Arduino + sim800l + dht11

Question

I am trying to make a call only once. But it is calling over and over. Code is If(t>20){ Sim800l.println(ATD +phone number)} How can I make it to call me once only? I just need to inform me if temperature is over 20°C. Using dht11, arduino uno and sim800l.

Answer 1

You could use a flag like so. Everytime the temperature drops below/equal to 20 the flag hasChanged will be set to true. And when the temperature rises above 20, the message will be printed once, and the flag will be toggled off until the next time the temperature drops.

// you'll have to adjust the syntax to meet your language needs

bool hasChanged = true;
if (t>20 && hasChanged) {
   // this block happens once everytime the temperature surpasses 20
   Sim800l.println(ATD +phone number);
   hasChanged = false;
} else {
   hasChanged = true;
}