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--- de:examples:sensor:ultrasonic [2009/09/20 14:11] – mikk.leini
+++ de:examples:sensor:ultrasonic [2020/07/20 12:00] (current) – external edit 127.0.0.1
@@ Line 1: / Line 1: @@
+====== Ultraschall Entfernungs-Messung ======
+SRF04 Beispiel
+  * Trigger (blauer Draht) ist mit PB2 verbunden
+  * Echo (gelber Draht) ist mit PB3 verbunden
+  * Roter und schwarzer Draht sind +5V Versorgungs-Spannung
+{{examples:sensor:ultrasonic.jpg?500|}}
+<code c>
+//
+// SFR04 ultrasonic distance measuring
+//
+// Mikk Leini
+// Department of Mechatronics
+// Tallinn University of Technology
+//
+// NB!
+// CPU clock has to be 14745600 hz
+//
+// 2009
+//
+// Include avrlibc
+#include <avr/io.h>
+#include <avr/interrupt.h>
+// Include common library
+#include <stdlib.h>
+#include "pin.h"
+#include "lcd.h"
+// Configuration
+#define INTEGRATION_STEP 5
+// Math operations
+#define MIN(a, b)   ((a) < (b) ? (a) : (b))
+#define MAX(a, b)   ((a) > (b) ? (a) : (b))
+#define INTEGRATE(value, new_value, n)  value = (value * (n - 1) + new_value) / n;
+// Configure pins
+#define LEDR                       PORTPIN(C, 5)
+#define US_TRIGGER                 PORTPIN(E, 5)
+#define US_ECHO                    PORTPIN(E, 4)
+// Ultrasonic data structure
+struct
+{
+	unsigned char state;
+	unsigned long front;
+	unsigned short result;
+} ultrasonic;
+// 16 bit timestamp
+volatile unsigned long timestamp = 0;
+//
+// Start measuring timer
+//
+void clock_init(void)
+{
+	// Fast PWM, Top = ICR, Prescaler = 1
+	TCCR1A = BIT(WGM11);
+	TCCR1B = BIT(WGM13) | BIT(WGM12) | BIT(CS10);
+	// Adjust timer period so that we get 1cm of
+	// measured distance every overflow.
+	//
+	// Formula:
+	// Timer period = clock rate / speed of sound in centimeters * 2
+	// The period is multiplied by 2 because the sound travels
+	// forth and back.
+	ICR1 = 893;
+	// Enable overflow interrupt
+	TIMSK = BIT(TOIE1);
+}
+//
+// Delay
+// Time in ~60 of microseconds
+//
+void delay(unsigned int time)
+{
+	unsigned long end_time, temporary = 0;
+	// Interrupt safe timestamp waiting
+	cli();
+	end_time = timestamp + time;
+	sei();
+	while (temporary < end_time)
+	{
+		cli();
+		temporary = timestamp;
+		sei();
+		asm volatile ("nop");
+	}
+}
+//
+// Timer1 overflow interrupt
+//
+ISR(TIMER1_OVF_vect)
+{
+	timestamp++;
+}
+//
+// Ultrasonic initialization
+//
+void ultrasonic_init(void)
+{
+	// Initial state
+	ultrasonic.state  = 0;
+	ultrasonic.result = 0;
+	// Setup pins
+	pin_setup_output(US_TRIGGER);
+	pin_setup_input(US_ECHO);
+	// External interrupt on any logical change
+	EICRB = BIT(ISC40);
+	// Enable external interrupt 4
+	EIMSK = BIT(INT4);
+}
+//
+// Trigger ultrasonic pulse
+//
+void ultrasonic_trigger(void)
+{
+	// Cannot trigger when listening
+	if (ultrasonic.state > 0)
+		return;
+	// Trigger ultrasonic pulse
+	ultrasonic.state = 1;
+	pin_set(US_TRIGGER);
+	delay(1);
+	pin_clear(US_TRIGGER);
+}
+//
+// External interrupt - on echo pulse
+//
+ISR(INT4_vect)
+{
+	unsigned char b;
+	pin_get_value(US_ECHO, b);
+	// Rising edge ?
+	if (b && (ultrasonic.state == 1))
+	{
+		ultrasonic.front = timestamp;
+		ultrasonic.state = 2;
+	}
+	// Falling edge ?
+	else if (!b && (ultrasonic.state == 2))
+	{
+		ultrasonic.result = timestamp - ultrasonic.front;
+		ultrasonic.state = 0;
+	}
+}
+//
+// Get ultrasonic result
+//
+unsigned short ultrasonic_getresult(void)
+{
+	unsigned short result;
+	// Interrupt safe result reading
+	cli();
+	result = ultrasonic.result;
+	sei();
+	asm volatile ("nop");
+	return result;
+}
+//
+// Program entrance function
+//
+int main(void)
+{
+	unsigned short value = 0;
+	char buffer[8];
+	// Initializing
+	clock_init();
+	ultrasonic_init();
+	pin_setup_output(LEDR);
+	// Init display
+	lcd_init(LCD_DISP_ON);
+	lcd_gotoxy(0, 0);
+	lcd_puts("Distance: ");
+	// Enable global interrupts
+	sei();
+ 	// Endless loop
+	while (1)
+	{
+		// Blink LED constantly
+		cli();
+		pin_set_to(LEDR, (timestamp % 10000) > 1000);
+		sei();
+		// Trigger ultrasonic pulse
+		ultrasonic_trigger();
+		// Read last ultrasonic result
+		INTEGRATE(value, ultrasonic_getresult(), INTEGRATION_STEP);
+		// Go-to first row and to first character
+		lcd_gotoxy(0, 1);
+		// Output text
+		itoa(value, buffer, 10);
+		lcd_puts(buffer);
+		lcd_puts("   ");
+		// Delay a while
+		delay(200);
+	}
+}
+</code>