Follow the steps below to add an Excel spreadsheet to a Display board:

save excel spreadsheet in html format
to add the web link to the display board:
place test.html in ssl data - global admin
enter following URL in the display board
http://192.168.0.1:81/test.html
if you want to display a graph create a folder and specify that in the URL
http://http://192.168.0.1:81/test/test.html