Microprocessor Based Traffic Light Control Project

Designing a microprocessor system to control traffic lights is discussed in this post. The traffic light arrangement is as shown in the figure. The trffic should be controlled in the following manner.

Allow traffic from W to E and E to W transition for 20 seconds.
Give transition period of 5 seconds (yellow bulbs ON)
Allow traffic from N to S and S to N for 20 seconds.
Give Transition period of 5 seconds (yellow bulbs ON)
Repeat the process.

Hardware needed for Traffic Light control.

The above figure shows the interfacing diagram to control 12 electric bulbs. Port A is used to ontrol lights on N-S road and port B is used to control lights on W-E road. Actual pin connections are listed in table below.

Pins	Light	Pin	Light
PA0	R1	PB0	R3
PA1	Y1	PB1	Y3
PA2	G1	PB2	G3
PA3	R2	PB3	R4
PA4	Y2	PB4	Y4
PA5	G2	PB5	G4

The electric bulbs are controlled by relays. The 8255 pins are used to control relay on-off action with the help of relay diver circuits. The driver circuit includes 12 transitors to drive 12 relays. The image below shows the interfacing of 8255 to the system.

I/O map:

Ports/control Register	Address Lines A7 A6 A5 A4 A3 A2 A1 A0	Address
Port A Port B Port C Control Register	1    0    0    0    0   0    0     0 1    0    0    0    0   0    0     1 1    0    0    0    0   0    1     0 1    0    0    0    0   0    1     1	80 H 81 H 82 H 83 H

Software needed for Traffic Light control


Control word for initialization of 8255.

BSR/IO	MODE A	PA	PCH	MODE B	PB	PCL
1	0   0	0	X	0	0	X

= 80 H

I designed a table to show you the data bytes to be sent for specific combinations

For port B output

To glow	PA7	PA6	PA5	PA4	PA3	PA2	PA1	PA0	Port A output
R1,R2,G3 AND G4	X	X	0	0	1	0	0	1	0H
Y1, Y2, Y3 AND Y4	X	X	0	1	0	0	1	0	12H
R3,R4,G1 AND G2	X	X	1	0	0	1	0	0	24H

Source program for Traffic Light Control Using Microprocessor 8255

MVI A,80H --------------------initialize 8255, port A and port B
OUT 83H(CR)-----------------in output mode
START : MVI A, 09H
OUT 80H (PA)----------------send data on PA to glow R1 and R2
MVI A,24H
OUT 81H (PB)----------------send data on PB to glow G3 and G4
MVI C,28H--------------------Load multiplier count (40 10) for delay
CALL DELAY----------------Call delay subroutine
MVI A, 12H
OUT (81H) PA----------------send data on port A to glow Y1 and Y2
OUT (81H) PB----------------Send data on port B to glow Y3 and Y4
MVI C, 0AH-------------------Load multiplier count (10 10) for delay
CALL DELAY----------------call delay subroutine
MVI A, 24H
OUT (80H) PA----------------Send data on port A to glow G1 and G2
MVI A, 09H
OUT (81H) PB--------------send data on port B to glow R3 and R4
MVI C, 28H----------------- Load multiplier count (40 10) for delay
CALL DELAY-------------- call delay subroutine
MVI A, 12H
OUT PA---------------------- send data on port A to glow Y1 and Y2
OUT PB---------------------- Send data on port B to glow Y3 and Y4
MVI C, 0AH----------------- Load multiplier count (10 10) for delay
CALL DELAY-------------- call delay subroutine

JMP START

Delay Subroutine:

DELAY: LXI D, Count -----------Load count to give 0.5 sec delay.
BACK : DCX D --------------------------Decrement counter
MOV A,D
ORA E----------------------------------check whether count is 0
JNZ BACK ----------------------------if not zero, repeat
DCR C --------------------------------- check if multiplier zero, oherwise repeat
JNZ DELAY
RET ------------------------ return to main program.