File content as of revision 2:b47f8dbf374c:

// Scalextric Timer for Ada Lovelace Day
//
// Uses Nucleo board F072 with LCD Keypad shield
// Connect D3 to Trig & D2 to Echo
// Connect VCC to 5V (pin CN7 18)
// Connect GND to 0V (pin CN7 19)

#include "mbed.h"
#include "hcsr04.h"     // Ultrasonic sensor
#include "TextLCD.h"    // LCD1602

// serial PC for debug
Serial pc(SERIAL_TX, SERIAL_RX);
// Ultrasonic sensor
HCSR04  usensor(D3,D2);  // Trig, Echo

// LCD Shield
TextLCD lcd(D8, D9, D4, D5, D6, D7);   // used to drive display
AnalogIn keys(A0);                     // used to sample buttons

Timer lap_timer;
Timer wait_timer;

// Subroutine to display text on LCD - called from below
// call as follows:
// textLCD(text, line)
// where text = up to 16 characters of text
// line = line 0 or 1 on the LCD; where 0 is the top line and 1 is the bottom line
    
void textLCD(char *text, int line) {

    char tmpBuf[16];
    for (int i = 0; i < 16; i++) tmpBuf[i] = 0x20;
    for (int i = 0; i < strlen(text); i++) {
        if (i < 16) tmpBuf[i] = text[i];
        lcd.locate(i, line);
        lcd.putc(tmpBuf[i]);
    }
}

///////////////////////////////////////////////////////////////////////////////
// Main Program starts here
///////////////////////////////////////////////////////////////////////////////

int main()
{
 
 //// Try changing these:
    // Variables to tune
    float min_laptime = 1.0; // Minimum laptime - time to wait after seeing car before measuring again in seconds
    int sample_time = 100;   // Sample time - time between sampling values from sensor in milliseconds
    int trigger_distance = 2;  // Trigger distance - distance below which the car registers as detected
//// Careful with anything after this though

    // Variables used within the program - set to their initial values
    int dist = 0;
    float lap_time = 0;
    int lap_count = 0;
    float wait_time = min_laptime + 1.0; // ensure larger than minimum lap time for first loop
    
    // Variables used to hold text to display on LCD for correct formatting
    char lap_string[16];
    char laptime_string[16];
    
    // Initialise the serial interface and set its data rate
    pc.baud(9600);

    // Intro Screen
    pc.printf("ARM Sheffield Scalextric Challenge \n"); // Display to Serial Interface
    textLCD("ARM Scalextric ", 0);  // Display on First Line of LCD

    // Main loop - runs foerever
    while(1) {
       // Set up and read ultrasonic sensor after "sample_time"
       usensor.start();
       wait_ms(sample_time);
       dist=usensor.get_dist_cm();  // read sesnsor distance measure 
       pc.printf("Distance %d\n\r", dist);  // Debug - display distance to Serial Interface
       if (lap_count > 0) {   // If not the first lap - read value of wait timer
         wait_time = wait_timer.read();
       }
       if ((dist < trigger_distance) and (wait_time > min_laptime)) { // Spotted something closer than trigger_distance from the sensor and  at least a minimum laptime later
         wait_timer.reset(); // reset the wait timer
         wait_timer.start(); // start the wait timer again
         if (lap_count == 0) {   // First Lap - start lap timer
           lap_timer.reset();
           lap_timer.start();
           pc.printf("Timing... \r");        // Debug to Serial Interface
           textLCD("Timing..........", 1);   // Message to LCD
         } else {                // Completed a lap
           lap_time = lap_timer.read();  // Get time for lap
           lap_timer.reset();
           pc.printf("Lap : %d, Lap time : %f s \r", lap_count, lap_time);  // Debug to Serial Interface
           sprintf(lap_string, "Lap : %d ", (char*)lap_count);      // Format Lap count string
           sprintf(laptime_string, "Lap time : %f s, ", lap_time);  // Format Lap time string
           textLCD("                ", 0);  // Clear top line on LCD
           textLCD(lap_string, 0);          // Display Lap Count on LCD
           textLCD("                ", 1);  // Clear bottom line on LCD
           textLCD(laptime_string, 1);      // Display Lap Time on LCD
        }
        lap_count++;               // Increment lap counter by 1
      }   // end of something spotted
    }     // end of while loop 
}  // end of main program