Automatic traffic signal controller
C I R C U I T I D E A S
NOVEMBER 2002 ELECTRONICS FOR YOU
RUPANJANA
AUTOMATED TRAFFIC SIGNAL
CONTROLLER
This automated traffic signal controller
can be made by suitably programming
a GAL device. (For GAL
programming you may refer to the construction
project published on page 52 in
EFY’s September issue.) Its main features
are:
1. The controller assumes equal traffic
density on all the roads.
2. In most automated traffic signals the
free left-turn condition is provided throughout
the entire signal period, which poses
difficulties to the pedestrians in crossing
the road, especially when the traffic den-
VIKRAM BANERJEE
MRINAL KANTI MANDAL
DR ANIRUDHA GHOSAL
sity is high. This controller allows the pedestrians
to safely cross the road during
certain periods.
3. The controller uses digital logic,
which can be easily implemented by using
logic gates.
4. The controller is a generalised one
and can be used for different roads with
slight modification.
5. The control can also be exercised
manually when desired.
The time period for which green, yellow,
and red traffic signals remain ‘on’
(and then repeat) for the straight moving
traffic is divided into eight units of 8
seconds (or multiples thereof) each. Fig.
1 shows the flow of traffic in all permissible
directions during the eight time units
of 8 seconds each. For the left- and rightturning
traffic and pedestrians crossing
from north to south, south to north, east
to west, and west to east, only green and
red signals are used.
Table I shows the simultaneous states
of the signals for all the traffic. Each row
represents the status of a signal for 8
seconds. As can be observed from the
table, the ratio of green, yellow, and red
signals is 16:8:40 (=2:1:5) for the straight
moving traffic. For the turning traffic the
ratio of green and red signals is 8:56
(=1:7), while for pedestrians crossing the
road the ratio of green and red signals is
16:48 (=2:6).
In Table II (as well as Table I) X, Y,
and Z are used as binary variables to
Fig. 1: Flow of traffic in all possible directions
TABLE I
Simultaneous States of Signals for All the Traffic
X Y Z B-C/B-G B-E D-E/D-A D-G F-G/F-C F-A H-A/H-E HC WALK WALK
Lt/Rt St Lt/Rt St Lt/Rt St Lt/Rt St (N-S)/(S-N) (E-W)/(W-E)
0 0 0 R R R R G G R R R R
0 0 1 R G R R R G R R G R
0 1 0 R G R R R Y R R G R
0 1 1 G Y R R R R R R R R
1 0 0 R R R R R R G G R R
1 0 1 R R R G R R R G R G
1 1 0 R R R G R R R Y R G
1 1 1 R R G Y R R R R R R
C I R C U I T I D E A S
ELECTRONICS FOR YOU NOVEMBER 2002
depict the eight states of 8
seconds each. Letters A
through H indicate the left
and right halves of the roads
in four directions as shown
in Fig. 1. Two letters with a
dash in between indicate the
direction of permissible
movement from a road.
Straight direction is indicated
by St, while left and right
turns are indicated by Lt and
Rt, respectively.
The Boolean functions
for all the signal conditions
are shown in Table II.
The left- and the right-turn
signals for the traffic have
the same state, i.e. both are
red or green for the same
duration, so their Boolean
functions are identical and
they should be
connected to the same con-
Fig. 2: The circuit diagram for traffic light signalling
TABLE II
Boolean Functions for All the Signal Conditions
Signal Reference Boolean functions
Green B-C(Lt)/B-G (Rt) X’YZ
Green B-E (St) XYZ’+X’Y’Z
Red B-E (St) X+Y’Y’Z’
Yellow B-E (St) X’YZ
Green D-E (Lt)/D-A (Rt) XYZ
Green D-G (St) XYZ’+XY’Z
Red D-G (St) X’+XY’Z’
Yellow D-G (St) XYZ
Green F-G(Lt)/F-C (Rt) X’Y’Z’
Green F-A (St) X’Y’
Red F-A (St) X+X’YZ
Yellow F-A (St) X’YZ’
Green H-A (Lt)/H-E (Rt) XY’Z’
Green H-C (St) XY’
Red H-C (St) X’+XYZ
Yellow H-C (St) XYZ’
Green Walk (N-S/S-N) X’YZ’+X’Y’Z
Green Walk (E-W/W-E) XYZ’+XY’Z
Note. X’, Y’, and Z’ denote complements of variables X, Y,
and Z, respectively.
trol output.
The circuit diagram for realising these
Boolean functions is shown in Fig. 2.
Timer 555 (IC1) is wired as an astable
multivibrator to generate clock signal for
the 4-bit counter 74160 (IC2). The time
duration of IC1 can be adjusted by varying
the value of resistor R1, resistor R2,
or capacitor C2 of the clock circuit. The
‘on’ time duration T is given by the following
relationship:
T = 0.695C2(R1+R2)
IC2 is wired as a 3-bit binary counter
by connecting its Q3 output to reset pin 1
via inverter N1. Binary outputs Q2, Q1,
and Q0 form variables X, Y, and Z, respectively.
These outputs, along with their
complimentary outputs X’, Y’, and Z’,
respectively, are used as inputs to the rest
of the logic circuit to realise various outputs
satisfying Table I.
You can simulate various traffic lights
using green, yellow, and red LEDs and
feed the outputs of the circuit to respective
LEDs via
current-limiting
resistors of
470 ohms each
to check the
working of the
circuit. Here,
for turning traffic
and pedestrians
crossing
the road, only
green signal is
made available.
It means
that for the remaining
period
these signals
have to be
treated as ‘red’.
In practice,
the outputs of
Fig. 2 should
be connected
to solidstate relays
to operate
h i g h - p o w e r
bulbs. Further,
if a particular
signal condition
(such as
turning signal)
is not applicable
to a
given road, the
output of that
signal condition
should be
C I R C U I T I D E A S
NOVEMBER 2002 ELECTRONICS FOR YOU
#include<stdio.h>
#include<conio.h>
#define TRUE 1
#define False 0
int not(int x);
int or2(int x,int y);
int or3(int x,int y,int z);
int and2(int x,int y);
int and3(int x,int y,int z);
int main(void)
{
int a,b,c;
int seq,green_bl,green_bs,red_bs,yellow_bs;
int green_dl,green_ds,red_ds,yellow_ds;
int green_fl,green_fs,red_fs,yellow_fs;
int green_hl,green_hs,red_hs,yellow_hs;
int walk_ns,stop_ns;
int walk_ew,stop_ew;
clrscr();
printf(“ SIG-B SIG-D SIF-F SIG-H
WALK(N-S) WALK(E-W)\n”);
printf(“G G R Y G G R Y G G R Y G G R Y
G R G R\n”);
for(seq=0;seq<8;seq++)
{
c=(seq&1);b=(seq&2)>>1;a=(seq&4)>>2;
green_bl=and3(not(a),b,c);
green_bs=or2(and3(not(a),b,not(c)),and3(not(a),not(b),c));
red_bs=or2(a,and3(not(a),not(b),not(c)));
yellow_bs=and3(not(a),b,c);
green_dl=and3(a,b,c);
green_ds=or2(and3(a,b,not(c)),and3(a,not(b),c));
red_ds=or2(not(a),and3(a,not(b),not(c)));
yellow_ds=and3(a,b,c);
green_fl=and3(not(a),not(b),not(c));
green_fs=and2(not(a),not(b));
red_fs=or2(a,and3(not(a),b,c));
yellow_fs=and3(not(a),b,not(c));
green_hl=and3(a,not(b),not(c));
green_hs=and2(a,not(b));
red_hs=or2(not(a),and3(a,b,c));
yellow_hs=and3(a,b,not(c));
walk_ns=green_bs;
stop_ns=or3(and3(not(a),not(b),not(c)),and3(not(a),b,c),a);
walk_ew=green_ds;
stop_ew=or3(not(a),and3(a,b,c),and3(a,not(b),not(c)));
printf(“%d %d %d %d %d %d %d %d
%d %d %d %d %d %d %d %d %d %d
%d %d\n”,
green_bl,green_bs,red_bs,yellow_bs,
green_dl,green_ds,red_ds,yellow_ds,
green_fl,green_fs,red_fs,yellow_fs,
green_hl,green_hs,red_hs,yellow_hs,
walk_ns,stop_ns,
walk_ew,stop_ew);
getch();
}
return;
}
int and2(int x,int y)
{
return(x && y);
}
int and3(int x,int y,int z)
{
return(x && y && z);
}
int or2(int x,int y)
{
return(x || y);
}
int or3(int x,int y,int z)
{
return(x || y || z);
}
int not(int x)
{
return(!x);
}
TRAFFIC.C
Table III
Execution Results of Software Program
SIG-B SIG-D SIF-F SIG-H WALK(N-S) WALK(E-W)
G G R Y G G R Y G G R Y G G R Y G R G R
0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1 0 1
0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0 1
0 1 0 0 0 1 0 0 0 0 0 1 0 0 1 0 1 0 0 1
1 0 0 1 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1
0 0 1 0 0 1 0 0 0 0 1 0 1 1 0 0 0 1 0 1
0 0 1 0 1 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0
0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 1 0 1 1 0
0 0 1 0 0 0 1 1 0 0 1 0 0 0 1 0 0 1 0 1
Note. The first column under G (green) in each group of four signals indicates the
turn signal, while the next three columns under GRY indicate signal for the straight
traffic.
connected
to green
signal of
the next
state (refer
Table I).
T h e
traffic signals
can
also be
controlled
manually,
if desired.
Any signal
state can be
established
by entering the binary value corresponding
to that particular state into the parallel
input pins of the 3-bit counter. Similarly,
the signal can be reset at any time by
providing logic 0 at the reset pin (pin 1)
of the counter using an external switch.
A software program to verify the
functioning of the circuit using a PC
is given below. (Source code and executable
file will be provided in the next
month’s EFY-CD.) When executing the program,
keep pressing Enter key to get the
next row of results. The test results on
execution of the program is shown in Table
III.
NOVEMBER 2002 ELECTRONICS FOR YOU
RUPANJANA
AUTOMATED TRAFFIC SIGNAL
CONTROLLER
This automated traffic signal controller
can be made by suitably programming
a GAL device. (For GAL
programming you may refer to the construction
project published on page 52 in
EFY’s September issue.) Its main features
are:
1. The controller assumes equal traffic
density on all the roads.
2. In most automated traffic signals the
free left-turn condition is provided throughout
the entire signal period, which poses
difficulties to the pedestrians in crossing
the road, especially when the traffic den-
VIKRAM BANERJEE
MRINAL KANTI MANDAL
DR ANIRUDHA GHOSAL
sity is high. This controller allows the pedestrians
to safely cross the road during
certain periods.
3. The controller uses digital logic,
which can be easily implemented by using
logic gates.
4. The controller is a generalised one
and can be used for different roads with
slight modification.
5. The control can also be exercised
manually when desired.
The time period for which green, yellow,
and red traffic signals remain ‘on’
(and then repeat) for the straight moving
traffic is divided into eight units of 8
seconds (or multiples thereof) each. Fig.
1 shows the flow of traffic in all permissible
directions during the eight time units
of 8 seconds each. For the left- and rightturning
traffic and pedestrians crossing
from north to south, south to north, east
to west, and west to east, only green and
red signals are used.
Table I shows the simultaneous states
of the signals for all the traffic. Each row
represents the status of a signal for 8
seconds. As can be observed from the
table, the ratio of green, yellow, and red
signals is 16:8:40 (=2:1:5) for the straight
moving traffic. For the turning traffic the
ratio of green and red signals is 8:56
(=1:7), while for pedestrians crossing the
road the ratio of green and red signals is
16:48 (=2:6).
In Table II (as well as Table I) X, Y,
and Z are used as binary variables to
Fig. 1: Flow of traffic in all possible directions
TABLE I
Simultaneous States of Signals for All the Traffic
X Y Z B-C/B-G B-E D-E/D-A D-G F-G/F-C F-A H-A/H-E HC WALK WALK
Lt/Rt St Lt/Rt St Lt/Rt St Lt/Rt St (N-S)/(S-N) (E-W)/(W-E)
0 0 0 R R R R G G R R R R
0 0 1 R G R R R G R R G R
0 1 0 R G R R R Y R R G R
0 1 1 G Y R R R R R R R R
1 0 0 R R R R R R G G R R
1 0 1 R R R G R R R G R G
1 1 0 R R R G R R R Y R G
1 1 1 R R G Y R R R R R R
C I R C U I T I D E A S
ELECTRONICS FOR YOU NOVEMBER 2002
depict the eight states of 8
seconds each. Letters A
through H indicate the left
and right halves of the roads
in four directions as shown
in Fig. 1. Two letters with a
dash in between indicate the
direction of permissible
movement from a road.
Straight direction is indicated
by St, while left and right
turns are indicated by Lt and
Rt, respectively.
The Boolean functions
for all the signal conditions
are shown in Table II.
The left- and the right-turn
signals for the traffic have
the same state, i.e. both are
red or green for the same
duration, so their Boolean
functions are identical and
they should be
connected to the same con-
Fig. 2: The circuit diagram for traffic light signalling
TABLE II
Boolean Functions for All the Signal Conditions
Signal Reference Boolean functions
Green B-C(Lt)/B-G (Rt) X’YZ
Green B-E (St) XYZ’+X’Y’Z
Red B-E (St) X+Y’Y’Z’
Yellow B-E (St) X’YZ
Green D-E (Lt)/D-A (Rt) XYZ
Green D-G (St) XYZ’+XY’Z
Red D-G (St) X’+XY’Z’
Yellow D-G (St) XYZ
Green F-G(Lt)/F-C (Rt) X’Y’Z’
Green F-A (St) X’Y’
Red F-A (St) X+X’YZ
Yellow F-A (St) X’YZ’
Green H-A (Lt)/H-E (Rt) XY’Z’
Green H-C (St) XY’
Red H-C (St) X’+XYZ
Yellow H-C (St) XYZ’
Green Walk (N-S/S-N) X’YZ’+X’Y’Z
Green Walk (E-W/W-E) XYZ’+XY’Z
Note. X’, Y’, and Z’ denote complements of variables X, Y,
and Z, respectively.
trol output.
The circuit diagram for realising these
Boolean functions is shown in Fig. 2.
Timer 555 (IC1) is wired as an astable
multivibrator to generate clock signal for
the 4-bit counter 74160 (IC2). The time
duration of IC1 can be adjusted by varying
the value of resistor R1, resistor R2,
or capacitor C2 of the clock circuit. The
‘on’ time duration T is given by the following
relationship:
T = 0.695C2(R1+R2)
IC2 is wired as a 3-bit binary counter
by connecting its Q3 output to reset pin 1
via inverter N1. Binary outputs Q2, Q1,
and Q0 form variables X, Y, and Z, respectively.
These outputs, along with their
complimentary outputs X’, Y’, and Z’,
respectively, are used as inputs to the rest
of the logic circuit to realise various outputs
satisfying Table I.
You can simulate various traffic lights
using green, yellow, and red LEDs and
feed the outputs of the circuit to respective
LEDs via
current-limiting
resistors of
470 ohms each
to check the
working of the
circuit. Here,
for turning traffic
and pedestrians
crossing
the road, only
green signal is
made available.
It means
that for the remaining
period
these signals
have to be
treated as ‘red’.
In practice,
the outputs of
Fig. 2 should
be connected
to solidstate relays
to operate
h i g h - p o w e r
bulbs. Further,
if a particular
signal condition
(such as
turning signal)
is not applicable
to a
given road, the
output of that
signal condition
should be
C I R C U I T I D E A S
NOVEMBER 2002 ELECTRONICS FOR YOU
#include<stdio.h>
#include<conio.h>
#define TRUE 1
#define False 0
int not(int x);
int or2(int x,int y);
int or3(int x,int y,int z);
int and2(int x,int y);
int and3(int x,int y,int z);
int main(void)
{
int a,b,c;
int seq,green_bl,green_bs,red_bs,yellow_bs;
int green_dl,green_ds,red_ds,yellow_ds;
int green_fl,green_fs,red_fs,yellow_fs;
int green_hl,green_hs,red_hs,yellow_hs;
int walk_ns,stop_ns;
int walk_ew,stop_ew;
clrscr();
printf(“ SIG-B SIG-D SIF-F SIG-H
WALK(N-S) WALK(E-W)\n”);
printf(“G G R Y G G R Y G G R Y G G R Y
G R G R\n”);
for(seq=0;seq<8;seq++)
{
c=(seq&1);b=(seq&2)>>1;a=(seq&4)>>2;
green_bl=and3(not(a),b,c);
green_bs=or2(and3(not(a),b,not(c)),and3(not(a),not(b),c));
red_bs=or2(a,and3(not(a),not(b),not(c)));
yellow_bs=and3(not(a),b,c);
green_dl=and3(a,b,c);
green_ds=or2(and3(a,b,not(c)),and3(a,not(b),c));
red_ds=or2(not(a),and3(a,not(b),not(c)));
yellow_ds=and3(a,b,c);
green_fl=and3(not(a),not(b),not(c));
green_fs=and2(not(a),not(b));
red_fs=or2(a,and3(not(a),b,c));
yellow_fs=and3(not(a),b,not(c));
green_hl=and3(a,not(b),not(c));
green_hs=and2(a,not(b));
red_hs=or2(not(a),and3(a,b,c));
yellow_hs=and3(a,b,not(c));
walk_ns=green_bs;
stop_ns=or3(and3(not(a),not(b),not(c)),and3(not(a),b,c),a);
walk_ew=green_ds;
stop_ew=or3(not(a),and3(a,b,c),and3(a,not(b),not(c)));
printf(“%d %d %d %d %d %d %d %d
%d %d %d %d %d %d %d %d %d %d
%d %d\n”,
green_bl,green_bs,red_bs,yellow_bs,
green_dl,green_ds,red_ds,yellow_ds,
green_fl,green_fs,red_fs,yellow_fs,
green_hl,green_hs,red_hs,yellow_hs,
walk_ns,stop_ns,
walk_ew,stop_ew);
getch();
}
return;
}
int and2(int x,int y)
{
return(x && y);
}
int and3(int x,int y,int z)
{
return(x && y && z);
}
int or2(int x,int y)
{
return(x || y);
}
int or3(int x,int y,int z)
{
return(x || y || z);
}
int not(int x)
{
return(!x);
}
TRAFFIC.C
Table III
Execution Results of Software Program
SIG-B SIG-D SIF-F SIG-H WALK(N-S) WALK(E-W)
G G R Y G G R Y G G R Y G G R Y G R G R
0 0 1 0 0 1 0 0 1 1 0 0 0 0 1 0 0 1 0 1
0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 0 1 0 0 1
0 1 0 0 0 1 0 0 0 0 0 1 0 0 1 0 1 0 0 1
1 0 0 1 0 1 0 0 0 0 1 0 0 0 1 0 0 1 0 1
0 0 1 0 0 1 0 0 0 0 1 0 1 1 0 0 0 1 0 1
0 0 1 0 1 0 0 0 0 0 1 0 0 1 0 0 0 1 1 0
0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 1 0 1 1 0
0 0 1 0 0 0 1 1 0 0 1 0 0 0 1 0 0 1 0 1
Note. The first column under G (green) in each group of four signals indicates the
turn signal, while the next three columns under GRY indicate signal for the straight
traffic.
connected
to green
signal of
the next
state (refer
Table I).
T h e
traffic signals
can
also be
controlled
manually,
if desired.
Any signal
state can be
established
by entering the binary value corresponding
to that particular state into the parallel
input pins of the 3-bit counter. Similarly,
the signal can be reset at any time by
providing logic 0 at the reset pin (pin 1)
of the counter using an external switch.
A software program to verify the
functioning of the circuit using a PC
is given below. (Source code and executable
file will be provided in the next
month’s EFY-CD.) When executing the program,
keep pressing Enter key to get the
next row of results. The test results on
execution of the program is shown in Table
III.
Download Ppt in a Single File
