adding to end of string based on another cell getting changed

ok so this one might be a little bit hard to explain but i will try my best

i have numeric values in columns D, H, K, N, and text in column AI.

when i increase the value of column D by 1 i would like a "W" to be added to the end of the text string in column AI.
when i increase the value of column H by 1 i would like a "L" to be added to the end of the text string in column AI.
when i increase the value of column K by 1 i would like a "T" to be added to the end of the text string in column AI.
when i increase the value of column N by 1 i would like a "O" to be added to the end of the text string in column AI.

and if possible i would like column AI to always only show the last 10 characters in the string (they can be deleted or just hidden, either way)

the numeric values in columns D, H, K, N are changed manually by me and always increase by 1 at a time and start at "0" and can increase up to a value of "80"

maybe a code that "adds 1" to selected cell, and then IF that cell is in column D adds a "W", in column H adds an "L", in column K adds a "T", and in column N adds an "O" (if that makes sense!?!)

if a sample workbook is need i can whip one up

thanks for the help

Hi Holger, thanks for the reply

ive attached a workbook for you to look at

when you ask about the upper limit do you mean the numeric values in D, H, K, N? because those dont need to be restricted, they are controlled by me.

i have a few other formatting events that happen when i update/change the values in DHKN, but other than that i think thats it

thanks

simply amazing!!!!

thanks so much Holger