GolamMostafa:
This could be a possible hardware layout for your project.
1. The sensor produces an active low signal. It means that whenever a magnetic material passes nearby the sensor, the sensor output goes LOW. Because, the output of the sensor is open-drain, we need a pull-up resistor to be connected at Terminal-3 which we have done by activating the internal pull-up (Rpin) resisitor of UNO.
2. An I2C type (I2CLCD) has been added to reduce the number of jumper wiring.
3. The signal acquisition and processing algorithm is given below in the form of a Flow Chart. You may take time to convert this Flow Chart into Arduino/C coding. Begin from simple polling method for off time processing of the events and then slowly move to the interrupt method for Real Time processing of the events.
Okay thank you so much for giving me that flowchart and hardware. Actually the issue is (was), taking simultaneous inputs from all sensors (interrupt based), although it worked out that using 2 external interrupts and one pin change interrupt would work fine. What I don't get is, if you use the sensors on pin 10,11,12, that won't do any benefit because neither of the pins are external interrupt pin. The only way you could use all these pins is using pin change interrupt on all of the.
Secondly, I was using a SD card module in this project ( kindly go through another threads), and pins 11,12,13 were supposed to be used with the sd card module.
Thanks again!