Matseng is currently developing a power line frequency, and voltage monitor. The design is meant to monitor the quality of the line power and log to an SD card for later computer analysis. He is sharing his development through GitHub and discussing it in the forum.
I’m thinking of doing this project on two separate boards. One small board that measures the power line and sends the data to the display and storage board.
The main board would have a 7-segment display that would look something like the image below, showing the current time ( according to the time kept by the controller and OCXO), the number of seconds the time derived from the powerline frequency vould be off from the real time, and the current frequency + voltage of the power line.
The data would be logged in a SD memory card for later download via USB to a computer for graphing and analysis.
Via the forum.