Jeckson Ben,

From long ago training in poster materials I learned that for human readability you need at least one inch (25.4 mm) high characters at a distance of 25 feet (7.62 m). That guide would be for a font in all capital letters. Lower case needs to be about 40 to 60% taller.

You could use this as a starting point to figure out what type of LCD panel to utilize. If you do use an LCD it will have to be one with a lot of backlite intensity and a very large white/black contrast ratio.

There are some monochrome LCD modules you could consider taking a look at to see if the contrast ratio is high enough. For example the Tianma TM240128ABCWVBYD display offers enough display area to show two lines of large characters with six to seven characters per line. Thse may very well be nicely readable at 4 to 7 meters. Several displays could even be used side by side to enable multi-field information to be shown such as times, numbers, routes or weights...etc).

Michael Karas