I went online, (of course), and found some pictures of wooden shelf brackets, and with some modifications, designed my own. Here is the finished shelf at my son's house.
To the left is a closer view. He painted them black to match his decor.
Here is a closeup of the brackets. They are made from some 3/4 plywood I had laying around. If I make more of them, they will have to be made out of some other material, as I have no more of that particular plywood.
The radius of the brace part is from the bottom of a gallon paint can.
Here is a top view.
The part that goes on the wall is 1 7/8" wide x 10" long. The part that holds the shelf is 1 5/8" wide x 7 1/4 long. I broke the edges with a 1/4 radius cutter on my router table. I used #8 x 1-1/2 screws throughout, and each joint is also glued with Titebond interior wood glue.