fingerprint scanner and GSM module- how do i put a timer condition using if statements?

Question

I am using a fingerprint sensor and GSM module on Arduino MEGA 2560. I want a fingerprint to be scanned every minute, if a minute elapses with no finger scanned, then the next code for the GSM to send an SMS must be executed enter image description here

const unsigned long timeLimit = 60000;
unsigned long prevTime;
unsigned long currTime;
void setup() {
 prevTime = millis();
}
void loop() {
 unsigned long currTime = millis();
 getFingerprintID(); //fingerprint func
 if (currTime - prevTime <= timeLimit) {
 if (finger.fingerSearch() == FINGERPRINT_OK) { //if the fingerprint matches
 prevTime = currTime;
 }
 } else {
 Serial.print("MAXIMUM TIME OF ");
 Serial.print(currTime / 1000);
 Serial.print(" SECONDS HAS LAPSED\n");
 }
}

• Coder_fox: Consider looking at this forum.arduino.cc/t/using-millis-for-timing-a-beginners-guide/… What you need to do is create a timer that every 60 seconds executes the code that you want and sets a flag if it was successful and based on that you can do whatever you need with the GSM.
• jsotola: do something like this ... modify the millis code in the comment from @Coder_fox to increment a counter every second ... the millis code does nothing else ...... check for fingerprint, if detected then clear the counter to zero, do nothing else ...... check the counter, if 60 then send SMS
• Mtho: @Coder_fox the issue i have now is that the timer starts when i run the code and lapses within 60 seconds regardless of how many times the fingerprint was scanned within the time period

Answer 1

i cleaned up your version. make sure to update the prevTime variable.

const unsigned long timeLimit = 60000;
unsigned long prevTime ;
unsigned long currTime;
unsigned long elapsedTime;
int id;
void setup() {
prevTime=millis();
} 
void loop() {
 if (fingerprint()){
 currTime = millis();
 elapsedTime = currTime- prevTime;
 if (elapsedTime < 60*1000) {
 prevTime = currTime;
 } else {
 sendSms();
 }
 }
}
void sendSms() {
Serial.print("MAXIMUM TIME OF ");
Serial.print(currTime/1000);
Serial.print(" SECONDS HAS LAPSED\n");
}
bool fingerprint(){
 bool fingerPrintAccepted = false;
 if (finger.fingerSearch()==FINGERPRINT_OK){
 fingerPrintAccepted = true;
 }
 return fingerPrintAccepted;
}