I was interest on the Technics to build a digital Watt meter. I find a interesting schematic in the Internet from DL6GL. He share the Atmel program too.
So I take a Atmel Chip and a 2 Lines Display to try to build one.

Thanks to DL6GL for sharing this !

The finish Watt meter after start up

This is my self made measuring bridge

The measuring bridge in a case

A test with the FT-817

The watt meter works good, but it only usable up to 100 watts. I think you can use it for higher ranges, if you make the circuit board better then I.

Here is the manual to build the measuring bridge from DL4JAL: messkopf

Here is the Schematics from DL6GL

Get the complete files from http://dl6gl.de/