I am creating this temp monitoring system - arduino

Question

I am creating this temp monitoring system...Therefore, i want to get messages/alerts when the temperature are below 6 and again when they come back to above 6. Note: I don't want the alert (sendMailNormalValue():wink: to come when the system boots up....How do I deactivate the sendMailNormalValue(); and activate it only when the temp are below 6 (only to alert me when comes back to above 6)..
#include <OneWire.h>
#include <DallasTemperature.h>
// GPIO where the DS18B20 is connected to
const int oneWireBus = 5;
// Setup a oneWire instance to communicate with any OneWire devices
OneWire oneWire(oneWireBus);
// Pass our oneWire reference to Dallas Temperature sensor
DallasTemperature sensors(&oneWire);
//========================================
float t;
int period = 30000;
unsigned long time_now = 0;
bool DisplayFirstTime = true;
int period1 = 30000;
unsigned long time_now1 = 0;
void sendMailBelowValue(){
}
void sendMailNormalValue(){
}
void setup() {
// put your setup code here, to run once:
Serial.begin (9600);
}
void loop() {
// put your main code here, to run repeatedly:
sensors.requestTemperatures();
t = sensors.getTempCByIndex(0);
float p=t-2;
// Check if any reads failed and exit early (to try again).
if (isnan(t)) {
Serial.println("Failed to read from sensor !");
delay(500);
return;
}
if (t>6){
if(millis() > time_now + period){
time_now = millis();
sendMailNormalValue();
Serial.print ("You got messagae");
}
}
if (t<6){
if(millis() > time_now1 + period1 || DisplayFirstTime){
DisplayFirstTime = false;
time_now = millis();
sendMailBelowValue();
}
}
}

Answer 1

I think I understand what you mean. On error (temp < 6), you want to send an email every 30 seconds; when the teperature reaches 6 or mode, send a single email to say the error condition has been fixed. On boot, only send an email if in error.
If that's it, you'll need to keep track of the error condition using a global flag.
// ...
bool tempError; // initialized in setup()
void setup()
{
// ...
float t;
for(;;) // loop until we get a valid reading.
{
t = sensors.getTempCByIndex(0);
if (!isnan(t))
break;
Serial.println("Failed to read from sensor !");
delay(500);
}
tempError = (t < 6);
}
void loop()
{
// read temp and check sensor...
// ...
if (t < 6)
{
tempError = true;
// send error email, set timer, etc...
}
else if (tempError)
{
// temp is now fine, after being too low.
tempError = false; // Clear error flag.
// send OK email, only once.
// Don't forget to clear the 30 second email timer !!!
}
}
Usually, you'd want some hysteresis in an alert system. You should consider waiting some seconds after the temperature has been 'fixed' before sending the 'OK' email. Otherwise you may end up getting lots of fail/fixed emails when the temperature is around 6 degrees. This is usually done with a simple state machine engine, but that is a bit beyond the scope of this questkon.