TRAFFIC CONTROLLER                                                                         This simple traffic controller can
be used to teach children rudiments
of traffic rules.
The circuit (shown in Fig. 1) uses
readily available components. It mainly
comprises rectifier diodes (1N4001),
a 5V regulator 7805, two timers IC 555,
two relays (5V, single-changeover),
three 15W, 230V bulbs and some discrete
components.
Mains power is stepped down by
transformer X1 to deliver a secondary
output of 9V, 300 mA. The transformer
output is rectified by a full-wave
bridge rectifier comprising diodes D1
through D4, filtered by capacitor C1
and regulated by IC 7805 (IC1).
IC2 is wired as a multivibrator with
‘on’ and ‘off’ periods of approximately
30 seconds each with the component
values selected. As soon as mains
power is switched on, pin 3 of IC2 goes
high for 30 seconds. This, in turn, energises
relay RL1 through transistor T1
and the red lamp (B1) glows through
its normally-open (N/O) contact. At
the same time, mains power is disconnected
from the pole of relay RL2.
As the ‘on’ time of IC2 ends, a
Fig. 1: Circuit of traffic controller
Fig. 2: Construction details of traffic controller unit
high-to-low pulse at its pin 3
triggers IC3 through C5. IC3
is configured as a monostable
with ‘on’ time of about 4
seconds, which means pin 3
of IC3 will remain high for
this period and energise relay
RL2 through driver transistor
T2. The amber lamp (B2) thus
lights up for 4 seconds.
As soon as 4-second time
period of timer IC3 at pin 3
lapses, relay RL2 de-energises
and the green lamp (B3)
lights up for the rest of ‘off’
period of IC2, which is about
26 seconds. The green lamp
is activated through the normally
closed (N/C) contacts
of relay RL2.
So when mains power is
switched on, red light glows for
30 seconds, amber for 4 seconds
and green for 26 seconds.
You can assemble this circuit
on a general-purpose PCB
and enclose in an insulated
box. The box should have
enough space for mounting
transformer X1 and two relays.

It can be fixed near 230V
circuit
ideas
electronics for you • w w w. e f y m a g . c o m November 2008 • 81
AC, 50Hz power supply or mounted
on the PVC tube used in construction
of the traffic light container.
Construction of the traffic light
container box is shown in Fig. 2. A
stout cardboard box of 30x15x10cm3 is
required for housing the lamps. To ensure
strength, use a 10x45cm2 plywood
plate having 1.5cm thickness and secure
onto it three light sockets and the
box using nuts and bolts or screws.
Make three tubes of thin aluminium
sheet, which is readily available in
hardware shops. The inner diameter of
aluminium tubes should be such that
these can snugly fit on the light sockets.
Using a sharp knife, make holes
opposite the sockets carefully. Wire the
sockets at the back and take the wires
out through the PVC tube.
First, fix three 15W bulbs (B1
through B3) and then press on the
tubes. Support the other ends of the
tubes in the holes made on the front
panel of cardboard box. Sandwich gelatine
papers of the three colours between
two sheets of cardboard and fix over the
tubes. The visibility of red, amber and
green lights improves with their mounting
on the tubulaThis simple traffic controller can
be used to teach children rudiments
of traffic rules.
The circuit (shown in Fig. 1) uses
readily available components. It mainly
comprises rectifier diodes (1N4001),
a 5V regulator 7805, two timers IC 555,
two relays (5V, single-changeover),
three 15W, 230V bulbs and some discrete
components.
Mains power is stepped down by
transformer X1 to deliver a secondary    
output of 9V, 300 mA. The transformer
output is rectified by a full-wave
bridge rectifier comprising diodes D1
through D4, filtered by capacitor C1
and regulated by IC 7805 (IC1).
IC2 is wired as a multivibrator with
‘on’ and ‘off’ periods of approximately
30 seconds each with the component
values selected. As soon as mains
power is switched on, pin 3 of IC2 goes
high for 30 seconds. This, in turn, energises
relay RL1 through transistor T1
and the red lamp (B1) glows through
its normally-open (N/O) contact. At
the same time, mains power is disconnected
from the pole of relay RL2.
As the ‘on’ time of IC2 ends, a
Fig. 1: Circuit of traffic controller
Fig. 2: Construction details of traffic controller unit
high-to-low pulse at its pin 3
triggers IC3 through C5. IC3
is configured as a monostable
with ‘on’ time of about 4
seconds, which means pin 3
of IC3 will remain high for
this period and energise relay
RL2 through driver transistor
T2. The amber lamp (B2) thus
lights up for 4 seconds.
As soon as 4-second time
period of timer IC3 at pin 3
lapses, relay RL2 de-energises
and the green lamp (B3)
lights up for the rest of ‘off’
period of IC2, which is about
26 seconds. The green lamp
is activated through the normally
closed (N/C) contacts
of relay RL2.
So when mains power is
switched on, red light glows for
30 seconds, amber for 4 seconds
and green for 26 seconds.
You can assemble this circuit
on a general-purpose PCB
and enclose in an insulated
box. The box should have
enough space for mounting
transformer X1 and two relays.
It can be fixed near 230V
circuit
ideas
electronics for you • w w w. e f y m a g . c o m November 2008 • 81
AC, 50Hz power supply or mounted
on the PVC tube used in construction
of the traffic light container.
Construction of the traffic light
container box is shown in Fig. 2. A
stout cardboard box of 30x15x10cm3 is
required for housing the lamps. To ensure
strength, use a 10x45cm2 plywood
plate having 1.5cm thickness and secure
onto it three light sockets and the
box using nuts and bolts or screws.
Make three tubes of thin aluminium
sheet, which is readily available in
hardware shops. The inner diameter of
aluminium tubes should be such that
these can snugly fit on the light sockets.
Using a sharp knife, make holes
opposite the sockets carefully. Wire the
sockets at the back and take the wires
out through the PVC tube.
First, fix three 15W bulbs (B1
through B3) and then press on the
tubes. Support the other ends of the
tubes in the holes made on the front
panel of cardboard box. Sandwich gelatine
papers of the three colours between
two sheets of cardboard and fix over the
tubes. The visibility of red, amber and
green lights improves with their mounting
on the tubula