1. circuit
ideas
Traffic Controller s.c. dwiv
edi
 N.R. Paranjape high-to-low pulse at its pin 3
triggers IC3 through C5. IC3
T
his simple traffic controller can is configured as a monosta-
be used to teach children rudi- ble with ‘on’ time of about 4
ments of traffic rules. seconds, which means pin 3
The circuit (shown in Fig. 1) uses of IC3 will remain high for
readily available components. It main- this period and energise relay
ly comprises rectifier diodes (1N4001), RL2 through driver transistor
a 5V regulator 7805, two timers IC 555, T2. The amber lamp (B2) thus
two relays (5V, single-changeover), lights up for 4 seconds.
three 15W, 230V bulbs and some dis- As soon as 4-second time
crete components. period of timer IC3 at pin 3
Mains power is stepped down by lapses, relay RL2 de-ener-
transformer X1 to deliver a secondary gises and the green lamp (B3)
output of 9V, 300 mA. The transformer lights up for the rest of ‘off’
output is rectified by a full-wave period of IC2, which is about
bridge rectifier comprising diodes D1 26 seconds. The green lamp
through D4, filtered by capacitor C1 is activated through the nor-
and regulated by IC 7805 (IC1). mally closed (N/C) contacts
IC2 is wired as a multivibrator with of relay RL2.
‘on’ and ‘off’ periods of approximately So when mains power is
30 seconds each with the component switched on, red light glows for
values selected. As soon as mains 30 seconds, amber for 4 seconds
power is switched on, pin 3 of IC2 goes and green for 26 seconds.
high for 30 seconds. This, in turn, ener- You can assemble this cir-
gises relay RL1 through transistor T1 cuit on a general-purpose PCB
and the red lamp (B1) glows through and enclose in an insulated
its normally-open (N/O) contact. At box. The box should have
the same time, mains power is discon- enough space for mounting
nected from the pole of relay RL2. transformer X1 and two re-
As the ‘on’ time of IC2 ends, a lays. It can be fixed near 230V Fig. 2: Construction details of traffic controller unit
Fig. 1: Circuit of traffic controller
8 0 • N o v e m b e r 2 0 0 8 • e l e c t ro n i c s f o r yo u w w w. e f y m ag . co m

2. circuit
ideas
AC, 50Hz power supply or mounted box using nuts and bolts or screws. First, fix three 15W bulbs (B1
on the PVC tube used in construction Make three tubes of thin alumini- through B3) and then press on the
of the traffic light container. um sheet, which is readily available in tubes. Support the other ends of the
Construction of the traffic light hardware shops. The inner diameter of tubes in the holes made on the front
container box is shown in Fig. 2. A aluminium tubes should be such that panel of cardboard box. Sandwich gela-
stout cardboard box of 30x15x10cm3 is these can snugly fit on the light sock- tine papers of the three colours between
required for housing the lamps. To en- ets. Using a sharp knife, make holes two sheets of cardboard and fix over the
sure strength, use a 10x45cm2 plywood opposite the sockets carefully. Wire the tubes. The visibility of red, amber and
plate having 1.5cm thickness and se- sockets at the back and take the wires green lights improves with their mount-
cure onto it three light sockets and the out through the PVC tube. ing on the tubular shape. 
w w w. e f y m ag . co m e l e c t ro n i c s f o r yo u • N o v e m b e r 2 0 0 8 • 8 1