AVR based parking system - Simple Arduino Based Automated Parking Lot System - page 13

}
Also, at the exit of the parking, if the paid key is depressed by parking operator, then
the program computes the parking capacity again and if there is a deference between the
older parking capacity and computed capacity, it means one or some cars have exit their
slots and are leaving the parking lot. Then at the entrance gate, the out arm gate is lifted
up to let the driver out. Then one unit is added to parking capacity, and all related vari-
ables of the new vacant space are reset. The output_down_time variable is set and then
until the expiry of 10 seconds, the drivers can leave the parking lot and after that exit arm
gate moves back to its original position and the related motor is turned off when the re-
lated limit switch is activated.
In the timer2 interrupt, a program generates a delay in the gates moving down. When
either input_down_time or output_down_time changes to 1, the related count variable
starts to get incremented. When its value exceeds the defined value, the system brings the
related gate down.