You latch on a bit so that the signal is saved UNTIL the opposing green light timer starts (when the adjacent RED is ON and it is safe to cross). You don't need more timers for this, but only to use the existing switches I:1/0 and I:1/1 as pushbuttons to signal that a pedestrian wants to cross. Your pedestrian crosswalk logic went down the wrong path. The logic is essentialy the same as you had it and it will not work until you make the suggested corrections. Then I wrote rung comments describing what corrections you need to make for each rung (if any). That is where you use the same Output Energize (OTE) more than 1 time in a program. I took 3 of your programs and simply moved the rungs into some logical order (when the dreaded double-coil syndrome became obvious). Or you can fiddle around with trial-and-error for a long time before you hit the right combination. If you can correctly describe what it needs to do, then writing the logic is much easier. Yes, and the basic methods are to describe your rung FIRST, then write the logic.
I know I will need to add the overlapping red light coverage, but I just wanted to first grasp the basic method(s) first. Rung 12: By his description, Rung 5 & 6 should have been like this also? Besides safety precaution, as far as operation goes, do they both need to be active to start the timer? Rung 10 & 11: Are those safety measures needed and does it make any difference in the operation Rung 5 & 6: He mentions in his lab that he wait for both Vred & HGreen to be lit before beginning timer,īut has the in a OR configuration, not AND Rung 2 & 4: Why t/4? I understand to loop the cycle, but how exactly does the logic accomplish that? My questions are basically, those that are not explained in the lab, as all other ones are and I can understand that logic, but not the latching logic? He explains every step along the way, as he created the rungs, but does not mention the latches below the rungs he is describing, which does not explain why he inserted those to begin with. I want to fully understand the logic, and able to understand other solutions approaches, so I can have more understanding of the logic executed and why. Can anyone elaborate on Phil's Traffic Control Lab solution from his lab book? I was able to complete the lab using sequential timers and looping to get the same result, without any issues.Īlthough after seeing his solution, which is easy to follow, there are a few areas where I am getting confused and cannot grasp how certain logic is in place.
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