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December 30, 2018 18:59
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Simple arduino HC-SR04 (HCSR04) distance detection using interrupts for low latency measurements
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#include <Arduino.h> | |
// Uses https://github.com/PaulStoffregen/TimerOne for sending on a regular interval | |
#include <TimerOne.h> | |
// ECHO pin, needs to be a pin that supports interrupts! | |
#define ULTRASONIC_PIN_INPUT 2 | |
// TRIG pin, can be any output pin | |
#define ULTRASONIC_PIN_OUTPUT 3 | |
// update interval, make sure to keep it above 20ms | |
#define ULTRASONIC_TIMER_US 50000 | |
// the time the pulse was sent | |
volatile long ultrasonic_echo_start = 0; | |
// the distance once it's been measured | |
volatile long ultrasonic_distance = 0; | |
void ultrasonicPulse(){ | |
// Sets the trigger on HIGH state for 10 micro seconds to send a series of pulses | |
digitalWrite(ULTRASONIC_PIN_OUTPUT, HIGH); | |
// blocks 10 microseconds from the interrupt, I think we'll live :) | |
delayMicroseconds(10); | |
// disable the sending again so we can wait for a response | |
digitalWrite(ULTRASONIC_PIN_OUTPUT, LOW); | |
// record the send time | |
ultrasonic_echo_start = micros(); | |
} | |
void ultrasonicEcho(){ | |
// don't do anything if no pulse has been sent | |
if(ultrasonic_echo_start != 0){ | |
// calculate the distance by measuring how long it took to return the sound | |
// The speed of sound is 343 m/s and we need half the time it took (since | |
// the sound has to travel towards the object _AND_ back). So a single echo does | |
// 1/(343/2) = 0.005831 seconds per meter | |
ultrasonic_distance = (micros() - ultrasonic_echo_start) / 58; | |
ultrasonic_echo_start = 0; | |
} | |
} | |
void setup(){ | |
Serial.begin(115200); | |
// set the echo pin to receive interrupts, on an arduino uno only pin 2 and 3 can link to interrupts | |
pinMode(ULTRASONIC_PIN_INPUT, INPUT_PULLUP); | |
pinMode(ULTRASONIC_PIN_OUTPUT, OUTPUT); | |
// set the update interval for sending the trigger | |
Timer1.initialize(ULTRASONIC_TIMER_US); | |
// link the trigger function to the timer | |
Timer1.attachInterrupt(ultrasonicPulse); | |
// link the echo function to the echo pin | |
attachInterrupt(digitalPinToInterrupt(ULTRASONIC_PIN_INPUT), ultrasonicEcho, RISING); | |
} | |
void loop() { | |
Serial.print("Distance: "); | |
Serial.println(ultrasonic_distance); | |
delay(ULTRASONIC_TIMER_US / 1000); | |
} |
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Aiming to code the same functionality I found this conversation and I thank you for the examples.
I'd like to share my version of the code, where I don't use a timer for the trigger (maybe should be a good pratice...) but I try to improve the accuracy considering only the time between the two echo edges (anyway, the same goal could have been reached by compensating the offset).