
    TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure); //Initialize the time base unit of TIMx according to the parameters specified in TIM_TimeBaseInitStruct

    //Initialize TIM2 input capture parameters
    TIM2_ICInitStructure.TIM_Channel = TIM_Channel_2; //CC1S=02 Select input IC2 to map to TI1
    TIM2_ICInitStructure.TIM_ICPolarity = TIM_ICPolarity_Rising; //Rising edge capture
    TIM2_ICInitStructure.TIM_ICSelection = TIM_ICSelection_DirectTI;
    TIM2_ICInitStructure.TIM_ICPrescaler = TIM_ICPSC_DIV1; //Configure input frequency division, no frequency division
    TIM2_ICInitStructure.TIM_ICFilter = 0x00; //Configure input filter No filtering
    TIM_ICInit(TIM2, &TIM2_ICInitStructure);

    //Interrupt group initialization
    NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn; //TIM2 interrupt
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1; //Preempt priority level 1
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1; //From priority level 1
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE; //IRQ channel is enabled
    NVIC_Init(&NVIC_InitStructure); //Initialize peripheral NVIC registers according to the parameters specified in NVIC_InitStruct
    TIM_ITConfig(TIM2,TIM_IT_Update|TIM_IT_CC2,ENABLE);//Allow update interrupts, allow CC2IE to capture interrupts
    TIM_Cmd(TIM2,ENABLE); //Enable timer 2
}

TIM2_IRQHandler


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void TIM2_IRQHandler(void)
{
    u16 tsr;
    tsr=TIM2->SR;
    if((TIM2CH2_CAPTURE_STA&0X80)==0)// Capture has not succeeded
    {
        if(tsr&0X01)// The timer overflows
        {
            if(TIM2CH2_CAPTURE_STA&0X40)// The high level has been captured
            {
                if((TIM2CH2_CAPTURE_STA&0X3F)==0X3F)// The high level is too long
                {
                    TIM2CH2_CAPTURE_STA|=0X80;       // Indicates a successful capture
                    TIM2CH2_CAPTURE_VAL=0XFFFF;
                }else TIM2CH2_CAPTURE_STA++;
            }
        }
        if(tsr&0x04)// Capture 2 A capture event occurred
        {
            if(TIM2CH2_CAPTURE_STA&0X40) // Captures a falling edge
            {
                TIM2CH2_CAPTURE_STA|=0X80;         // Mark that a high level pulse width was successfully captured
                TIM2CH2_CAPTURE_VAL=TIM2->CCR2;  // Gets the current capture value.
                TIM2->CCER&=~(1<<5);                   //CC2P=0 Set to rising edge capture
            }
        else // Not yet started, first capture rising edge
        {
            TIM2CH2_CAPTURE_STA=0;    // Empty
            TIM2CH2_CAPTURE_VAL=0;
            TIM2CH2_CAPTURE_STA|=0X40;       // The flag captures the rising edge
            TIM2->CNT=0;                                     // The counter is cleared
            TIM2->CCER|=1<<5;                        //CC2P=1 Set to falling edge capture
        }
        }
    }
    TIM2->SR=0; // Clears the interrupt flag bit
}

Experimental phenomenon

The Ultrasonic.hex file generated by the project compilation is located in the OBJ folder of Ultrasonic project. The corresponding Ultrasonic.hex file is found and the program is downloaded into the development board by using FlyMcu software.

After successful download: Serial port will print Ultrasonic Class! After hardware initialization Then control LED status switch and print obstacle distance every 500ms.


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When using the serial port debugging Assistant, pay attention to the serial port Settings. Incorrect Settings may cause inconsistency