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Traffic Contr oller

N.R. Paranjape

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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