From b8704d98e828c14682187c71f99a02adad94c321 Mon Sep 17 00:00:00 2001
From: Sam Anthony <sam@samanthony.xyz>
Date: Mon, 8 Dec 2025 16:10:32 -0500
Subject: move proposal and midterm report to doc/

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+\documentclass{article}
+\usepackage{graphicx}
+\usepackage{hyperref}
+\usepackage[backend=biber]{biblatex}
+\usepackage{amsmath}
+
+\addbibresource{../references.bib}
+
+\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 \\
+}
+
+\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}
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