Natwerk Designs

how to make a four way traffic controlled system?

I am the student of ELECTRONIC ENGG in third semester.I am making four way traffic controlled system , how can i control the timing for which a particular light (one of Red,Green or Yellow) will be on i.e. glow. say i want that green and light LEDs should glow for 6 seconds each and yellow for three seconds. LM555 is on of the option but don't know much about using that so i want some easy alternative, which may be I can design myself. Or if someone know where can i find this system on net.

Public Comments

1. Traffic light system? Well, in my opinion the easiest way would be to use a microcontroller. Hardware would remain constant. Any changes in timing, sequence of lights, etc. would be effected in firmware.
2. You're describing a state machine, which you *could* do using D Flip-Flops and combinational logic (NAND's, NOR's, etc.). I'd recommend a 555 as your base timer, then use the clock signal generated from it to drive the state changes for the rest of your logic circuitry. A microprocessor is almost certainly beyond your expertise at this point if you feel uncomfortable with a 555. The 555 and the 741 Op-Amp are such basic building blocks for most circuits that I'd strongly recommend you get comfortable with them now. That knowledge will serve you well in the future.
3. I'll second the micro controller recomendation, you can also use a plc ... I would consider running either as a state machine where 12 lights (Red, Yello, Green) are represented in bit patterns as to there on/off state. 12 lights = 4 directions x 3 lights So you will have sequences of bit patterns in memory and you step through each pattern one at a time in a defined time period. This is an electronic version of a cam timer like what you would find on a washer machine. for example 3 bits for three lights RYG 100 red is lit 001 green is lit 010 yellow is lit loop back to start in this example you have three states and each step is used for the same amount of time. To extend the duration of a given light display you merely repeat the bit pattern by adding a copy to the sequence. Below the green light display is extended start: 100 red is lit 001 green is lit 001 green is lit 010 yellow is lit loop back to start