@ -77,19 +77,20 @@ Decentralised (peer-to-peer) systems\cite{vu2009peer} are harder to build but ar
Using centralised system means, that the measuring devices will use one separate accessory, from now called the \textbf{server node}, to do most of the work on the software side. The work includes, but is not limited to, receiving the measured data, storing them, hosting the web server with the \gls{gui} containing all necessary options and information, handling the \gls{usb} or communication with a \gls{cloud} and so on. The block diagram for a server node, depicting required blocks can be seen in the figure \ref{f:serv_node})
Where there are at least two nodes in a system, they have to communicate together in a particular way, known to both of them. The web server naturally operates over \gls{tcpip}. Therefore, same networking stack (the way of comunication), that is used for communication between the server node and user can be used to communicate to client nodes as well. \Gls{tcpip} hardware is ready to be used and is supporting a full-blown networking \gls{stack}, powering communication over today's networks.
Where there are at least two nodes in a system, they have to communicate together in a particular way, known to both of them. The web server naturally operates over \gls{tcpip}. Therefore, same networking stack, that is used for communication between the server node and user can be used to communicate to client nodes as well. \Gls{tcpip} hardware is ready to be used and is supporting a full-blown networking \gls{stack}, powering communication over today's networks.
The measuring devices, from now on called \textbf{client nodes}, will consist of blocks of the remaining hardware requirements. The resulting block diagram can be seen in the figure \ref{f:client_node})
\subsection{Hardware components breakdown}
For the \textbf{server node}, a complete working solution already exists, ready to be employed. The \textbf{GL.inet board}, described in more detail in the chapter \ref{s:glinet}, is greatly sufficient in all required aspects, and thus should be used for this purpose.
For the \textbf{server node}, a complete working solution already exists, ready to be employed. The \textbf{GL.inet board}, described in more detail in the chapter \ref{s:glinet}, is greatly sufficient in all required aspects, and thus is used for this purpose.
Luckily, a particular part of the required functionality for the client is already integrated as a \textbf{ESP-8266 module}, described in more detail in the chapter \ref{s:esp8266}. The module contains the \gls{tcpip} stack, micro-controller (application processor) running the user program, \gls{wlan} and light indication, all in one piece, so this greatly simplifies the design process and allows for more focus on the actual measurement circuitry. The actual ESP-12E module should be used, because of the available certification\cite{online:2ADUIESP-12}, which allows it to be introduced on the market later. It was shown in the figure \ref{f:esp-12e}. The \gls{pwm} is present there too, so sound indication requires just an additional sound emitting device.
Talking about the measurement circuitry, the viable candidate is MAX78615 \cite{online:MAX78615} with the companion \gls{ic} MAX78700 \cite{online:MAX78700}. The couple \ref{f:schem_block} should be used, because it provides multiple ways of same voltage level communication with the processor, galvanic isolation via the pulse transformer for improved circuitry protection, great precision, accuracy and utility. The shunt resistor is utilised as a way of obtaining measurements, described in the sub-chapter \ref{ss:pmic}.
Luckily, a particular part of the required functionality for the client node is already integrated as a \textbf{ESP-8266 module}, described in more detail in the chapter \ref{s:esp8266}. The module contains the \gls{tcpip} stack, micro-controller (application processor) running the user program, \gls{wlan} and light indication, all in one piece, so this greatly simplifies the design process and allows for more focus on the actual measurement circuitry. The actual ESP-12E module has been chosen, because of the available certification\cite{online:2ADUIESP-12}, which allows it to be introduced on the market later. It was already shown in the figure \ref{f:esp-12e}. The \gls{pwm} is present there too, so sound indication requires just a sound emitting device.
Luckily, a particular part of the required functionality for the client node (displayed as a simplified schematic in \ref{f:schem_block}) is already integrated as a \textbf{ESP-8266 module}, described in more detail in the chapter \ref{s:esp8266}. The module contains the \gls{tcpip} stack, micro-controller (application processor) running the user program, \gls{wlan} and light indication, all in one piece, so this greatly simplifies the design process and allows for more focus on the actual measurement circuitry. The actual ESP-12E module has been chosen, because of the available certification\cite{online:2ADUIESP-12}, which allows it to be introduced on the market later. It was already shown in the figure \ref{f:esp-12e}. The \gls{pwm} is present there too, so sound indication requires just a sound emitting device.
@ -99,9 +100,28 @@ Luckily, a particular part of the required functionality for the client node (di
\caption{Greatly simplified schematic of a \textit{client node} sketching the inner working}\label{f:schem_block}
\end{figure}
For the protection against fire a standard electric fuse or a resettable \gls{ptc} fuse\cite{wright2004electric} should be used. The circuit protection against high voltage should be solved with an isolated DC-to-DC converter\cite{carr1996linear} or with the linear transformer coupled with the linear voltage regulator\cite{2008linear}. Since the former one is either expensive or hard to design, the choice should fall on the latter.
For the protection against fire a standard glass fuse or a resettable \gls{ptc} fuse\cite{wright2004electric} should be used. Because of the variable nature of most devices, it is hard to calculate the current consumption of the circuit. It can be measured after the first iteration is manufactured. Thus, the easily replaceable standard glass fuse has been chosen because of its versatility. The circuit protection against high voltage should be solved with an isolated DC-to-DC converter\cite{carr1996linear} or with the linear transformer coupled with the linear voltage regulator\cite{2008linear}. Since the former one is either expensive or hard to design, and this work does not want to focus on more complexities, the latter option has been chosen.
Choosing the voltage level for the digital electronics (the output voltage of the linear regulator) is straightforward. Since the ESP-12E works on nominal 3.3V, this is the level that has been chosen. Having \glspl{ic} using the same voltage level removes the need to level-shift the communication between them, thus increasing the simplicity of the design.
Talking about the measurement circuitry, the candidate is MAX78615 \cite{online:MAX78615}, working on nominal 3.3V level, along with the companion \gls{ic} MAX78700 \cite{online:MAX78700}. The couple has been chosen, because it provides multiple ways of communication with the processor (buses), galvanic isolation via the pulse transformer for improved circuitry protection, great precision, accuracy and utility. The resistor network, including the shunt resistor is utilised as a way of obtaining measurements. The shunt resistor is also briefly described in the sub-chapter \ref{ss:pmic}.
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.
\caption{The top layer of the designed \gls{pcb} (client node), exposing maintly \gls{tht} components}\label{f:pcb_top}
\end{figure}
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 the choice is obvious.
Peter Babič
8 years ago