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-\documentclass{article}
-\usepackage{graphicx}
-\usepackage{hyperref}
-\usepackage[backend=biber]{biblatex}
-\usepackage{amsmath}
-
-\title{\textsc{Comp} 490 Mid-Term Report}
-
-\author{Sam Anthony 40271987 \\
-sam@samanthony.xyz \\ s\_a365@concordia.ca
-\and
-Hovhannes Harutyunyan, PhD \\
-Department of Computer Science and Software Engineering \\
-haruty@encs.concordia.ca
-\and
-Concordia University \\
-}
-
-\addbibresource{references.bib}
-
-\begin{document}
-
-\maketitle
-\tableofcontents
-\pagebreak
-
-
-\section{Project introduction}
-
-The goal of the project is to build an electronic device for use in cars: it is an interface between the car's CAN bus (controller area network) \cite{can20b}, and some analog gauges installed in the cockpit.
-An overview of the system is shown in Figure \ref{fig:system}.
-
-\begin{figure}
-	\centering
-	\includegraphics[width=\textwidth]{"../proposal/diagram.png"}
-	\caption{System diagram.}
-	\label{fig:system}
-\end{figure}
-
-
-\section{Desiderata}
-
-The device must be able to perform certain functions.
-As well, there are some desirable properties that it should fulfil.
-
-These function and desirable properties are as follows:
-
-\begin{enumerate}
-	\item{Receive standard and extended CAN frames from the bus.}
-	\item{Decode information in the frames.}
-	\item{Generate four analog 0--5V signals suitable for driving temperature or pressure gauges.}
-	\item{Generate two variable-frequency square waves for a tachometer and a speedometer.}
-	\item{Be user-programmable for any encoding scheme and gauge combination.}
-	\item{Run on a 12V automotive electrical power supply.}
-	\item{Operate reliably in an automotive environment: resist heat, vibration, and EMI (electromagnetic interference).}
-\end{enumerate}
-
-
-\section{Component selection}
-
-A car is a harsh environment for an electronic device.
-The device is subject to large variations in temperature, vibration, and EMI.
-To increase reliability, AEC-certified parts were chosen wherever possible.
-
-
-\subsection{Logic control}
-
-The microcontroller is at the heart of the design.
-A Microchip PIC16F1459 was chosen because of its simplicity and robustness, its feature set, and its low cost \cite{pic16f1459}.
-It is an 8-bit microcontroller that features a USB peripheral for communicating with the host PC, an SPI peripheral for communicating with the other ICs, and timers for waveform generation.
-The PIC is a proven design that Microchip recommends for automotive applications.
-It is available in a DIP package, making it convenient for prototyping on a breadboard (Figure \ref{fig:pic}).
-
-\begin{figure}
-	\centering
-	\includegraphics[width=0.5\textwidth]{"pic16f1459.png"}
-	\caption{Microchip PIC16F1459 8-bit microcontroller.}
-	\label{fig:pic}
-\end{figure}
-
-A Microchip MCP2515 serves as the CAN controller \cite{mcp2515}.
-It supports CAN 2.0B up to 1Mbps and it has an SPI interface for communicating with the PIC.
-An MCP2561 transceiver goes along with it \cite{mcp2561}.
-Like the PIC, both these chips are available in DIP packages for prototyping on the breadboard.
-
-
-\subsection{Data storage}
-
-The EEPROM is used to store the configuration.
-This includes the encoding scheme that defines how parameters are encoded in CAN frames, as well as a table that maps parameter values to output signal values.
-
-There are six such tables: one for each gauge.
-Each table has 32 entries, and the mapping is between 16-bit words.
-Thus, the required size is $6 \times 32 \times 16 \times 2 = 6144$ bits, or 768 bytes.
-The encoding schemes will take a handfull of bytes per gauge in addition.
-
-a Microchip 25LC160C EEPROM was selected.
-Its 16Kib (2KiB) of space is more than adequate to hold the configuration.
-
-
-\subsection{Input/output}
-
-The PIC has an integrated USB peripheral for communicating with a host computer.
-The configuration is sent to the PIC via USB and stored on the EEPROM.
-
-Four DACs (digital-to-analog converters) generate analog signals to drive the four pressure or temperature gauges.
-Based on the characteristics of commonly-used pressure and temperature sensors \cite{bosch_pst}, it was determined that a resolution of 15mV/step was required.
-Given the operating voltage of 5V, this meant that the DACs must have at least $5\text{V}/15\text{mV} \approx 333$ steps of resolution.
-Thus, an 8-bit DAC with 256 steps would be insufficient, and so a 10-bit DAC was selected: namely a Microchip\footnote{It is purely a coincidence that all the ICs ended up being Microchip parts. I don't have any particular affinity to the company. It just so happens that they make all the right chips for this particular application.} MCP4912.
-The MCP4912 incorporates two DACs in a single chip, so there are two chips per board.
-
-
-\subsection{Power supply}
-
-The ICs require a 5V supply.
-
-A 12V automotive electrical system operates in a wide range of approximately 9--16V, with a nominal voltage of $\sim$13.7V.
-The voltage ripple is often quite significant as well.
-Thus, the power supply must be very robust to supply a stable voltage to the ICs.
-
-The voltage drop $V_\text{Drop} = V_\text{In} - V_\text{Out}$ is $16\text{V} - 5\text{V} = 11\text{V}$ in the worst case.
-This ruled out the use of a linear regulator, since it would dissipate too much power.
-The power dissipation of a linear regulator is linear in $V_\text{Drop}$:
-
-\begin{equation}
-	P = (V_\text{In} - V_\text{Out}) \times I
-\end{equation}
-
-The load current is estimated to be $\le 250$mA \cite{power_budget}.
-That means a linear regulator would dissipate up to $11\text{V} \times 0.250\text{A} = 2.75$W.
-That amount of power from a single chip would be difficult to cool.
-Thus, a switching regulator is the right choice for this design.
-
-The downside of a switching regulator is that it produces a lot of noise in the PDN (power distribution network).
-To isolate the other components from this noise, a two-stage PDN is used.
-The first stage is the switching regulator itself, also known as a buck converter.
-The buck drops the voltage from 12V down to 7V.
-
-The second stage is composed of two linear regulators: one for the digital circuitry, and one for the analog circuitry.
-The linear regulators drop the voltage from 7V down to the final 5V that the ICs require.
-
-Just like a buck converter, switched digital ICs introduce noise into the PDN.
-Therefore, it is good practice to keep the digital and analog components separate.
-The second power stage isolates the ICs from the noisy buck converter, and splitting the stage between two regulators keeps the digital and analog circuits isolated from one-another.
-This design is certainly overkill for the application, but it is better than using too weak of a PDN that delivers an unstable voltage.
-
-The buck converter is a Texas Instruments TPS5430 \cite{tps5430}.
-It is surrounded by a couple of LC and RC networks to regulate the voltage and to dampen the output ripple.
-See the datasheet and \cite{power_supply} for the process of selecting the accompanying passive components.
-The linear regulators are a pair of ST L78M05ABs \cite{l78m}.
-
-
-
-\section{PCB design and manufacture}
-
-KiCad was used to design the schematic (Figure \ref{fig:schematic}) and the PCB (Figures \ref{fig:pcb_pours} \& \ref{fig:pcb_3d}).
-JLCPCB was chosen to manufacture the printed circuit board.
-At the time of writing, the board design has been finalized and submitted to JLC for manufacturing.
-It should arrive any day now.
-
-\begin{figure}
-	\centering
-	\includegraphics[width=\textwidth]{"schematic-v0.2.pdf"}
-	\caption{Schematic.}
-	\label{fig:schematic}
-\end{figure}
-
-\begin{figure}
-	\centering
-	\includegraphics[width=\textwidth]{"pcb_pours-v0.2.pdf"}
-	\caption{PCB front and back copper pours; drill holes.}
-	\label{fig:pcb_pours}
-\end{figure}
-
-\begin{figure}
-	\centering
-	\includegraphics[width=\textwidth]{"pcb_3d-v0.2.png"}
-	\caption{3D render of the PCB.}
-	\label{fig:pcb_3d}
-\end{figure}
-
-The board is a 4-layer design that uses a combination of surface-mount (SMD) and through-hole (THT) components.
-The top and bottom layers are for signals, and the two middle layers are solid ground planes.
-This ensures that all signal traces' fields are tightly coupled to ground directly above or below.
-Power is routed on the bottom layer.
-
-As mentioned above, most of the ICs are available in DIP (through-hole) packages, and I have been using them for prototyping on the breadboard (Figure \ref{fig:breadboard}).
-Once the PCB arrives, I can transplant the chips into the board, along with the passive components.
-
-\begin{figure}
-	\centering
-	\includegraphics[width=\textwidth]{"breadboard.jpg"}
-	\caption{Breadboard circuit for MCP2515 system testing.}
-	\label{fig:breadboard}
-\end{figure}
-
-The power supply parts, on the other hand, are SMD.
-It is important to minimize loop lengths in power supply circuits.
-That is why power regulator chips are generally only available in smaller SMD packages.
-The SMD components will be assembled by JLC, as I have neither the equipment nor the skill for SMD soldering.
-
-The board was layed out with PCB design best-practices in mind.
-Traces are widely-spaced to reduce coupling.
-All signal vias are accompanied by a ground via to keep the electric fields from spreading in the dielectric.
-All traces are microstripped above a solid ground plane, again to keep the fields tight and to give the current a return path.
-The noisy switching regulator is placed far away from the other components to reduce EMI---the sensitive analog signals and the DACs are on the opposite side of the board.
-
-
-\section{Firmware}
-
-Firmware is the program that runs on the PIC microcontroller.
-It is responsible for interacting with the peripherals and transforming data from the CAN bus into output signals for the gauges.
-
-The firmware is written in C for Microchip's XC8 compiler \cite{xc8}.
-
-Each peripheral---MCP2515, 25LC160C, and MCP4912---has a corresponding translation unit.
-So far, I have written and tested the MCP4912 DAC unit.
-The 25LC160C and MCP2515 units are mostly written but still require more testing.
-
-The firmware must also communicate with a PC via USB.
-The Microchip MLA USB library is employed for this purpose \cite{mla_usb}.
-However, the USB code uses a lot of the PIC's flash memory.
-Some system test builds already fail to link due to lack of space.
-As a result, USB may have to be dropped from the project, and another method will have to be devised for programming the user configuration into the EEPROM.
-This is a major disappointment, but I will have to work around it seeing as the hardware has already been finalized.
-
-
-\section{Software}
-
-Software is any program that runs on a host PC, as opposed to on the microcontroller.
-
-I wrote a program called \texttt{usbcom} that communicates with the PIC via USB \cite{usbcom}.
-It connects its standard input to the OUT USB endpoint, and its standard output to the IN USB endpoint.
-It is written in Go, and uses libusb.
-
-\texttt{usbcom} and the PIC firmware communicate using a proprietary text-based protocol over the USB CDC (communications device class) interface.
-The message format is defined using EBNF \cite{protocol}.
-The semantics are a simple request-reply arrangement.
-
-I also wrote a Python script---\texttt{bittiming.py}---to calculate CAN bit timing parameters for the MCP2515 \cite{bittiming_py}.
-
-
-\section{Next steps}
-
-When the board arrives, I will do a visual inspection to ensure that nothing went wrong during manufacturing.
-Then I will solder the THT components in place.
-Once that is done, I will test the board for continuity and shorts.
-With a fully assembled board, I can flash the firmware and migrate system testing from the breadboard to the printed prototype board.
-I will finish developing the rest of the firmware, and run through the full suite of system tests that I will have at that point.
-
-I bought some equipment for testing and debugging the system.
-A USBtin USB/CAN interface will allow me test the reception of CAN frames \cite{usbtin}.
-The EspoTek Labrador is a combined power supply, oscilloscope, and logic analyzer \cite{espotek_labrador}.
-It will be used for powering the board and debugging the SPI lines.
-
-If I have time, I would also like to do some experiments with the power supply to see how it handles changes in input voltage.
-
-
-\printbibliography
-
-\end{document}