SparkFun Forums

[ISFJ]

Hi, I'm new to Arduino and am currently using it for my Final Year Project in my university. I proposed to come up with an Intelligent Car Park system where drivers can check for availability of parking berths in a car park wirelessly using their mobile devices.

I am now working on the programming on Arduino, and am faced with a situation. I currently have 2 PIR sensors in my circuit, and I wish to have them both work simultaneously. However, I can only get readings from either one of the sensors at one particular time in the Serial Monitor. I suspect it is because I put the coding for the functionality of both sensors in one loop as shown in the coding below.

Code: Select all

void loop(){

     if(digitalRead(pirPin1) == HIGH){
       digitalWrite(ledPin1, HIGH);   //the led visualizes the sensors output pin state
       if(lockLow){  
         //makes sure we wait for a transition to LOW before any further output is made:
         lockLow = false;            
         Serial.println("---");
         Serial.print("Motion detected at Sensor 1 at ");
         Serial.print(millis()/1000);
         Serial.println(" sec"); 
         delay(50);
         }         
         takeLowTime = true;
       }

     if(digitalRead(pirPin1) == LOW){       
       digitalWrite(ledPin1, LOW);  //the led visualizes the sensors output pin state

       if(takeLowTime){
        lowIn = millis();          //save the time of the transition from high to LOW
        takeLowTime = false;       //make sure this is only done at the start of a LOW phase
        }
       //if the sensor is low for more than the given pause, 
       //we assume that no more motion is going to happen
       if(!lockLow && millis() - lowIn > pause){  
           //makes sure this block of code is only executed again after 
           //a new motion sequence has been detected
           lockLow = true;                        
           Serial.print("Motion ended at Sensor 1 at ");      //output
           Serial.print((millis() - pause)/1000);
           Serial.println(" sec");
           delay(50);
           }
       }
       if(digitalRead(pirPin2) == HIGH){
       digitalWrite(ledPin2, HIGH);   //the led visualizes the sensors output pin state
       if(lockLow){  
         //makes sure we wait for a transition to LOW before any further output is made:
         lockLow = false;            
         Serial.println("---");
         Serial.print("Motion detected at Sensor 2 at ");
         Serial.print(millis()/1000);
         Serial.println(" sec"); 
         delay(50);
         }         
         takeLowTime = true;
       }

     if(digitalRead(pirPin2) == LOW){       
       digitalWrite(ledPin2, LOW);  //the led visualizes the sensors output pin state

       if(takeLowTime){
        lowIn = millis();          //save the time of the transition from high to LOW
        takeLowTime = false;       //make sure this is only done at the start of a LOW phase
        }
       //if the sensor is low for more than the given pause, 
       //we assume that no more motion is going to happen
       if(!lockLow && millis() - lowIn > pause){  
           //makes sure this block of code is only executed again after 
           //a new motion sequence has been detected
           lockLow = true;                        
           Serial.print("Motion ended at Sensor 2 at ");      //output
           Serial.print((millis() - pause)/1000);
           Serial.println(" sec");
           delay(50);
           }
       }
       
  }

If both sensors detect motion at a particular time, eg. at 100 seconds, only readings from a sensor can be obtained on the Serial Monitor. I tried separating the coding for the functionality of each sensor into one loop in itself, but I realized Arduino programming only allows one loop in a program. Hence, I'd like to know if there is any way I can separate the coding, or if there is any way I can get readings from both sensors at one time.

Thank you in advance for your help

[Joeisi]

Parallel Processing? Not in arduino. You could however use interrupts.

[Mee_n_Mac]

To elaborate on the above ... you can have both PIR sensors go to digi inputs that run into interrupt pins and even when they happen simultaneously (or nearly so), be sure that both (one then the other) get processed.

[Philba]

I think part of your problem is you use one variable to ensure both inputs go low. It seems clumsy to do it that way anyway. I'd use a finite state machine technique. http://en.wikipedia.org/wiki/Finite-state_machine gives a decent treatment of this technique. done right, it takes very little code.

Interrupts are the superior way to go (and can be used to drive an FSM).

[fll-freak]

The subject of FSMs has come up a bunch of times in recent history. Perhaps an Arduino centric tutorial might be in order?!

[KeithB]

The snarky answer is:
http://arduino.cc/en/Reference/SwitchCase

Actually, while they don't call it that, the new SolderTime watch is a good example:
http://spikenzielabs.com/SpikenzieLabs/ ... ime_2.html

(Scroll past the assembly instructions!)