I've gotten some help from a friend but it still is not clear to me and I hate to keep bugging someone.

Simple question really: When I run the below application, the goal is to use time to delay something from happening and then again to make that thing happen for a specified duration. In the case of the demo application, it senses an object. If that object remains in range for 4 seconds, it activates an LED for 5 seconds.

It works and it doesn't. I can change the duration of wait and of enabled but time isn't really right. And, if I remove my delay(500) at the end of the loop, it really fires up and it is like time doesn't exist. I'm looking for a little insight into what I either don't understand and or am doing incorrectly. I can fake it but I'd like it to be accurate.

Code in it's entirety, comments in black.

//----Setup OLED Display ----//

#include <SPI.h>

#include <Wire.h>

#include <Adafruit_GFX.h>

#include <Adafruit_SSD1306.h>

#define OLED_RESET 4 // Reset pin # (or -1 if sharing Arduino reset pin)

#define SCREEN_WIDTH 128 // OLED display width, in pixels

#define SCREEN_HEIGHT 32 // OLED display height, in pixels

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire, OLED_RESET);

#define SCREEN_ADDRESS 0x3C ///< See datasheet for Address; 0x3D for 128x64, 0x3C for 128x32

​

//Initialize I/O pins

int trigger_Pin = 8;

int echo_Pin = 9;

int fanRelay = 5;

int greenLed = 10;

int yellowLed = 3;

int redLed = 2;

Here's where the variables get setup

//Setup Fan Distance and Timer

float fanCountDown = 0.0; //float vs int - not sure I _need_ float but I see no harm

float fanOnSeconds = 0.0;

int minFanOnInches = 0;

int maxFanOnInches = 0;

​

//Default Vehicle State

bool isCarHome = false;

Here's where the value of the timed delay is set.

//Keep Fan From Coming On Immediately (ie: walking in range while the car is away)

float fanDelayCountDown = 0.0;

float fanDelaySeconds = 4.0;

bool isFanDelayApplied = false;

​

// for ultrasonic calcs

int inches = 0; // I'm an American...

int cm = 0;

​

//setup Ultrasonic sensor

long readUltrasonicDistance(int triggerPin, int echoPin)

{

pinMode(trigger_Pin, OUTPUT);

// Clear the trigger

digitalWrite(trigger_Pin, LOW);

delayMicroseconds(2);

// Sets the trigger pin to HIGH state for 10 microseconds

digitalWrite(trigger_Pin, HIGH);

delayMicroseconds(10);

digitalWrite(trigger_Pin, LOW);

pinMode(echo_Pin, INPUT);

// Reads the echo pin, and returns the sound wave travel time in microseconds

return pulseIn(echo_Pin, HIGH);

}

​

void setup() {

Serial.begin(9600); //Initialize Serial communication

// Pin and display setup

pinMode(echo_Pin, INPUT); //Echo pin as Input

pinMode(trigger_Pin, OUTPUT); //Trigger pin as Output

pinMode(fanRelay, OUTPUT); //LED represents fan

pinMode(redLed, OUTPUT);

pinMode(yellowLed, OUTPUT);

pinMode(greenLed, OUTPUT);

display.begin(SSD1306_SWITCHCAPVCC, 0x3C);

display.clearDisplay();

​

//OLED First run "Booting..."

display.clearDisplay();

display.setTextSize(1);

display.setTextColor(WHITE);

display.setCursor(0,0); //left, top

display.println("Status");

display.setTextSize(2);

display.setCursor(0,10); //left, top

display.println("Booting...");

display.display();

delay(3000);

}

​

//Let's get started...

void loop() {

//Fan Distance and Duration Variables

minFanOnInches = 5; // test value

maxFanOnInches = 10; // test value

This is where the run time value is set

fanOnSeconds = 5; // test value, actual is 15min / 900000MS

//measure distance and convert to cm

digitalWrite(trigger_Pin, LOW);

digitalWrite(trigger_Pin, HIGH);

cm = 0.01723 * readUltrasonicDistance(echo_Pin, echo_Pin);

​

// convert to inches by dividing by 2.54

inches = (cm / 2.54);

digitalWrite(trigger_Pin, LOW);

​

// LED INDICATOR LOGIC

//check distance and light LED indicators

//If car is out of range

if (inches > maxFanOnInches){

digitalWrite(yellowLed, HIGH);

} else {

digitalWrite(yellowLed, LOW);

}

//If car is in range to start fan

if (inches <= maxFanOnInches && inches >= minFanOnInches){

digitalWrite(greenLed, HIGH);

} else {

digitalWrite(greenLed, LOW);

}

​

//If car is home and fan should not start

if (inches < minFanOnInches){

digitalWrite(redLed, HIGH);

} else {

digitalWrite(redLed, LOW);

}

// FAN RELAY LOGIC

// Check if car within range...

​

// ------- Car is home -------------

if (inches <= maxFanOnInches && inches >= minFanOnInches){

// 1. Start fan delay count down

if (! isFanDelayApplied) {

isFanDelayApplied = true;

fanDelayCountDown = fanDelaySeconds;

}

// 2. Car is here, start fan run count down

else if (! isCarHome && fanDelayCountDown == 0)

{

// Turn On Fan and Init Count Down Timer

digitalWrite(fanRelay, HIGH);

​

//Timer amd CarStatus

fanCountDown = fanOnSeconds;

isCarHome = true;

​

//OLED Fan On"

display.clearDisplay();

display.setTextSize(1);

display.setTextColor(WHITE);

display.setCursor(0,0); //left, top

display.println("Countdown Running");

display.setTextSize(2);

display.setCursor(0,10); //left, top

display.print("Fan is on");

display.display();

}

}

// -------------- Car is away ---------------

else {

isCarHome = false;

isFanDelayApplied = false;

fanDelayCountDown = 0;

}

// Count down delay timer

if (fanDelayCountDown > 0) {

fanDelayCountDown--;

}

// Count Down Fan Timer

if (fanCountDown > 0) {

fanCountDown--;

}

// Turn Off Fan

else {

digitalWrite(fanRelay, LOW);

//OLED Fan State.

display.clearDisplay();

display.setTextSize(1);

display.setTextColor(WHITE);

display.setCursor(0,0); //left, top

display.println("Status");

display.setTextSize(2);

display.setCursor(0,10); //left, top

display.println("Fan is off");

display.display();

}

// Display variable values in serial console for testing

Serial.print(" fan = ");

Serial.print( digitalRead(12) );

Serial.print(" isCarHome = ");

Serial.print(isCarHome);

Serial.print(" inches = ");

Serial.print(inches);

Serial.print(" fanCountDown = ");

Serial.print(fanCountDown);

Serial.print(" fanDelayCountDown = ");

Serial.print(fanDelayCountDown);

Serial.print(" isFanDelayApplied = ");

Serial.println(isFanDelayApplied);

And here's a delay I have at the end of the loop. I intended to remove it but... then time has no meaning.

// Pause for a second

delay(500); // Wait for 500 millisecond(s)

}

Anyhow, I'm trying to learn and if someone can tell me what I'm not getting, that would be appreciated. Thanks.