Arduino - My problem is when the condition is greater than 900.00 it will continue the loop and do the code below once

Question

I want is to stop the loop and when it read Greater than 900.00 again it will do task again.

I need condition. When it back to greater than 900.00 the code below will do task and then it will stop. And when it will reach the condition again it will do the code again and it will stop .. Please help me

void loop(){
 float reading = analogRead(LIGHTSENSORPIN); //Read light level
 float square_ratio = reading / 1023.0; //Get percent of maximum value (1023)
 square_ratio = pow(square_ratio, 2.0); //Square to make response more obvious
 analogWrite(LEDPIN, 255.0 * square_ratio); //Adjust LED brightness relatively
 analogWrite(LED_BUILTIN, 255.0 * square_ratio); //Adjust LED brightness relatively
 Serial.println(reading); //Display reading in serial monitor
if(reading >= 900.00){
 digitalWrite(smDirectionPin, LOW); //Writes the direction to the EasyDriver DIR pin. (LOW is counter clockwise).
 /*Turns the motor fast 1600 steps*/ 
 for (int i = 0; i < 400; i++){
 digitalWrite(smStepPin, HIGH);
 delayMicroseconds(700);
 digitalWrite(smStepPin, LOW);
 delayMicroseconds(700);
}
}
 delay(1000);
}

• Gerben: You need to also store the old reading. Then change the if to if(oldReading<900.00 and reading>=900.00)
• kervy hipona: how can i store the old reading??
• Gerben: Please post your code, instead of an image.
• kervy hipona: Sir can u please modify my code to do that?
• kervy hipona: anybody can help?? please..

Answer 1

setup(){ ....
......
}
float old_reading=0;
loop() {
float reading = analogRead(LIGHTSENSORPIN); //Read light level
// ... do this always (maybe empty) 
// in your code it is LED shining and printing
if ((old_reading<=900) && (reading>900)) {
 // ... do this just just once when reading goes over 900 up
 // in your code it is manipulating motor
 }
old_reading=reading;
// ... do this always , but after special part (maybe empty)
// in your code it is just delay
}

• So on begining old_reading is just zero, but being declared outside loop, it keeps its value between different runs of loop.
• the if (condition) does not hit, as reading is less than 900 (if it starts with more then 900, see next part)
• the end with old_reading=reading; makes old_reading to be the last known value of reading
• when reading goes Greater than 900 for first time, the old_reading is Less or Equal 900 (as it was the last value of reading before it crossed 900 up.
• • so the if (condiotion) is true and you start moving motor
• • then (on the end) you set old_reading=reading; and old_reading is also larger then 900
• • while reading stays over 900 in next loops, the old_reading does so, and therefore the if (condition) does not hit - (old_reading<=900) is not true
• • when reading falls down 900 or lower, the if(condition) also does not hit, but after that the old_reading=reading; makes old_reading less or equal 900
• and so we are at the start again, skipping the part after if(condition) until reading gets Greater than 900 (then we run motor, set old_reading to something greater than 900 and we already was here and know, how it works :)

• kervy hipona: Thank you sir gilhad... i appreciate your time and effort doing this.. keep helping others
• gilhad: :) This is just basic programming (not even about Arduino) - you really should read more articles/books about programming and read examples and shorter programs and try to understand it by yourself - it will give much more understanding. I suggest to read arduino.cc and/or other sites about arduino and about programming for beginers. Really pays off in long term :)