Add the Discovered problem subchapter

analytical.tex

@@ -104,7 +104,7 @@ Talking about the measurement circuitry, the candidate is MAX78615 \cite{online:
 The remaining part of the client node block diagram \ref{f:client_node} not yet mentioned is switching. Either a mechanical relay or a semiconductor device, such as a thyristor or a \gls{ssr} isolated by an opto-coupler\cite{trzynadlowski2015introduction} will do. Mechanical relays tend to be larger and produce sound noise, have slow response time, but have inbuilt separate isolation and are capable of switching higher currents without additional thermal issues than their semiconductor counterparts\cite{blume2008electric}. The disadvantages of the mechanical relay are not relevant here, thus it has been chosen.
 
 
-\subsection{Schematic and PCB}
+\subsection{Schematic and PCB} \label{ss:schematic_pcb}
 The detailed schematic can be seen in the figure \ref{f:schem_full}, along with the \gls{bom}, shown in the table \ref{t:bom}. Some parts of it are quite straightforward, but some require less or more description, to avoid confusion.
 
 \begin{figure}[ht!]

conclusion.tex

@@ -1,10 +1,10 @@
 \section{Conclusion}
 The main requirement of the work was to measure the real, reactive and apparent electric power, as well as power factor, and to show the values to the user, preferably, plotted as a quantity over time. It had to utilise the ESP8266 chip and the GL.inet board in the process. The work's requirements were, however, met only partially. The problem is caused by the inability of obtaining most of the sought values from the power measuring integrated circuit, the MAX78615 over the \gls{spi} communication protocol. As a result, only the apparent power could be displayed, subsequently preventing the requirements relying on the other required data from completion. All the attempts to resolve the problem with Maxim Integrated technical support resulted in dead end. The stated reason was, that the part in the question is no longer supported by Maxim. It was sold with all the accompanying parts to the Silergy Corp. in the critical part of the firmware development. Despite of the problems, all the remaining requirements that could be rationally implemented were met.
 
-Another big problem is erratic start of the client device after it has been plugged in to the socket. Investigations of the power supply allowed to slightly reduce the frequency of failed starts but there is more work to be done to eliminate the phenomenon completely. This problem makes device really unreliable to use.
+
 
 \subsection{Possible future improvements}
-The most crucial thing to improve is to make the client node's start reliable. The ESP-12E module sometimes won't start, but without any evident mark on the oscilloscope, probing its supply voltage. It may be the power supply problem or it may be some firmware problem. After this problem has been adressed, one can move on to some other issues, but not before.
+The most crucial thing to improve is to make the client node's start reliable. The ESP-12E module sometimes won't start. After this problem has been resolved, one can move on to some other issues, but not before.
 
 It is possible to fulfil all the failed requirements due to inability of accessing all the data over \gls{spi} by switching to \gls{i2c}. The only downside of such a design is inability to obtain all the instantaneous measurements. This is not a problem at all, because a lot of them still lies in the region inaccessible by \gls{spi} (\gls{spi} is the only protocol fast enough to be capable of reading instantaneous measurements before they are being over-written at a sampling frequency - this should be fixed by the \gls{ic} manufacturer). The frequency at which \gls{i2c} is capable of obtaining measurements is perfectly sufficient anyway. Also, \gls{i2c} requires one less pin than \gls{spi}, thus leaving more pins on the ESP8266 for additional features. Such a transition would however definitely require another iteration of the \gls{pcb}, which is not instant and requires a bit of resources. If a project is to be maintained in the future, this is definitely a vital change.
 

mainpart.tex

@@ -1,5 +1,35 @@
 \section{Realisation}
 
+The manufactured client node has been inserted into the enclosure containing an European mains socket (female) on one side and an European mains plug (male) on the other side, forming a man-in-the-middle adaptor, that can be non-invasively put between wall socket and an appliance. The result can be observed in figure \ref{f:project_inside}.
+
+\begin{figure}[ht!]
+\centering
+\includegraphics[width=.7\textwidth,angle=0]{project_inside}
+\caption{The view into the client node's enclosure, before the final assembly}\label{f:project_inside}
+\end{figure}
+
+\subsection{Discovered problems}
+
+After a few test runs performed on an assembled client node, the first problem became obvious: the node's application processor (contained inside of the ESP-12E module) starts erratically, when the node is plugged into socket. Investigations of the supply voltage under the oscilloscope shows no difference in voltage surges during the boot-up, either if the processor starts or not, suggesting a firmware problem too. The first 220ms of power line inspection can be seen in the figure \ref{f:oscilloscope}. However, this problem does not occur, when the processor is powered from external source via J3, but otherwise makes the node unreliable to use. 
+
+\begin{figure}[ht!]
+\centering
+\includegraphics[width=1\textwidth,angle=0]{oscilloscope}
+\caption{The power line of the ESP-12E inspected during the boot-up by the oscilloscope - it looks the same either if the processors boots, or it doesn't, suggesting the possible occurence of the ESP8266 firmware problem}\label{f:oscilloscope}
+\end{figure}
+
+Ignoring the boot-up problem, the client node is sort of working as indented, apart from one huge problem with the MAX78615 \gls{ic}, that was not apparent during the design stage: the \gls{spi} protocol only allows for 6 bit long memory addressing, enabling only the first 64 words of the memory to be accessed, leaving the 104 words out of 186 completely inaccessible. As a result, from the required data, only RMS Voltage and RMS Current can be obtained. All the data depending on phase shift, namely real power, reactive power and power factor are not accessible. 
+
+The \gls{spi} limitation obviously cripples the node's functionality. The protocol was chosen, because the data-sheet for the MAX78615 suggested it as the only way to obtain the instantaneous measurements, as discussed back in the sub-chapter \ref{ss:schematic_pcb}. Although the instantaneous measurements are not required, there was no reason to not enable this feature in the design stage. The fact, that such a limitation exists was observed too late.
+
+Requesting help from the technical support of the \gls{ic} manufacturer, the Maxim Integrated, did not help resolve or at least minimize the damage. They responded, that they are no longer supporting the part in question, because whole power measurement department was sold to another manufacturer based in China, Silergy Corp in March 2016. 
+
+There are multiple, rather cosmetic issues, that does not affect the functionality of the board, but are imposing small physical troubles. They include the following:
+\begin{itemize}
+\item The J3 header is wrong pitch (2mm instead of 2,54mm)
+\item The mounting holes are too small diameter
+\item The longer side of the board is 1mm wider than desired, it doesn't fit easily into the enclosure
+\end{itemize}