Traffic light sequence, cross roads

[Eric Nelson]

Utoh... Here we go again!...

 

[Rick Densing]

Re: Engineer?

.
BY ASKING THE RIGHT PEOPLE THE RIGHT QUESTIONS AND LEARNING FROM THEM.

You asked the right people, I think.
You did not ask the right questions.
As you may have guessed, the traffic light question pops up every few months or so. Each time it sounds the same. You may not have realized it, but your question was interpreted as "I don't know how to do my assignment, please do it for me." This is not snobbery on our part. As stated in the introduction, how you ask is much more important that what you ask. If you had simply explained your efforts in more detail, you would have likely recieved a different response. Granted, the traffic light question is such a sore subject that you were handicapped from the start.

 

[Allen Nelson]

IMRAN:

You say you are having a problem with the traffic light code. What problem EXACTLY is the problem you are having.

Do you know what all your I/O are (6 lights minimum, but what about turn signals and crosswalks (aka zebra crossings)? Car detection pressure pads (how many?)?

Do you know the sequence? What are the transistions from each step to the next?

Or is there just some line of code tha you've writen, that .looks to your eyes like it should work, but for reasons you don't understand, it doesn;t.

Post what you don't understand, and we WILL{/b] give help. But we have no way of knowing where you are stuck, until you tell us. Don't chew us out for your shortcomings.

 

[Tom Jenkins]

OK, Imran, maybe we misjudged you. However, we can only go by our past experiences here (lots of lazy, sloppy students asking the IDENTICAL question) and by what you write in your post. Your original question was poorly defined and open ended.

Clearly defining the problem is the most critical step in obtaining a good solution.

 

[IMRAN]

Hello all.

I must appoligise with my last post. It was a little 'over done' by any standards. Sorry all I must sound like a real miserable wanker.

Also, Im sorry if the details were not made clear, I thought I had explained that it was simply a cross road, N-S and E-W, and that there was no plc to program just a computer simulator that works on ladder logic.

There was no way i would ask anyone to do my work for me. I just asked for assistance:
Rick, mate, read the question, dont assume what is being asked. Cheers!

But, with all that aside, i think i have cracked it now, just last night while on a tea break at work. I just need to test and debug now. So with that said, ill leave you all in peace!

Hopefully, (cos who knows where a job can take ya), i can come back here and call upon ur knowledge and experience in the future.
In a few years or so.

Take care.

 

[rsdoran]

Personally I dont think any apologies are needed by anyone, yes the traffic light thing comes up regularly...so what. Not all can see what needs to be done even when they may have done other things before. NO, noone should do anyone else's work but it doesnt hurt to give an idea/clue on a path to take...even if it is a student.

YES in most cases the students are lazy and looking for a freebie..so? In the real world they will act the same way so will NOT get the job/money etc they desire. WHY? Because they will not have learned HOW.

There was a time when YOU ALL didnt know the RIGHT question(s) to ask.

Not all students are kids looking for the easy route, some may just need a nudge in the right direction.

Yes I know this site gets deluged with that question every year..so what? WHERE else would they go for this kind of assistance? WHO else has this kind of knowledge? Ability?

You think most of them have an Instructor that is that capable?

You should be proud of the fact that you are the source of info for future minds.

To alleviate this deluge I have (besides Allen's post) 3 other traffic light ladder diagrams...from this day forward I plan to post them at the first sign of derision, not in response to the question.

 

[Tom Jenkins]

Thanks for posting back Imran. I'm glad you cracked it.

Hope to see you here some more.

 

[Matthias Von Zorn]

Well...

Then u need to ask the right questions. Do have any idea how many times we have seen "give me the answer to the traffic light! Need now!"?? If you want to avoid these rather generous peoples jabs, your should have posted differently. Why not tell us what you have done already, and where you are stuck? Obviously you care more than most (they almost never reply to our little games here). So if we mistook you, it was soley to the way you asked the question.

 

[Guest]

TRAFFIC LIGHTS

IMRAN, LIKE YOURSELF IAM TRYING TO HOLD DOWN 5&6 12 HOUR SHIFTS AS WELL AS STUDY A LIST OF SUBJECTS WHICH ARE COMPLETLY NEW TO ME IN THE HOPE THAT I MAY INPROVE ON MY FUTURE PROSPECTS.H.N.C ANY HELP YOU CAN OFFER ON THE LADDER DIAGRAM FOR THE LIGHTING SEQUENCE WOULD BE GREATLY APPREACHATY ................................IS THIS SITE NOT FOR THE SHARING OF KNOWLEDGE???????????????

 

[Allen Nelson]

Look at Post #2 - I put the soluton there. What more do you want?

Here, we don't just hand out code. We teach. Teaching involves effort on behalf of the student and the teacher.

This is our effort, where's yours?

 

[Rick Densing]

Re: TRAFFIC LIGHTS

Originally posted by
IAM TRYING TO HOLD DOWN 5&6 12 HOUR SHIFTS AS WELL AS STUDY A LIST OF SUBJECTS

And this somehow justifies having someone else do your work for you?
The logic escapes me.

 

[iant]

Well done Imran
However I have a question for you
I beleive the answer will benefit the 'students' who need to be given the answers.

Did you feel relieved and satisfied that you could crack the problem?

And what about the Logic skills you now have learnt doing this excercise..?

Please Post the Answer seperate to this thread.

As you know and others will learn 'we were not told by some one'
We learnt by teaching ourselves. and asking refined questions.
[how does .... operate] or [ how to input timer variables in a ... type PLC] etc.

Regards Ian T

 

[red alert cavy]

I still say stop signs would have saved the world A LOT of trouble. *sigh* I'm a beginning student and even I knew how to program those lights. Now I gotta figure out how to put a walk light in there.

 

[panic mode]

you can do one timer and bunch of LIM instructions (or GRT and LES)
to do this:

   T4:0/DN 

----|/|-------------------------------[T4:0]



                                      GREEN

---[LIM  N7:0 T4:0.ACC N7:1]-----------( )



                                       RED

---[LIM  N7:2 T4:0.ACC N7:3]-----------( )

etc.

 

[rms]

Thank you all

Just wanted to thank you all for a most interesting thread, albeit more from the sociology rather than a PLC angle. It was interesting to note that there was no discussion of what the UK traffic light sequence was and how the differences might affect the logic employed (I googled here while looking for other traffic light sequences than the UK and US models).

Obligatory traffic light humour/humor.

Traffic light sequence in UK.

Legal:
Red - Stop. Wait behind the stop line on the carriageway.
Red + Amber - Stop. Do not pass through until green shows.
Green - You may go on if the way is clear. Take care if you mean to go left or right and give way to pedestrians who are crossing.
Amber - Stop at the stop line. You may only go on if the amber appears after you have crossed the stop line or are so close to it that to pull up might cause an accident.

De facto:
Red - Curse the lights, your bad luck, other road users, pedestrians, and life in general.
Red + Amber - Slip into first, start crawling forward, and aim to cross the stop line and floor it the instant the light turns green.
Green - Go.
Amber - Go faster to get over the stop line before the light turns red.

Thanks again,

Robert