Set the size you want your digits to be and click the pixels to toggle them from black to white to create your own digit design.
Press "generate string" to generate a factorio blueprint string containing the appropriate circuitry for your digit display.
The display will show the value of signal A on a red wire connected to the one protruding lamp on the side of the blueprint.
Whenever you want multiple digits, simply place multiple digits next to eachother with that one protruding lamp overlapping the next blueprint.
The input signal should always be connected to the rightmost digit of the display.
(*Powerpoles not included)
There is currently a limitation to the maximum amount of pixels the digits can contain.
The height mutiplied by the width of a digit cannot currently exceed 109,
since there's only so many signals in factorio that can be used to encode information.
There is a solution to this, but I haven't implemented it yet, and I don't know whether I will.