A small snippet of code that turns on and off three solenoid valves via an Arduino. The test code turns on three valves for two seconds each.

demo.ino

/*
 * Test app that turns three solenoid valves on at set intervals and duration over a
 * set time period
 */

// The time to test the current time against
long startTime = 0;

// Poorly named variable - the time before the timer resets itself back to '0'
long dayLength = 6000;

// How long each valve turns on for
long duration = 2000;

// Info about each valve
int valve1= 10;
long valve1StartTime = 0;
boolean valve1On = false;
boolean valve1Finished = false;

int valve2= 11;
long valve2StartTime = 2000;
boolean valve2On = false;
boolean valve2Finished = false;

int valve3= 12;
long valve3StartTime = 4000;
boolean valve3On = false;
boolean valve3Finished = false;

void setup() {   
  Serial.begin(9600);  
  
  // Set all pins to output only
  pinMode(valve1, OUTPUT);     
  pinMode(valve2, OUTPUT);     
  pinMode(valve3, OUTPUT);   

  // Initialise our starttime
  startTime = millis();
}

// FOREVER
void loop() {
  // Where we at?
  long currentTime = millis();
  
  Serial.print("Current time: ");
  Serial.println(currentTime);
  
  Serial.print("Start time: ");
  Serial.println(startTime);
  
  checkLed1(currentTime);
  checkLed2(currentTime);
  checkLed3(currentTime);
  
  if (currentTime > (startTime + dayLength)) {
    // Let's start the timer again
    resetDay();
  }
  
  delay(100);
}

// Below are the functions that test when we should turn a valve on or off. Yeah,
// I know, this can probably be simplified to a loop and a single function but fuck
// it. I don't enjoy this C stuff

void checkLed1(long currentTime) {
  if (currentTime >= (startTime + valve1StartTime) && 
     currentTime <= (startTime + valve1StartTime + duration)) {
    Serial.println("Turn on 1");           
    digitalWrite(valve1, HIGH); 
  }
  
  if (currentTime >= (startTime + valve1StartTime + duration)) {
    Serial.println("Turn off 1");           
    digitalWrite(valve1, LOW); 
  }
}

void checkLed2(long currentTime) {
  if (currentTime >= (startTime + valve2StartTime) && 
     currentTime <= (startTime + valve2StartTime + duration)) {
    Serial.println("Turn on 2");           
    digitalWrite(valve2, HIGH); 
  }
  
  if (currentTime >= (startTime + valve2StartTime + duration)) {
    Serial.println("Turn off 2");           
    digitalWrite(valve2, LOW); 
  }
}

void checkLed3(long currentTime) {
  if (currentTime >= (startTime + valve3StartTime) && 
     currentTime <= (startTime + valve3StartTime + duration)) {
    Serial.println("Turn on 3");           
    digitalWrite(valve3, HIGH); 
  }
  
  if (currentTime >= (startTime + valve3StartTime + duration)) {
    Serial.println("Turn off 3");           
    digitalWrite(valve3, LOW); 
  }
}

// Resets our timer
void resetDay() {
  Serial.println("Resetting day");   
  valve1On = false;
  valve1Finished = false; 
  
  // Re-init the start time
  startTime = millis();
  
  Serial.print("Start set to: ");
  Serial.println(startTime);
}

Initially this was created so that I could have my three irrigation lines in my garden turn on/off at set times during the course of a day. Hence the variable names like dayLength etc