Soak urad daal and barley for 5-6 hours in a good amount of water.
Grind to make idli batter. Add idli rava and mix it well.You can make idli immediately or keep it for fermentation and then prepare.
Add salt just before making idli.
Pour big spoon full of batter to idli maker and steam it for 12-15 minutes. Serve hot with chutney or your favorite gravy.