Sensor based "Traffic light" for the Pi

/**
 * This program is used to implement a simple "traffic light" based on
 * distance sensors.
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <time.h>
#include <sys/time.h>
#include <sys/types.h>
#include <wiringPi.h>

/**
 * setup structure for the thread
 */
typedef struct _distSetup {
  // id of the sensor
  short id;
  // the trigger pin for the distance sensor
  short gpio_trigger;
  // the echo pin for the distance sensor
  short gpio_echo;
  // the pin for the red (stop) led
  short gpio_led_red;
  // the pin for the green (go) led
  short gpio_led_green;
  // actual distance
  unsigned int distance;
} distSetup;

// get the actual time in microseconds
// currently we dont need the seconds)
typedef unsigned long long u64;
u64 usec(){
  struct timeval tv;
  gettimeofday(&tv, NULL);
  return tv.tv_usec;
}

/**
 * here starts the measuring for one sensor
 */
void*
start_measure(void *arg)
{
  distSetup *ds = (distSetup*)arg;
  u64 startTime, stopTime;
  // init the pins
  pinMode(ds->gpio_trigger, OUTPUT);
  pinMode(ds->gpio_echo, INPUT);
  pinMode(ds->gpio_led_red, OUTPUT);
  pinMode(ds->gpio_led_green, OUTPUT);
  digitalWrite(ds->gpio_trigger, LOW);
  digitalWrite(ds->gpio_led_red, LOW);
  digitalWrite(ds->gpio_led_green, LOW);
  while(1){
    // trigger the measurement
    digitalWrite(ds->gpio_trigger, HIGH);
    delay(1);
    digitalWrite(ds->gpio_trigger, LOW);
    wait for echo
    while(digitalRead(ds->gpio_echo) == 0);
    startTime = usec();
    measure the time
    while(digitalRead(ds->gpio_echo) == 1);
    stopTime = usec();
    stopTime += stopTime > startTime ? 0 : 100000;
    ds->distance = ((stopTime - startTime) / 2)  / 34.3;
    if(ds->distance < 20) {
      digitalWrite(ds->gpio_led_red, HIGH);
      digitalWrite(ds->gpio_led_green, LOW);
    }else{
      digitalWrite(ds->gpio_led_red, LOW);
      digitalWrite(ds->gpio_led_green, HIGH);
    }
    delay(1000);
  }
  return NULL;
}

#define SENSOR_COUNT 3

int
main(int argc __attribute__((unused)), char *argv[] __attribute__((unused)))
{
  pthread_t pid[SENSOR_COUNT];
  distSetup myDistSetup[SENSOR_COUNT];
  /** setup for the first sensor */
  myDistSetup[0].id = 1;
  myDistSetup[0].gpio_trigger = 8;     // GPIO 00 - PIN 3
  myDistSetup[0].gpio_echo = 9;        // GPIO 01 - PIN 5
  myDistSetup[0].gpio_led_red = 7;     // GPIO 04 - PIN 7
  myDistSetup[0].gpio_led_green = 15;  // GPIO 14 - PIN 8
  /** setup for the second sensor */
  myDistSetup[1].id = 2;
  myDistSetup[1].gpio_trigger = 0;     // GPIO 17 - PIN 11
  myDistSetup[1].gpio_echo = 2;        // GPIO 21 - PIN 13
  myDistSetup[1].gpio_led_red = 3;     // GPIO 22 - PIN 15
  myDistSetup[1].gpio_led_green = 4;   // GPIO 23 - PIN 16
  /** setup for the third sensor */
  myDistSetup[2].id = 3;
  myDistSetup[2].gpio_trigger = 12;    // GPIO 10 - PIN 19
  myDistSetup[2].gpio_echo = 13;       // GPIO 09 - PIN 21
  myDistSetup[2].gpio_led_red = 14;    // GPIO 11 - PIN 23
  myDistSetup[2].gpio_led_green = 10;  // GPIO 08 - PIN 24

  wiringPiSetup();

  if(daemon(0, 0) != 0){
    fprintf(stderr, "Cant daemonize\n");
    return 1;
  }
  {
    FILE *fd = fopen("/var/run/tsl.pid", "w");
    fprintf(fd, "%ld", getpid());
    fclose(fd);
  }
  int i;
  for(i = 0; i < SENSOR_COUNT; i++){
    pthread_create(&(pid[i]), NULL, start_measure, &(myDistSetup[i]));
  }
  while(1){
    FILE *stats = fopen("/var/www/html/ampel.txt","w");
    fprintf(stats, "%d,%d,%d", myDistSetup[0].distance > 20 ? 0 : 1, myDistSetup[1].distance > 20 ? 0 : 1, myDistSetup[2].distance > 20 ? 0 : 1);
    fclose(stats);
    sleep(1);
  }
  for(i = 0; i < SENSOR_COUNT; i++){
    void *ret;
    pthread_join(pid[i], &ret);
  }
  return 0;
}