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Diffstat (limited to 'doc')
| -rw-r--r-- | doc/report/report.tex | 59 |
1 files changed, 52 insertions, 7 deletions
diff --git a/doc/report/report.tex b/doc/report/report.tex index fe85a44..c9cda12 100644 --- a/doc/report/report.tex +++ b/doc/report/report.tex @@ -247,7 +247,7 @@ Thus, an 8-bit DAC with 256 steps would have been insufficient, and so a 10-bit The MCP4912 is a dual-channel 10-bit DAC, so two of them are required to drive the board's four analog outputs. -\subsection{Power supply} +\subsection{Power supply} \label{subsection:PowerSupply} Standard automotive electrical systems operate at a nominal voltage of around 13.7V, but can swing between 9 and 16V. The voltage supply often has a strong pulsating component as well, known as ripple. @@ -287,28 +287,28 @@ JCLPCB manufactured the board \cite{jlcpcb}. \begin{figure*} \centering - \includegraphics[width=\textwidth]{"schematic-v0.2.pdf"} + \includegraphics[width=\textwidth]{schematic-v0.2} \caption{Schematic.} \label{fig:Schematic} \end{figure*} \begin{figure} \centering - \includegraphics[width=2.5in]{"pcb_pours-v0.2.pdf"} + \includegraphics[width=2.5in]{pcb_pours-v0.2} \caption{PCB front and back copper pours.} \label{fig:PcbPours} \end{figure} \begin{figure} \centering - \includegraphics[width=2.5in]{"pcb_3d-v0.2.png"} + \includegraphics[width=2.5in]{pcb_3d-v0.2} \caption{3D render of the PCB. Note the vestigial USB-B connector in the top left, to be removed in a future revision (see footnote \ref{foot:Usb}).} \label{fig:Pcb3d} \end{figure} \begin{figure} \centering - \includegraphics[width=2.5in]{"pcb_assembled-v0.2.jpg"} + \includegraphics[width=2.5in]{pcb_assembled-v0.2} \caption{Fully-assembled PCB sitting on 3D-printed stand.} \label{fig:PcbAssembled} \end{figure} @@ -425,7 +425,7 @@ Ideally it should be ported to other operating systems in the future. \subsection{CAN bit timing calculation} \label{subsection:Bittiming} -The second program is a small Python script for calculating CAN bit timing parameters. +The second program is a small script for calculating CAN bit timing parameters. Each node in a CAN network has its own clock generator. The bit timing parameters can be configured individually at each node in order to achieve a common bit rate throughout the network even though the nodes' clock periods may be slightly out of sync. @@ -446,7 +446,52 @@ This can be remedied in a future revision by adding a dedicated 20MHz oscillator \section{Testing} \label{section:Testing} -TODO +A suite of tests was developed to verify the functionality of the device. +Each system test is a standalone firmware image designed to test a particular subsystem. +For example, there are system tests for the CAN, DAC, and EEPROM modules, and for the tachometer and speedometer signal generation systems. +There are also several unit tests to verify some of the more complex routines, such as the CAN decoding functions. +The tests were used continually to check the functionality of each firmware module as they were being developed, and to detect regression as changes were made and new modules added. + + +\subsection{Equipment} \label{subsection:TestEquipment} + +Some special equipment was required for testing. + +A USBtin USB-to-CAN interface enabled reading and writing CAN frames to the bus from a workstation computer \cite{usbtin}. +It was used to monitor the bus during CAN system testing, and to flash the user-calibration onto the device. + +An EpoTek Labrador is an inexpensive all-in-one oscilloscope, signal generator, power supply, and logic analyzer \cite{espotek_labrador}. +It proved invaluable during testing. +The power supply provided 12V to the board. +The logic analyzer was used to debug the SPI (serial peripheral interface) bus while developing the HAL firmware modules. +And the oscilloscope was used to measure the tachometer and speedometer signals generated by the device. + +Finally, a simple multimeter was used for continuity testing to verify the design of the circuit board, and to measure the voltages of the board's analog outputs during system testing. + + +\subsection{Results} \label{subsection:TestResults} + +An issue with the power supply was uncovered while testing the circuit board. +As mentioned in \S\ref{subsection:PowerSupply}, the first stage of the power supply is supposed to output 7V. +However, upon receiving the board, this rail measured only 5V, revealing a mistake in the calulation of the passive components surrounding the buck converter that control its output voltage. +While this issue will have to be corrected in a future revision, it did not prevent the existing board from being used for the remainder of the project. +Bypassing the second stage of the power supply by jumping the 7V and 5V rails, thus providing the ICs with the correct voltage, allowed the board to function well enough. +This workaround can be seen in Fig. \ref{fig:TestSetup}. + +\begin{figure} + \centering + \includegraphics[width=2.5in]{test_setup-v0.2} + \caption{% + Testing setup: EspoTek Labrador (top), USBtin (left), gauge driver (center), PIC programmer (right). + Yellow wire jumps the 7V, 5V-analog, and 5V-digital rails, providing power to the board and circumventing the flaw in the first stage of the power supply.} + \label{fig:TestSetup} +\end{figure} + +Overall, testing has been successful. +Despite minor flaws in the board, the device is able to perform all of its duties. +It is able to receive CAN frames from the bus, decode them, and generate signals to drive up to six analog gauges accordingly. +It can generate two variable-frequency square waves to drive a tachometer and a speedometer, and four 0--5V analog signals to drive four pressure or temperature gauges. +Furthermore, it can be configured for any combination of sensors, gauges, and CAN encoding schemes by flashing a user-calibration with the \emph{cal} program. \section{Conclusion} \label{section:Conclusion} |