Traffic Light Controller

Posted on Feb 6, 2014

Here the simple traffic light controller which is could be used to educate kids rudiments of traffic light guidelines. The circuit utilizes easily available electronic parts. It generally consists of rectifier diodes (1N4001), a 5V regulator 7805, two timers circuit using IC 555, two relays (5V, single-changeover), three 15W, 230V light bulbs and

Traffic Light Controller
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also several discrete parts. Mains electrical power is stepped down by transformer X1 to provide a secondary output voltage of 9V, 300 mA AC. Then the transformer output current is rectified by a full-wave bridge rectifier composed of diodes D1 through D4, filtered by capacitor C1 and also regulated by IC 7805 (IC1). IC2 is wired as a multivibrator with on` and off` periods of about 30 seconds each with the part values determined. Once mains power switch is turned on, pin 3 of IC2 goes high for 30 seconds. This, in turn, energises relay RL1 via transistor T1 and the red bulb (B1) glows through its normally-open (N/O) contact. At the same time, mains power is turned off from the pole of relay RL2. As the on` time of IC2 ends, a triggers IC3 through C5. IC3 is set up as a monostable with on` time of about 4 seconds, which indicates pin 3 of IC3 will stay high for this period of time and energise relay RL2 through driver transistor T2. The amber bulb (B2) thus lightings up for 4 seconds. Immediately after 4-second time period of timer IC3 at pin 3 lapses, relay RL2 de-energises and also the green bulb (B3) lights up for the rest of off` period of IC2, which is about 26 seconds. The green bulb is turned on through the normally closed (N/C) contacts of relay RL2. So when mains electrical switch is turned on, red light will light up for 30 seconds, amber for 4 seconds and green for 26 seconds. You can easily build this circuit on...

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