The document summarizes the design of a handheld OBD-II reader device that connects to a vehicle's onboard diagnostic port to read error codes. It uses a PIC32 microprocessor and touchscreen LCD to interface with the CAN-bus and communicate with the engine control unit. The design process involved selecting components, designing circuits and layout, and fabricating a printed circuit board. Challenges included touchscreen communication, design errors, power issues, and CAN message transfer.

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The CAN (Controller Area Network ) Device OBD-II (On Board Diagnostic) reader
is a handheld touch screen computer that interfaces with an automobiles OBD-II
port and reads the basic SAE (Society of Automotive Engineers) codes from the
ECU (Engine Control Unit) through the CAN-bus as shown in Figure 1. The CAN
Device uses a PIC 32 microprocessor to communicate with touch screen LCD. A
PCB was designed and fabricated to have all parts mounted in one small package.
Modern vehicles have many computers to control the advanced systems such as
brakes, power steering, transmission, etc. The CAN-bus was created as a
communication system to allow all of the vehicle’s subsystems to communicate
simultaneously. All modules communicate simultaneously with the main ECU
therefore a priority system is necessary to give priority to important messages. It is
one of five communication protocols used on the OBD-II standard and has become
mandatory to use on all vehicles 2008 or newer in the U.S.
Introduction and Theory of Operation
The first step was selecting the Kyocera display; chosen for its price, functionality
(display and touchpad all in one), and its ease of programmability. Next the
Microchip PIC32 microprocessor was chosen for its processing power and its
compatibility with CAN. It has a dedicated module specifically for sending,
receiving, and storing CAN messages with only a CAN transceiver needed to
complete the communication. Once the main components were chosen, the next
step was configuring power distribution. Three different voltages are necessary to
power all the components: 3.3V to power the processor, display and touchpad, 5V
to power the CAN transceiver, and 19V to power the LED backlight of the display.
Because the CAN device interfaces with the ECU it was decided that the power will
be drawn from the car battery (12V-15V). A 9-36V to 5V switching converter was
chosen to step the voltage down to 5V to maximize efficiency. From there a linear
regulator is used to step 5V down to 3.3V, and a boost converter is used to step it
up to 20V.
Design Process
Communication protocols
There were several different modes of communication used within the CAN Device
including parallel data transfer, synchronous serial data transfer, and asynchronous
serial data transfer. The LCD part of the display uses a 16bit data bus with read
(RD), write (WR), register select (RS), and chip select (CS) lines. [2] The touchpad
part of the display uses a serial peripheral interface (SPI) to communicate data in
and out. The SPI interface only has one line to carry the data in (SDI) and one line
to carry the data out (SDO) The PIC32’s CAN module acts as a controller on the
CAN-bus allowing it to send and receive messages to and from the bus. The CAN
transceiver converts the serial data from the microprocessor to the differential
(CAN high and CAN Low) signals. Each message has a unique 29 bit identifier to
identify what type of data it is and between 8 to 64 bits of data in the message. [4]
Figure 4 shows what a typical CAN network looks like.
References
Tony Sossong and Zach Stambuck
CAN Device OBD-II Reader
Implementing the Design
A schematic was created using ORCAD Capture as shown in Figure 2. Next the
PCB layout was implemented on PCB editor as shown in Figure 3. Figure 5 shows
the milled PCB. There were many critical elements that went into the PCB design,
the most critical aspect of the layout being the placement of the display ribbon
connectors with respect to the screen mounting holes. Incorrect measurements
would prevent the ribbons from aligning, which would prevent the screen from being
able to be connected.
Results/ Challenges
Environmental and Economic Aspects
Overall the project ended as a success. Figure 6 shows what communication
between the processor and the touch pad looks like. Getting the touch screen to
communicate with the processor was one of many challenges presented. Other
challenges include PCB design errors, power issues and CAN message transfer/
receive issues. Designing the PCB layout was by far the most time consuming
challenge. Routing lines efficiently and minimizing data line lengths for optimal
performance caused extreme attention to detail in the design process. The PCB
sizing is not optimal due to not possessing the LCD touch screen until after
designing the PCB therefore it is larger than desired but about average in size
when compared to market competitors.
The CAN device gives an extended window into the statuses of critical systems of
a vehicle that are not known or accessible to a standard driver. Because it is not
critical to the average customer, the CAN device would be a great item for
hobbyists who like to tune engine parameters or repair technicians who want a
pocket reader. The CAN device has some advantages and disadvantages
compared to similar products. One advantage is the touch screen capability in
small design. Many of the full graphics display CAN readers are 2-3x larger than
the CAN device. Even though it is smaller than most, the design could be further
refined to make it smaller and more pocket friendly. [5]
Figure 2: OBD-II Schematic
Figure 3: PCB Layout
Figure 6: SPI Communication with Touch Pad
Figure 1: CAN Device in Operation
Figure 5: Milled PCB
[1] Microchip, “PIC32MZ Embedded Connectivity (EC) Family Data,” PIC32MZ2048ECH144 datasheet, Feb. 2013 [Revised Nov. 2013].
[2] Renesas, “RGB Graphics Liquid Crystal Controller Driver,” R61509 datasheet, Mar. 2006 [Revised Nov. 2007].
[3] Analog Devices, “CapTouch Programmable Controller for Single-Electrode Capacitance Sensors,” AD1747 datasheet, Sept. 2007 [Revised Jan. 2015].
[4] Microchip, “PIC32 Reference Manual,” Section 34. Controller Area Network (CAN), Jul. 2009 [Revised May. 2012].
[5] T. Sossong and Z. Stambuck, “CAN Device ABET Engineering Economics Report,” University of Arkansas Senior Design Laboratory, Fayetteville AR. 17 March, 2016.Figure 4: Typical CAN Network [4]