Arduino countdown within delay loop - arduino

Question

What a great learning experience my first Arduino project is turning out to be.. I would now like to add a countdown until a sensor reading is taken and displayed, which will repeat infinitely. I've got the sensor and LCD display working fine but my loop is not quite right.. Should I be using a while() of some sort? How do I keep the timer ticking during the big delay between readings?
/*Code for self-watering plant with LCD readout*/
// value for LCD params
char ESC = 0xFE;
// analog input pin that the soil moisture sensor is attached to
const int analogInPin = A1;
// value read from the soil moisture sensor
int sensorValue = 0;
// if the readings from the soil sensor drop below this number, then turn on the pump
int dryValue;
// countdown timer until next soil reading
int timerValue = 9;
void setup() {
pinMode(12, OUTPUT);
// initialize serial communications at 9600 bps:
Serial.begin(9600);
// Set the "dry" value of soil on turning on the device
dryValue = analogRead(analogInPin);
// pause before intialize LCD
delay(2000);
// Initialize LCD module
Serial.write(ESC);
Serial.write(0x41);
Serial.write(ESC);
Serial.write(0x51);
// Set Contrast
Serial.write(ESC);
Serial.write(0x52);
Serial.write(40);
// Set Backlight
Serial.write(ESC);
Serial.write(0x53);
Serial.write(5);
//print the dry value to serial
Serial.print("Dry = " );
Serial.print(dryValue);
Serial.print(" ");
}
void loop(){
watering();
// wait some time (really should be delay(86400000))
delay(10000);
}
void printTimer(){
// Set cursor line 1, column 16
Serial.write(ESC);
Serial.write(0x45);
Serial.write(0x0F);
// print the timer value
Serial.print(timerValue);
timerValue = timerValue - 1;
if(timerValue == 0){
timerValue = 9;
}
}
void printVal(){
// set cursor line 2, column 1
Serial.write(ESC);
Serial.write(0x45);
Serial.write(0x40);
// print the sensor to the serial monitor:
Serial.print("Sensor = " );
Serial.print(sensorValue);
Serial.print(" ");
printTimer();
}
void watering(){
// read the analog in value:
sensorValue = analogRead(analogInPin);
//turn on the water pump for some time if the soil is too dry
if(sensorValue < dryValue){
digitalWrite(12, HIGH);
delay(2000);
digitalWrite(12, LOW);
}
else {
printVal();
}
}

Answer 1

It's actually really simple: Don't delay. Instead, initialize a timer to run a routine whenever it overflows or hits a certain value. Examine the datasheet for the microcontroller used in your Arduino for the specific bits to frob (note that the Arduino libraries use the timer 0 overflow vector for themselves), and the avr-libc documentation for how to denote the ISR(s) for the timer. Your loop() then becomes a big sleep while the timer runs the entire show for you.

Answer 2

I would use a timer library for Arduino like this http://playground.arduino.cc//Code/SimpleTimer
Just download the library, put it in the "libraries" folder in your sketchbook and restart your Arduino IDE to load the new library.
Then your code would look something like this. Basically what it does it updates the screen every loop and then once every 86400000 ms it checks the "watering" function. Just so you know this code would only check the soil once every 24 hours (86400000ms). I think a better solution would be to constantly check the soil and water anytime it is needed. But Im no gardener so maybe there is a reason for just checking once a day.
#include <SimpleTimer.h>
// the timer object
SimpleTimer timer;
void setup() {
Serial.begin(9600);
timer.setInterval(86400000, watering); // how often you would call your watering function is set with the first variable
}
void loop() {
timer.run();
printTimer();
}
void printTimer(){
// Set cursor line 1, column 16
Serial.write(ESC);
Serial.write(0x45);
Serial.write(0x0F);
// print the timer value
Serial.print(timerValue);
timerValue = timerValue - 1;
if(timerValue == 0){
timerValue = 9;
}
}
void printVal(){
// set cursor line 2, column 1
Serial.write(ESC);
Serial.write(0x45);
Serial.write(0x40);
// print the sensor to the serial monitor:
Serial.print("Sensor = " );
Serial.print(sensorValue);
Serial.print(" ");
printTimer();
}
void watering(){
// read the analog in value:
sensorValue = analogRead(analogInPin);
// send it to the display
printVal();
//turn on the water pump for some time if the soil is too dry
if(sensorValue < dryValue){
digitalWrite(12, HIGH);
delay(2000);
digitalWrite(12, LOW);
}
}