tfmini.c

/* ----------------------------------------------------------------------- *
 * Title:         tfmini.c                                                 *
 * Description:   C-code for TFMini Plus                                   *
 *                Tested on BeagleBone AI                                  *
 *                11/6/2019 Sean J. Miller                                 *
 *References:   																				*
 *https://stackoverflow.com/questions/8507810/why-does-my-program-hang-when-opening-a-mkfifo-ed-pipe*
 *https://stackoverflow.com/questions/2988791/converting-float-to-char     *
 * Prerequisites: apt-get libi2c-dev i2c-tools                             *
 *------------------------------------------------------------------------ */
#include <stdio.h>
#include <stdlib.h>
#include <sys/stat.h>
#include <unistd.h>
#include <linux/i2c-dev.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <string.h>
#include <errno.h>

#define I2C_BUS        "/dev/i2c-3" // I2C bus device
#define I2C_ADDR       0x10         // I2C slave address for the TFMini module
int debug=0;

int i2cFile;

void i2c_start() {
   if((i2cFile = open(I2C_BUS, O_RDWR)) < 0) {
      printf("Error failed to open I2C bus [%s].\n", I2C_BUS);
      exit(-1);
   } else {
       if (debug)printf("Opened I2C Bus\n");
   }
   // set the I2C slave address for all subsequent I2C device transfers
   if (ioctl(i2cFile, I2C_SLAVE, I2C_ADDR) < 0) {
      printf("Error failed to set I2C address [%s].\n", I2C_ADDR);
      exit(-1);
   } else {
      if (debug) printf("Set Slave Address\n");
   }
}

float readDistance() {
	//Routine to output the distance to the console

	int distance = 0; //distance
	int strength = 0; // signal strength
	int rangeType = 0; //range scale

	unsigned char incoming[7]; //an array of bytes to hold the returned data from the TFMini.
	unsigned char cmdBuffer[] = { 0x01, 0x02, 7 }; //the bytes to send the request of distance
	
   write( i2cFile, cmdBuffer, 3 );
   usleep(100000);
   read(i2cFile, incoming, 7);

	for (int x = 0; x < 7; x++)
	{
		if (x == 0)
		{
			//Trigger done
			if (incoming[x] == 0x00)
			{
			
			}
			else if (incoming[x] == 0x01)
			{
			
			}
		}
		else if (x == 2)
			distance = incoming[x]; //LSB of the distance value "Dist_L"
		else if (x == 3)
			distance |= incoming[x] << 8; //MSB of the distance value "Dist_H"
		else if (x == 4)
			strength = incoming[x]; //LSB of signal strength value
		else if (x == 5)
			strength |= incoming[x] << 8; //MSB of signal strength value
		else if (x == 6)
			rangeType = incoming[x]; //range scale
	}
	
	float the_return = distance / (12 * 2.54); //convert to feet.
	if ((the_return)<.5) the_return=0;
	if ((the_return)>14) the_return=14;
	return the_return;
}
void recordDistance(float the_distance){
	char buffer[20];
	int ret = snprintf(buffer, sizeof buffer, "%f", (the_distance));
	if (debug) printf("About to open for writing...\n");
	int fp = open("/home/debian/ramdisk/bbaibackupcam_distance", O_WRONLY|O_CREAT,0666);
	if (debug) printf("About to write...%d\n",fp);
	ret=write(fp, buffer, sizeof(buffer));
	close(fp);
	if (debug) printf("Written %d\n",ret);
}
	
void main() {
   float my_distance=0;
   debug=0; //change to 1 to see messages.
   
   if(debug) printf("Starting:\n");
	
	while (1) {
		i2c_start();
	   my_distance = readDistance();
	   if(debug) printf("the_distance: %f\n",my_distance);
	   recordDistance(my_distance);
	   close(i2cFile); 
	   
	   if(debug) printf("Looping.\n");
	   
	   usleep(1000000);
	}
}