Again the versatile workhorse IC 4017 comes to our aid and helps to make the project look much simpler.
You may refer to the article here to get a comprehensive overview of the IC 4017, and it will also help you to understand the present circuit better.
Looking at the schematic we see that four of the above ICs are connected so that they conduct in tandem. Each IC handles a single alphabetic character and is responsible for shifting it sequentially through the entire length of the display panel (8 slots).
For example, the outputs of IC1 are connected to the each individual display (total 8 displays) sequentially so that its “running" outputs illuminate only the letter “S" of “StOP". Similarly IC2 will do the same as IC1 but with the letter “t", IC 3 will sequentially light up the letter “O" and IC4 will “chase" the alphabet “P".
As explained, the above operations will happen exactly in tandem, i.e. the letter “t" will appear after “S" has jumped one digit – "O" will appear after “t" has moved a slot ahead and finally “P" will show up, creating a perfect display of the word “Stop" sailing/cycling smoothly over the entire length of the panel.
Let’s inspect the circuit more precisely:
Initially when power is switched ON, C1 resets the whole circuit so that pin #3 of all ICs becomes high (first pin out of the individual sequences).
At this very instant the high logic of pin #3 from IC1 holds pin #15 of IC2 and keeps it locked, similarly pin #3 of IC2 “freezes" IC3 and so on.
However in response to the input clocks, the moment IC1’s output shifts from pin #3 to the next sequence (pin #2), it releases IC2 from the binding.
Therefore as the output of IC1 proceeds from pin #2 to pin #4, IC2’s output jumps from pin #3 to the next sequence @ pin #2, releasing IC3 from the shackles, the process continues until IC4 also starts moving in sequence.
Since IC1 was the first to begin, its output sequence reaches its last pin out #11 first in the lot and latches with its pin #13 and “freezes", next one to follow the procedure is IC2, then it’s the turn of IC3 and finally IC4.
However, IC4’s pin #11 is connected to pin #15 of the IC1, simply means that the moment IC4’s pin #11 reaches logic high, it resets IC1 and the whole sequence. The circuit position reaches its initial status and the cycle repeats all over again.
The adjoining diagram of a classic LED advertising display illustrates the wiring connections required to build the scrolling word "StOP" as discussed in the article as an example. (Click image to enlarge.) All diodes are = 1N4148.
A single display slot diagram is shown here, consisting of separate inputs for each portion of the alphabet of the word “StOP". You will need to build eight such identical units. Since IC1 is handling the letter “S," all the relevant letter inputs from the eight displays will go to the outputs of IC1 sequentially from right to left. Similarly all the “t" characters should be integrated with IC2 in the above manner and so on. The wiring is complicated, so it definitely will need to be done over a well-designed PCB.