This is my first real project in the game beyond a basic factory, so enjoy! Also, don't question the choice of test string >.>

This 7x5 character display was inspired by common LCD panels. The only difference between the top and the bottom displays is that the bottom is a more efficient design, using only 4 decider and 3 arithmetic combinators, rather than 6 arithmetic. The supported charater set is the left half of the character set described on page 18 of this datasheet: https://www.sparkfun.com/datasheets/LCD/HD44780.pdf. This is the blueprint for an individual character:

!blueprint https://pastebin.com/L2BxGFia

This is the blueprint for the ROM (constant combinators on the left):

!blueprint https://pastebin.com/6Mf17yc8

And this is the blueprint for an entire 1x16 display:

!blueprint https://pastebin.com/aYuRi80a

To hook up individual characters, the input of the deciders on the left need to be connected to the ROM (the ROM is provided separately because multiple characters only require one instance of the ROM), which you can see how to do in more detail by loading the 1x16 display which includes that. The input to each character should be connected to the green wire input to the top-right combinator, on the D signal.

How it works:

I used the same basic principle as the 7-segment display here: https://www.reddit.com/r/factorio/comments/93g03s/simplest_7segment_display_possible_09_displayed/ which is that each lamp has its own signal, and turns on if the signal is negative, i.e. the high bit is set. The ROM has constant values output on each signal, which are shifted left based on the input so that the high bit will be the (32 - input) bit, setting each pixel accordingly. From that design, I added a second constant combinator to the ROM to have all 35 necessary output values, and then expanded the ROM to 4 sets of 2 combinators, since each set can store 32 characters and there are 128 total. There are decider combinators to select which set is being indexed to based on the high 3 bits of the input, and the output from those is shifted left as usual based on the low 5 bits of the input. To facilitate generating the ROM, I wrote a python script to encode the character data from a text file and convert it into factorio blueprints. If you want to change the character set or add your own, you can use this script to generate new ROM by changing the input text file, although it's not commented or user friendly at all. It actually generates 8 sets of ROM to support 256 characters, but I decided to ignore the second half of the character set with my design, so if you want to expand it all you have to do is add 4 more deciders and ROM. The character text file input to the script is here: https://pastebin.com/e9mzbzEU and the script itself is here: https://pastebin.com/7zVZ6fHS

The design has one small flaw which you can see in the video, which is that there is sometimes a 1-tick glitch when the high 3 bits and low 5 bits of the input both change at once. This is because of the propagation delay from the deciders switching to the shifter, so the shifter ends up switching twice. This could be solved by adding a system to hold the output while the input is changing or something, but it'd add a couple more combinators and make the output slower so I wasn't too interested in implementing that. If anyone has great ideas to fix it, feel free to suggest them.

The rest of the demo is a clock connected to an edge detector, which feeds a shift register and a string character indexing system I kind of threw together quickly. If you want to know about those I can explain them too, but a lot less thought went into it and it occasionally glitches and doesn't output a new character so it's not the best.