ladder help please

Ok Im sure Im going to to get ripped for this. But i need help with writing the logic for a single traffic light. I did this a few years back with timers in school but i can't for the life of me make it on the computer. I have no pic training and Im sure Im going to get knocked for that....Im learning as i go i won't be programming for anyone but my self. Im not asking for you to do the work for me if you could tell me what timers i need and how many that would be great. Thanks for any help you can provide.

Look in the downloads section of the forum.

http://www.plcs.net/downloads/index...ey&PHPSESSID=28d3d248829adf09a716daa403c2ed62

tatersalad said:

... if you could tell me what timers i need and how many that would be great. Thanks for any help you can provide.

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In real life, nobody tells us how many timers are needed on a real project.

The most important part of any automation project is to define what you want it to do. Fortunately, a stop light is pretty well known - we all know the sequence, etc... Write it down - put it in a flow chart - somehow document your process.

Then think about how your system will know to step from one state to the next - will it be based on time or on an action or what?

That information will lead you to know how many timers you'll need.

FWIW, it can be done with some careful manipulation of as few as 1, yes one, timer. But, I always have to ask, is that really the right, most efficient way?

Alaric-thank you that was just what I needed
Ozee-I understand that, in school I want to say we used 4 timers but I just made it with 3 I was having a hard time trying to figure out how to make it recycle. I figured it out not used to the plc terms.... I can wire most anything else with out a problem.

BTW, If this is a homework assignment then don't just copy that and turn it in. Chances are your instructor knows about this place.

Nope just wanted to make my street light function

OZEE said:

FWIW, it can be done with some careful manipulation of as few as 1, yes one, timer. But, I always have to ask, is that really the right, most efficient way?

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Depending on what controller you use, a simple 4-way crossing traffic-light sequence can be done without using any timers at all, and using only 2 instructions in the code.

It certainly is the most efficient (in code terms), but not necessarily the right way, as it is relatively difficult to modify.

Having said that, when was the last time you saw your local traffic lights modified? In my locale, I can think of several traffic lights that are programmed wrongly, resulting in poor traffic flow.

My favourite is a four-way intersection 2 miles away that only has green lights from each of the four "entrances" at any one time, and although left-turn filter lights are installed (UK, we drive on the left), they are not programmed with any intelligence, and are not used at all. That's dumb.

And why do traffic lights change 24/7 when there is no need to change? They all have vehicle approaching sensors, and could easily be programmed to give a green light to approaching traffic at quiet times of the day. 200 yards from where I live is a set of lights that can stop you as you approach, and no traffic comes from the other directions, it just goes through its timed sequence at all times. That's dumb also

sorry, just grabbed an opportunity to have a whinge....

yes one, timer. But, I always have to ask, is that really the right,

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using the acc of just one timer and comparitve instructions is far better IMO