In a large bowl, whisk flour, baking powder, baking soda and salt. In another bowl, whisk buttermilk and eggs until blended. Add to dry ingredients; stir just until moistened. Stir in butter. , Pour about 3/4 cup batter onto a lightly greased preheated waffle maker. Sprinkle with a few pecans. Bake according to manufacturer's directions until golden brown. Repeat with remaining batter and pecans.