I'm researching how to write a sketch that measures subsequent temperature sensor readings from the same sensor, compares the two reading, and if the second reading is 6.7*C or greater than the first reading, set an LED HIGH as an alert.
I've seen recommendations that essentially say, read a currentTemp, compare it to the previousTemp then set up the if statement and action clause. If the difference is met, do something. Otherwise, replace the currentTemp with previousTemp, delay and loop. Seems simple enough.
Here's where I'm confused. If, on first run, there is no properly established previousTemp, does it = 0 by default? And if so, if the first properly measured currentTemp reads 25*C, the if condition is met. Wouldn't the LED go HIGH, at least for the first delay duration? If this is indeed true, is there a way to a minimum of 3 readings (0, first reading, second reading) must be met before applying the if statement? Is there a better way to disregard the first comparison?
Here's what I have so far. Your input/recommendations are greatly appreciated.
// Declare the variables
int currentTemp;
int previousTemp;
int difference;
int ldrPin;
int LED=8;
void setup() {
Serial.begin(9600); // Initialize serial comms
}
void loop() {
currentTemp = analogRead(ldrPin); // Read currentTemp
difference = currentTemp - previousTemp; // Compare currentTemp to previousTemp to gauge rate of change
Serial.println(difference); // Not functionally necessary. Just writes the differential to the Serial Monitor for debug
if (abs(currentTemp >= previousTemp + 6.7)) { // If difference in temps are greater than or equal to 6.7, perform the clause. Use abs to ensure change is only positive temp change.
digitalWrite (LED, HIGH); // Fire up the LED alert
}
previousTemp = currentTemp; // Replace previousTemp with currentTemp
delay(60000); // Wait 60s and loop
}