Traffic Sign Design

Question

You are asked to design a Traffic sign using a PIC16F877A, 3 LEDs, one Seven Segment Display and one Buzzer. The green LED must be connected to PORTB0, the yellow LED must be connected to PORTB1, and the red LED must be connected to PORTB2. You must connect the buzzer to PORTB3. Finally, you have a cathode type Seven Segment Display that must be connected to the pins of PORTD. Here is how your traffic sign is supposed to work:

(1)   You start at the Green state, where the cars pass and the pedestrians stop. In this state, you stay for 9 seconds. Here, the green LED must be on, and the red and yellow LEDs must be off. Your Seven segment display must show the remaining time in seconds in this state.

(2)   After 9 seconds passes in Green State, you now move on to the Yellow State. In this state you stay for 3 seconds. Here, the yellow LED must be on, and the green and red LEDs must be off. Similar to the Green state, your seven segment display must show the remaining time in the Yellow State.

(3)   After 3 seconds passes in the Yellow state, you now move on to the Red State, where the cars stop and the pedestrians cross the street. In this state you stay for 7 seconds. Here, the red LED must be on, and the green and yellow LEDs must be off. In this state your seven segment display must show the remaining time. But additionally, you will also turn the buzzer on for 500ms of each second so that the disabled people will know that the red light is on for the cars and that they may now cross the street. Notice that the buzzer is on for 500ms and off for 500ms of each second. This continues for the entire duration of the 7 seconds you must spend in the red state.

(4)   You now go back to the Green state and repeat steps 1-3 given above.

First, draw the circuit diagram of your design. Show your MCU and the peripheral devices, and how they are connected to PIC16F877A. You will write your code in C. You may assume the existence of a function named “Delay500ms()” that will make you wait for 500ms. You may also assume that you have a function named “GetCode(int val)” that will return you the bit sequence you must send to the seven segment display to display a value between 0-9.

Answer 1

You will need at least FOUR (4) Timers.....

TimerMain has interval of 9000ms, 7000ms, or 3000 ms

to control the state of the LEDs

TimerBuzzer has interval of 500, to control the buzzer

TimerOneShot has interval of 2000

TimeCountdown has interval of 1000 to control the time remaining

If you cannot change the timer interval of the timers then you will need SIX (6)

timers: timerRED, timerYELLOW, timerGREEN, timerBUZZER, timerOneSHot, timerCountDown

You will also need to store the value of the Countdown, 7,6,5,4,3,2,1 in a register.

You may also need to store the value of along STATE of the program: 0=red, 1=yellow, 2=green,

which is MOD 3....

if so, then on each main timer event, STATE=(STATE+1) mod 3

Although I do not have the hardware for this embedded system, here is the logic behind the timer events.

//****************** 'Initial Startup

Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load

redLight.Visible = False

yellowLight.Visible = False

greenLight.Visible = True

LabelBuzzer.Visible = False

TimerMain.Interval = 9000

TimerMain.Enabled = True

TimerBuzzer.Enabled = False

LabelBuzzer.Visible = False

TimerCountdown.Interval = 1000

TimerCountdown.Enabled = True

TimerOneShot.Interval = 2000

TimerOneShot.Enabled = True

iCount = 7

End Sub

Private Sub TimerMain_Tick(sender As System.Object, e As System.EventArgs) Handles TimerMain.Tick

If (redLight.Visible) Then

redLight.Visible = False

yellowLight.Visible = True

TimerMain.Interval = 3000

TimerBuzzer.Enabled = False

LabelBuzzer.Visible = False

TimerCountdown.Enabled = False

LabelCountdown.Visible = False

ElseIf (yellowLight.Visible) Then

yellowLight.Visible = False

greenLight.Visible = True

TimerMain.Interval = 9000

TimerOneShot.Enabled = True

Else

greenLight.Visible = False

redLight.Visible = True

TimerMain.Interval = 7000

TimerBuzzer.Interval = 500

TimerBuzzer.Enabled = True

LabelBuzzer.Visible = True

End If

End Sub

Private Sub TimerBuzzer_Tick(sender As System.Object, e As System.EventArgs) Handles TimerBuzzer.Tick

If LabelBuzzer.Visible = True Then

LabelBuzzer.Visible = False

Else

LabelBuzzer.Visible = True

End If

End Sub

Private Sub TimerOneShot_Tick(sender As System.Object, e As System.EventArgs) Handles TimerOneShot.Tick

TimerOneShot.Enabled = False

TimerCountdown.Enabled = True

LabelCountdown.Text = 7

LabelCountdown.Visible = True

End Sub

Private Sub TimerCountdown_Tick(sender As System.Object, e As System.EventArgs) Handles TimerCountdown.Tick

LabelCountdown.Text = iCount

iCount = iCount - 1

If (iCount = 0) Then iCount = 7

End Sub