added demo SRF02 range code and altered it to write to a log file, in…

…cluding microsecond timestamps and the current calibrated minimum range. The min range settles within a couple of seconds

range/rangeOutput

@@ -0,0 +1,301 @@
+time,range,min_range
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range/rpi_srf02.c

@@ -0,0 +1,88 @@
+// SRF02 example coder for the Raspberry pi
+//
+// This code will work for the SRF02/ 10/ 235 and 08.
+// It will take a ranging from the module and print results
+// to the screen.
+//
+// By James Henderson, 2012. 
+// Hacked about slightly by Dav
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <linux/i2c-dev.h>
+#include <fcntl.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/time.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+
+  int fd;                            // File description
+  char *fileName = "/dev/i2c-1";                // Name of the port we will be using
+  int i; 
+  FILE *fdOut; // handle to output file
+  char *outFileName = "rangeOutput";
+  struct timeval t;
+  int address = 0x70;                    // Address of the SRF02 shifted right one bit
+  unsigned char buf[10];                    // Buffer for data being read/ written on the i2c bus
+  unsigned int range;
+  unsigned int minRange;
+
+  if ((fd = open(fileName, O_RDWR)) < 0) {          // Open port for reading and writing
+    printf("Failed to open i2c port\n");
+    exit(1);
+  }
+
+  if (ioctl(fd, I2C_SLAVE, address) < 0) {          // Set the port options and set the address of the device we wish to speak to
+    printf("Unable to get bus access to talk to slave\n");
+    exit(1);
+  }
+  // open our log file and print a header line
+  fdOut = fopen(outFileName, "w");
+  fprintf(fdOut, "time,range,min_range\n");
+
+  for (i=0;i<300;i++) {
+    buf[0] = 0;                          // Commands for performing a ranging
+    buf[1] = 81;
+
+    if ((write(fd, buf, 2)) != 2) {                // Write ping command to the i2c port
+      printf("Error writing to i2c slave\n");
+      exit(1);
+    }
+    usleep(80000);                        // This sleep waits for the ping to come back
+    buf[0] = 0;                          // This is the register we wish to read from
+    if ((write(fd, buf, 1)) != 1) {                // Send the register to read from
+      printf("Error writing to i2c slave\n");
+      exit(1);
+    }
+    if (read(fd, buf, 6) != 6) {                // Read back data into buf[]
+      printf("Unable to read from slave\n");
+      exit(1);
+    }
+    else {
+      // buf[0] software version. If this is 255, then the ping has not yet returned
+      // buf[1] unused
+      // buf[2] high byte range
+      // buf[3] low byte range
+      // buf[4] high byte minimum auto tuned range
+      // buf[5] low byte minimum auto tuned range
+
+      range = (buf[2] <<8) + buf[3];      // Calculate range as a word value
+      minRange = (buf[4] <<8) + buf[5];   // Calculate range as a word value
+    }
+
+    printf("Range was: %u. Minimum: %u\n", range, minRange);
+    gettimeofday(&t, NULL);
+    fprintf(fdOut, "%u.%06d,%u,%u\n", t.tv_sec, t.tv_usec, range, minRange);
+
+    usleep(100000); // wait another 100ms and perform another ranging
+  }   // end for 300
+  close(fd);
+  fclose(fdOut);
+  return 0;
+}
+