The Grid-2-Audio module is comprised of three main parts:
1. The case and IEC all-in-one power entry connector - As part of teaching myself AutoDesk Inventor, I decided to start with the mechanical aspect of the project. The presence of mains voltage potential is no joke and the design of the case reflects that. The utilisation of an IEC power socket with built in switching, fusing and illumination minimises any mains wiring around the internal space of the unit.
2. The PCB power supply and mains input - As the unit is design to measure the grid voltage and introduce minimal noise, the power supply needs to ideally draw a minimal sinusoidal current (at the fundamental frequency) in phase with the voltage. Additionally, there needs to be isolation between the mains measurement circuit and the output side, forcing the requirement of multiple transformer taps for the whole PCB.
3. The PCB signal conditioning - The mains signal needs to be conditioned to the 3.5mm audio format and protected from shorts. As an extra feature, a 50Hz notch filter will be included to provide an alternate "harmonic only" output to increase the dynamic range for harmonic analysis.
Here is a quick mock-up sketch of the basic circuit:
Why yes! The harmonics high pass filter has been drawn as a low pass by mistake! :)