Page 393 - ARM Based Microcontroller Projects Using MBED

15.7 PROJECT 3—CAR PARK CONTROLLER—USING SIGNALS 379
15.7 PROJECT 3—CAR PARK CONTROLLER—USING SIGNALS

15.7.1 Description
This is a simple car park controller project. It is assumed that the car park has a capacity of
100 cars. Entry and exit gate barriers are available at the car park entry and exit points, respec-
tively. The gate output signals are normally at logic HIGH and they go to logic LOW when a
gate opens to let a car pass through. The controller counts the number of cars inside the car
park and displays messages on the screen to let the drivers know how many spaces are avail-
able inside the car park (if any). The following information is displayed on the screen:
SPACES: nnnn
Initially the card park is assumed to be closed (e.g., at night) and message CLOSED is
displayed. The car park becomes operational when a button called StartButton is pressed.
When the car park is full or when it is closed the entry barrier is locked and does not open
to let any cars into the car park.

15.7.2 Aim
The aim of this project is to show how a car park controller can be designed using a mul-
titasking approach.

15.7.3 Block Diagram

The block diagram of the project is shown Fig. 15.13. It is assumed that barriers with
switches are used at the entry and exit points of the car park. Normally the outputs of these
switches are held at logic HIGH and they become LOW when the barriers are lifted.

15.7.4 Circuit Diagram
The circuit diagram of the project is shown in Fig. 15.14. Entry and exit switches are named
as EntrySwitch and ExitSwitch, respectively and they are connected to GPIO pins PC_0 and
PC_1 as shown in the figure. In this project two push-button switches are used to simulate the
car park barriers. A PC is used to display the car park information.

15.7.5 The PDL
The PDL of the program is shown in Fig. 15.15.

15.7.6 Program Listing

The program listing (program: CarPark) is shown in Fig. 15.16. At the beginning of the pro-
gram, header files mbed.h and rtos.h are included in the program, and the serial PC interface is
defined. EntrySwitch, ExitSwitch,and StartButton are assigned to PC_0, PC_1, and PC_3,