View Full Version : Traffic Lights Again

June 4th, 2002, 03:10 PM

Allen Nelson
June 4th, 2002, 03:19 PM
Originally posted by Tom Jenkins
I have several ideas.

First, do a search on this site. Traffic light problems abound, as they appear to be the most common application for PLCs, far exceeding slicing pickles, for example.

Second, you need to make a list of all of the inputs and outputs for the system - that is, a detailed list of everything that the PLC is turning on (outputs like Green North, Amber South, etc.) and signals it is receiving (penguin at south east crosswalk, for example.)

Then, you need to go to your text, and find out what makes a timer time, and an output turn on, and a contact close.

Then you need to write a detailed description of each step in the cycle.

Then you need to read the tutorial on this site.

Then you need to replace each event in your description with the corresponding ladder logic command (on = contact closed, for example).

This was the first reply to the first of three traffic light requests. Perhaps you can be the first, IN THE HISTORY OF PLCs.NET!!! to follow these instructions. Someone says something like this at every student post. Students are the ones who moan, not us.

June 4th, 2002, 05:31 PM
Originally posted by Goody
I hear M Mouse is an expert at such things, maybe he can help


June 4th, 2002, 10:41 PM
i divided my lights up into four counters;
red yellow yellow green
counter1 *
counter2 *
counter3 *
counter4 *

June 4th, 2002, 11:12 PM
I dont know why my graph didnt post
I took counter 1 to control the green light on road "A" and red on road "B".
I took counter 2 to control the vice-versa of counter 1
then I took counter 3$4 to control the yellow while leaving
the red light on the opposite street still on; til yellow goes out

Eric Nelson
June 4th, 2002, 11:35 PM
Originally posted by babybylar
I dont know why my graph didnt post
If you are including an attachment, make sure that after you've selected the file you click "Submit Reply" and not "Preview Reply"... Previewing will clear the "Attach File" location, and you'll have to re-specify the attachment...

June 5th, 2002, 01:38 AM
Try to make a Grafcet or something on which you could easly reason. I included one I use to teach my students to THINK! Once you have reasoned it out, then - AND ONLY THEN - start to build your program.

June 5th, 2002, 03:51 AM
I wish I had a 72 inch monitor to see that.

Eric Nelson
June 5th, 2002, 04:21 AM
Originally posted by Scooter
I wish I had a 72 inch monitor to see that

Good one Scooter! I'm guessing their motto is...

"BELGIUM... We're a Small Country, but we have BIG Monitors!".... http://atypically.net/smilies/goofy.gif


Rick Densing
June 5th, 2002, 08:04 AM
It looks fine on my 64 :)

June 6th, 2002, 02:36 AM
Sorry Scooter and Eric, but her in Belgium we also don't have 72 inch monitors. I guess it was the combination of a shortage of time and that **** Murphy's law. I hope this is somewhat better, I seem to be unable to preview a reply with the attached file, I only get a look at the reply without the image.

April 18th, 2005, 08:11 PM
hello all i am doing a final project for school can anyone give me some tips on getting the ladder logic for street lights. i would greatly appricate it.

April 18th, 2005, 08:53 PM
Rodney, Did you even read the PREVIOUS POSTS?!!?David

Steve Bailey
April 18th, 2005, 08:57 PM
So this guy walks up to a cop in Manhattan. The guy asks the cop "How do you get to Carnegie Hall"? For the cop's answer, scroll down.


The same advice applies to ladder logic for the traffic light.

April 18th, 2005, 10:17 PM

You don't have a rear projection screen system?

Eric Nelson
April 18th, 2005, 10:30 PM
Wow, this is an old thread. At least the newer members get to see where the term "Belgian Monitor" originated... :D



April 19th, 2005, 02:27 AM
Maybe word leaked out that they use PLC's in Belguim to control traffic lights.

That sounds so modern, maybe we should promote it heare in the states, Cananda, and in OZ. it could open up a whole new field for many of us. Now, how long is the green light supposed to be, before the guy behind you honks his horn?

NOTE TO ERIC: since you did such a fime job on the AB-Bash smiley, perhaps you can do one for traffic lights! Now for the poll, all in favor, press or speak "one", all oposed, press or speak "one".

All in favor of "hotwiring" PLC instructors, who assign traffic light problems, or ask for three types of PLC's, just smile quietly, smirking permitted, also.


Eric Nelson
April 19th, 2005, 03:51 AM
NOTE TO ERIC: since you did such a fime job on the AB-Bash smiley, perhaps you can do one for traffic lights! Now for the poll, all in favor, press or speak "one", all oposed, press or speak "one".

I have added it as item #837645 on my 'to do' list. While you wait, you'll have to make do with this... http://pages.prodigy.net/indianahawkeye/newpage16/20.gif



April 19th, 2005, 09:09 AM
you can use a sequencer output if you are using Rs logix. It can be accomplished in two rungs. You have to have a timer and some XIO and XIC adressed to your timer done bits. To control the lights you need to edit your N7 integer file. That's all the hints I'm willing to offer (lol) you can do the rest.

April 19th, 2005, 03:45 PM
N7 integer file.

I think that is what I use to clean relay contacts.

ERIC: Thank you, that will do for now. I'll remind you again next week. A traffic light with the Intenational "NO" slash/circle over it would be nice, also!

best regards.....casey

April 24th, 2005, 02:29 PM
How come all the students doing traffic light pgm's need them by tomorrow?

(Don't get me wrong, asking for help & needing it is ok, BUT last day thing just gets to me)

We had to learn without help in the old days, time for y'all to learn how to do it yourself and NOT wait for the silver platter to be handed to you.