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improved version for the bateye hardware
// pin definitions
// note: the echoPin has to be a pin which is allowed for interrupts, see here: https://www.arduino.cc/en/Reference/attachInterrupt
const int trigPin = 3;
const int echoPin = 2;
const int ledPin = 13;
const int speakerPin = 9;
// interrupt speed. the datasheet of the HC-SR04 suggests 60 ms, so chose 16 Hz
const float irqSpeed = 16.0;
// updated in the echoInterrupt function
volatile uint32_t echoStart;
volatile uint32_t echoTime;
void setup()
{
// initialize serial communication:
Serial.begin(115200);
// configure pin input and output mode
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(ledPin, OUTPUT);
pinMode(speakerPin, OUTPUT);
// initialize timer1
noInterrupts(); // disable all interrupts
TCCR1A = 0;
TCCR1B = 0;
TCNT1 = 0;
OCR1A = 15625.0f / irqSpeed; // compare match register for IRQ
TCCR1B |= (1 << WGM12); // CTC mode
TCCR1B |= (1 << CS10) | (1 << CS12); // prescaler 1024
TIMSK1 |= (1 << OCIE1A); // enable timer compare interrupt
interrupts(); // enable all interrupts
// attach interrupt to echoPin changes
attachInterrupt(digitalPinToInterrupt(echoPin), echoInterrupt, CHANGE);
}
// start measuring the echo time on rising edge, stop measuring on falling edge and store in echoTime
void echoInterrupt()
{
if (digitalRead(echoPin) == LOW) {
echoTime = micros() - echoStart;
} else {
echoStart = micros();
}
}
// timer 1 interrupt, called with 16 Hz
ISR(TIMER1_COMPA_vect)
{
// test if the echo pin is not asserted (could be if timeout)
if (digitalRead(echoPin) == LOW) {
// send a trigger
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
// output last tone
uint32_t mm = microsecondsToMillimeters(echoTime);
uint32_t pitch = map(mm, 20, 4000, 150, 5000);
if (mm > 4000) {
noTone(speakerPin);
} else {
tone(speakerPin, pitch);
}
}
}
void loop()
{
digitalWrite(ledPin, HIGH);
delay(100);
digitalWrite(ledPin, LOW);
delay(100);
uint32_t mm = microsecondsToMillimeters(echoTime);
Serial.print(mm);
Serial.println();
}
uint32_t microsecondsToMillimeters(uint32_t microseconds)
{
// speed of sound: 340 m/s
return 10 * microseconds / 34 / 2;
}
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