A convenient adapter to view the electrical grid waveform through your PC's sound card.

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There is a lot to be observed from the waveform of the electrical mains. Harmonics, transient changes, periodic fluctuations, frequency shifts, impedance, power line communications - These all give clues as to the state of the country's electrical transmission system (or what loads your neighbour has connected). Platforms like MATLAB allow for the easy analysis of waveforms through powerful software tools, but only once the signal has been acquired.

The purpose of this project is to allow easy and safe access to the electrical grid waveform without a hassle. It's as simple as power cable in and 3.5mm audio out.

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! :)

  • Case Completion

    David Scholten5 days ago 0 comments

    For this project I've taken the reverse approach or designing the case before the PCB itself. In this way I've imposed at least some design limitations to stop the scope getting out of hand and forcing a completion for the project.

    Apologies for the Inventor screenshot interface overlays, but here is the front and central sections of the casing in inventor:

    And here is the implemented 3d print: (Prusa i3 "MK1"):

    I designed the case in an extrusion style with a faceplate, but the 3d printing manufacturing technique also allows for lateral features like cooling vents or indents for rubber feet (of which there are 4). Ports A and B are for the direct grid output and the 50hz notch filter output. The PCB itself will slide in along notches along the wall like traditional aluminium extrusion cases.

    You may have noticed the two colour printing on the front plate, which is possible through a script provided from prusa that allows the printer to stop and change filament at a specified layer.

    For the back of the case (containing the IEC receptacle) I had to create a cap to hold it in place during disconnects:

    When implemented:

    All together I'm quite happy with the final appearance and will be quickly be moving through the circuit and PCB design phase (with an aim to have surface mount automated assembly performed through Seeed Studios).

    Final fun photo is a "cross section" of the entire enclosure using a portion of the case that I opted to print in two steps:

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