I have given the assignment to draw conventional ladder diagram for three bulbs which give light alternatively at equal intervals (using time delay contactors)
the number of timers used must be as minimum as possible.
my difficulty is on mannaging contactors(time contactors)-please help me.

 

We need at least some details about what you have managed to do - http://forum.allaboutcircuits.com/showthread.php?t=3002.

We are here to give assistance, not do the project for you.

 

http://www.eod.gvsu.edu/~jackh/books/plcs/

 

The problem is connecting the contactors. when i try to connect to contactors parallel with their normal closed and openend contacts the lights glow simeltaneously. but what i want is the lamps should give light alternatively in a regular constant time interval.
in my trial there is a STOP at first place and START next to that parallel to this START there is contact(conventional contact) which is normally oppened. this contact needs enrgization of the contactor that is placed at last parallely to the timers and lamps to be closed. And i have connected the time delayed contactors and lamps in parallel.

 

You can use a timer and a 4 bit counter to simulate a traffic light. The counter has 16 states, 0000 - 1111. You can set up how long you want the red, yellow, and green to be on. If you want red to be on for 4 clock cycles, whenever you have 0000,0001,0010,0011 you want red to be on. So for every counter state (0000-1111) one of the lights will be on. Draw a truth table with the counter states (Q1,Q2,Q3,Q4) and the 3 lights, R, Y, G. Determine which light will be logic 1 for each state. Use K-Maps to derive the flip flop equations.

 

Nice! thankyou!