Time of Flight Measurement

Time of flight measurement

• A 5V relay is opened, and the electromagnet is exposed. Its driver pin is connected to B0.
• The program makes B0 HIGH, and therefore the electromagnet is energized.
• The user now fixes this relay at a fixed height from the floor/table, and attaches
• a small steel ball to it.
• When the user sends binary number 1 via UART, the relay is turned off and the ball will automatically fall down. It should hit a contact switch made with 2 metal
• plates connected between PA0 and GND.
• The microcontroller starts a timer when the relay is turned off, and stops it when the contact switch
• is triggered, thereby measuring the time taken for the ball to travel the known distance.
• Results are returned via the serial port

The code

examples/C/time_of_flight_uart.c

#include <avr/kp.h>
#include <avr/interrupt.h>
#include <string.h>
#include <stdlib.h>

#define PIN_RELAY 0
#define RELAY_OFF   PORTB |= (1<<PIN_RELAY)
#define RELAY_ON  PORTB &= ~(1<<PIN_RELAY)

#define INPUT_HIGH  PINA&(1<<0)

#define PIN_GREEN 5
#define GREEN_ON   PORTD |= (1<<PIN_GREEN)
#define GREEN_OFF  PORTD &= ~(1<<PIN_GREEN)


int main(void)
{
char buffer[50],cnt;
uint32_t x;
double distance=0;

uart_init(38400);
DDRA=0;  PORTA=1; //input. switch for detecting ball
DDRB=1; // output. for controlling the relay

DDRD=(1<<PIN_GREEN);

while(1){
	RELAY_ON;
	while(!(UCSRA & (1 <<RXC)) )//wait for serial input
		{GREEN_ON;delay_ms(20);GREEN_OFF;delay_ms(20);} ;   // Wait for UART and flicker

	if(UDR==1)
		RELAY_OFF;
	else
		continue;
	start_timer();                        // start the timer using Timer/Counter1
	while(INPUT_HIGH) ;   // Wait for the ball to hit the switch between PA0 and GND
	x = read_timer();

	distance = (float)(x)/1000.;           //this is actually the time in mS
	uart_send_string("Time(ms): ");
	ltoa(distance,buffer,10); //10 means decimal.
	for(cnt = 0;buffer[cnt]!='\0';cnt++){
		uart_send_byte(buffer[cnt]);
		if(cnt>12)break;
	}
	uart_send_byte('\n');


	distance = 0.5*981*distance*distance/1000./1000.; // S = 0.5 * g *  t^2

	uart_send_string("Distance(mm): ");
	ltoa(distance*10,buffer,10); //
	for(cnt = 0;buffer[cnt]!='\0';cnt++){
		uart_send_byte(buffer[cnt]);
		if(cnt>12)break;
	}
	uart_send_byte('\n');
    }
}

Serial Monitor Output