Ultrasonic Sensor Interrupts Cause Inaccurate Readings on Nucleo Board

Ultrasonic Sensor Interrupts Cause Inaccurate Readings on Nucleo Board

This article discusses the issue of using interrupts to measure distances in loops, which can cause inaccurate readings when using an ultrasonic sensor with a Nucleo board. We will cover key concepts related to this topic, including how interrupts work, how they can affect sensor readings, and possible solutions for obtaining accurate readings.

Interrupts in Microcontrollers

Interrupts in microcontrollers allow external devices or software to temporarily halt the normal execution of a program and trigger a specific function or routine. This feature is particularly useful in applications where real-time responses are required or when handling multiple tasks simultaneously.

Measuring Distance Using Ultrasonic Sensors

Ultrasonic sensors emit sound waves and measure the time it takes for the waves to bounce back after hitting an object. By knowing the speed of sound, the distance to the object can be calculated using the formula: distance = (time × speed of sound) / 2.

Interrupts and Ultrasonic Sensor Readings

Using interrupts in loops to measure distances with an ultrasonic sensor can result in inaccurate readings due to the following factors:

• Overhead: The time it takes for the microcontroller to handle the interrupt and switch to the distance measurement function can introduce errors in the measurement.
• Synchronization: If multiple measurements are taken in quick succession, it can be challenging to synchronize the emission and reception of sound waves accurately.
• Interference: Other active peripherals or processes on the microcontroller can interfere with the sensor readings, leading to inaccuracies.

Possible Solutions

To obtain accurate readings when measuring distances using an ultrasonic sensor and a Nucleo board, consider the following solutions:

• Disable interrupts: Disable interrupts during the distance measurement process to minimize the overhead and synchronization issues. However, this approach may not be suitable for applications where real-time responses are required.
• Use hardware timers: Utilize hardware timers to generate precise time measurements without relying on interrupts. This can help minimize the overhead and improve overall accuracy.
• Increase delay between measurements: Introduce a delay between consecutive measurements to allow sufficient time for the microcontroller to stabilize and minimize interference.

Code Example

The following example demonstrates how to measure distance using an ultrasonic sensor without relying on interrupts. Note that this example assumes the use of the STM32CubeMX library and the appropriate configuration for the ultrasonic sensor and timer.

#include "stm32f4xx_hal.h"

// Define the ultrasonic sensor pin connections
#define TRIG_PIN GPIO_PIN_12
#define ECHO_PIN GPIO_PIN_13
#define TRIG_PORT GPIOB
#define ECHO_PORT GPIOB

// Define the timer used for distance measurements
#define DISTANCE_TIMER TIM2

// Global variables
uint32_t echo_time;
float distance;

int main(void)
{
 // Initialize the ultrasonic sensor pins
 GPIO_InitTypeDef gpio_init_structure;
 gpio_init_structure.Pin = TRIG_PIN | ECHO_PIN;
 gpio_init_structure.Mode = GPIO_MODE_OUTPUT_PP;
 gpio_init_structure.Speed = GPIO_SPEED_FREQ_HIGH;
 HAL_GPIO_Init(TRIG_PORT, &gpio_init_structure);
 HAL_GPIO_WritePin(TRIG_PORT, TRIG_PIN, GPIO_PIN_RESET);

 // Configure the distance measurement timer
 TIM_ClockConfigTypeDef timer_clock_structure;
 TIM_MasterConfigTypeDef timer_master_structure;
 TIM_OC_InitTypeDef timer_oc_structure;

 HAL_TIM_Base_DeInit(DISTANCE_TIMER);
 HAL_TIM_Base_StructInit(&tim_base_init_structure);
 timer_clock_structure.ClockSource = TIM_CLOCKSOURCE_INTERNAL;
 HAL_TIM_Base_Init(DISTANCE_TIMER, &tim_base_init_structure);

 timer_master_structure.MasterOutput
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