 void setup() {
   lcd.begin(16, 2);
   lcd.clear();
+
   pinMode(START_SENSOR, INPUT);
   pinMode(END_SENSOR, INPUT);
   Serial.begin(9600);      // open the serial port at 9600 bps:

#include <LiquidCrystal.h>

#define END_SENSOR A1
#define START_SENSOR A2
#define SENSOR_LOW 0
#define SENSOR_HIGH 150 //250
// sensor % is used
// as a multiplier against the ambient
// light
#define SENSOR_PCT 0.8

    elapsed_time = endtime - starttime;

    // debounce finished sensor
    // probably not strictly necessary
    while (finished) {
      finished = sensor_tripped(END_SENSOR, SENSOR_LOW, sensor_high_end);
    }
