At DSIP Lab (Digital Signal and Image Processing Laboratory) of the ECE Dept, Univ of Patras, Greece, we are recording the Electrical Network Frequency (ENF) since July 2016. Data and code are made available for free download.
The Electrical Network Frequency (ENF) Criterion is a forensic technique used to identify the authenticity of a digital recording. Since the power line signal interferes with all kinds of recordings (telephone, video, biosignals, ...), the availability of the ENF signal data for Greece could facilitate the authenticity of a recording, and the time & place that this recording has taken place. This is made possible by comparing the frequency pattern between the background utility hum in the evidence and long-term records of the ENF.
We have ported the power line frequency recording system to a Raspberry Pi 3 Model B. This has rendered the whole system small in size, portable, and of low cost. The system captures the power line signal and extracts the ENF signal for mainland Greece, 24/7. The ENF data are uploaded every midnight to the cloud for free download. The recordings are in .csv file format.
More details about the system and the Python code for the Raspberry, can be found at http://dsip.ece.upatras.gr/projects/