Q: How can I setup a macro that types a special character when I press a key on the keyboard?

I have an aplication where I am unable to insert a tilde (~) by pressing alt+Ñ. (I have a spanish keyboard) The only way this app lets my input a tilde, is by copying and pasting it in, which is extremely annoying and time consuming. 

Is there any way I can setup a script in Automator, or by any other means, that will automatically insert a tilde whenever I press a single key, such as a Function key? Or maybe I can make it so that whenever I type 'tilde' it will replace that with ~ ? I already tried using a keyboard shortcut (below) but it did not work.