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Discussion Starter · #1 ·
In trade school now and we have to do PLC but due to Covid we basically have to learn it on our own. I'm having trouble figuring out how to get the bit to flash here. I've done most of the work but I cannot figure out the last part about getting the green light to flash after all the other timers are done. Can someone help? (Project 15 has nothing about flash bits)
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so you should have four steps lasting 5 secs each.
I would suggest that the flashing green goes after the green and before the yellow
using the LES and GRT s and your timer. you should be able to set up a half sec long flash (or what ever duration you like)
This should be a branch rung on O:2/0
 

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Discussion Starter · #4 ·
so you should have four steps lasting 5 secs each.
I would suggest that the flashing green goes after the green and before the yellow
using the LES and GRT s and your timer. you should be able to set up a half sec long flash (or what ever duration you like)
This should be a branch rung on O:2/0
But the assignment says to have the same green light come on again after the three have run their course except flashing so I don't think that would work.
 

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But the assignment says to have the same green light come on again after the three have run their course except flashing so I don't think that would work.
Ok so I didn’t look close which PLC you have. One fun thing about timers is that every one does them slightly differently to a fault.

Regardless you should know how to set up a rung to go true based on 3 different bits (3 bits in series). So if you put in an output coil the light would be steady on. But let’s just put two timers there. One for say 1 second and one for a half second.

Now trigger the light when the half second timer is done.

Reset the half second timer AND the 1 second timer when the 1 second timer is done.

If you prefer you can also use the normally closed but on the 1 second timer in series with both of the timers. So when the 1 second timer goes to some state it self triggers and both restart again. This is called a free running timer. It has a small timing issue in that the time is actually 1 second plus 1 scan. You can do some math to fix this but not worth it for flashing lights.
 

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But the assignment says to have the same green light come on again after the three have run their course except flashing so I don't think that would work.
1) It is stated to be a traffic lite, do you flash green after the red or after the green?
2) it says also have, nothing about after
3) it is your assignment, it will not upset me and i will not argue if you choose otherwise
4) I like Pauls idea for a free running timer, i just couldnt remember how to do it myself, so i didnt suggest it. You will still need to control when it is actively controlling the lite
 

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You are told to restart the sequence after the red lite ends. this wont fit with putting the flashing green last
Also i am not sure if they want you to use any more than the one timer listed in the instructions. It says use any of the comparison instructions, i dont know if they consider a timer as a comparison instruction

Best of Luck !!!! :)

PLCs are a boat load of easy fun once you get comfortable with them, I could sit in my electrical shack while accessing all of the PLCs in the mill and control any or all of the machines in the mill including over ride the operators inputs. Not that i would or should, just saying i could.

Just keep in mind that when you change things in a real world PLC it changes things in the real world machines, always spend a few minutes thinking about what else will happen if you do what you have in mind.
 

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Im guessing in project 15 you made a bit call "flash bit" probably addressed at the bit level b:01 or something like that. (does what it says and flashes at a set rate. All of my programs use a "blinky bit" as im to lazy to write lots of timers). That code has to included in this program.

So your new project is to make a 20 second timer and use comparisons to set 4 different states.

state 1: 0-5 seconds green solid 5 seconds
state 2: 5-10 seconds green flashing (as the bit in project 15 flashes just add that to the same rung)

Now you could combine state 1 and state 2 so green on 10 seconds but after 5 use the "flashing bit"

state 3: 10-15 seconds amber on solid
state 4 15-20 seconds red on solid

reset timer at 20 seconds, One of the problems this will tech you is the difference between GEQ and GRT commands. It may not show up with a time base in 0.1 seconds but if you change the time base to seconds you will notice how one reacts in 5 seconds and the other in 6 seconds.
(e.g GRT than 5 seconds is 6 seconds so you may end up with some lights overlapping or spaces where no lights are on)
 

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Discussion Starter · #9 ·
From what I understand it goes
5 seconds flash green
5 seconds green
5 seconds yellow
5 seconds red
Reset

I know it doesn't really match up with what the paragraph says but otherwise I can't see any other way to do it so I'm just gonna roll with it. gpop mentioned a "flash bit" which is something that was mentioned but never utilized so I think that's the way to go.

I redid it but still can't get it to flash. Anything I could think of, without a flash bit, involved a lot of timers and extra and I feel that's not the point of this exercise.

Just found this on my phone, he seemed to be going over it somewhere. Can anyone explain how he's getting the flash?
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