CAN Based Multiplexed Switches Electronics Engineering Technology Department Western Washington University Jordan Mosher 10/19/12
Summary The CAN (Controller Area Network) Based Multiplexed Switches will utilize two can transceivers. The first transceiver will be located in the head unit, while the second will be responsible for a bank of relays. Combined, the transceivers will allow the operator of a vehicle to remotely activate features without the use of overcomplicated harnesses. With the addition of programmable interlocks, a user s input can be checked for errors. If an error is detected, the user input will be rejected and an error message will be displayed. These messages could be due to conflicting features or environmental variables (i.e. speed, rpm, or air pressure). The goal of this device is to remove the possibility of accidental activation and reduce the cost of current switching methods. In the trucking industry, it is common to see over twenty individual switches on the dash of a class 8 truck. By developing a system that would consolidate all of these switches, manufacturers will save time and money. Instead of individually wiring each switch, the user interface could be connected with only four wires, thus saving time. This reduction in wires would also reduce the cost of harnesses, making the addition of features later in the vehicles life simpler. The goal of this project is to build a prototype, which will be focused on the communication and execution of these tasks. Any spare time will be used to develop the user interface or vehicle emulator. 1
Description The final package size will be larger than a production module, due to the nature of a prototype. The display will fit into a double din slot, which is common in the automotive industry. While the relay bank will remain small enough to be mounted on a firewall or frame rail. The main goal of this project will be to establish a CAN Network using the TI Stellaris LM4F120 LaunchPad Evaluation Board. Once this network is established, it will be utilized to carry switching information. This will be accomplished as follows. Phase 1) One Stellaris will be responsible for user input, keeping track of the switches and their indication lights. When switches are activated this board will also provide the user with information on a LCD. Lastly, when a switch signal is confirmed, the board will then send out the corresponding CAN message. The second Stellaris, responsible for a small bank of relays, will then receive the confirmed switch statements via the CAN bus. Based on this statement, it will turn on the corresponding relays. There are several goals for this project beyond establishing a CAN Network. If time permits, additional features will be added in the order that follows. Phase 2) Make it possible for the relay bank controller to respond with current positions of all the relays. This would allow detection of a faulty relay without manual testing of the system. 2
Phase 3) Add a third Stellaris to the network, responsible for emulating a vehicle CAN bus. This emulator would output information such as vehicle speed, engine RPM and system air pressure. Allowing the demonstration of interlocks that are based on these parameters. Phase 4) Incorporate a touch screen display using an Android tablet and IOIO. IOIO (pronounced yo-yo) is a USB interface that can be attached to Android devices allowing digital output. The tablet will provide the platform to run a custom app that will be designed for this project. Phase 5) Add diagnostics. Have a self-testing and diagnostics feature for the system. This would allow for quick and easy replacement of parts that were defective. If a fuse or a relay went out the user interface would tell a mechanic what part of the system was not functioning and advise testing. Phase 6) Backup fuse and relay for safety system. Headlights and electric over air systems have an extra relay and fuse that can be activated in the case of a failure. This could also be turned on in situations where extra current is necessary. Cost Estimate: Stellaris x 4 Switches x 6 Relay x 10 fuses Enclosure Stellaris x 2 (Optional) Tablet (Optional) IOIO (Optional) Total Parts(in Dollars) $30.00 $15.00 $30.00 $20.00 $50.00 $10.00 $100.00 $55.00 $310.00 Time ($100/hr.) $4,000.00 $100.00 $300.00 $300.00 $300.00 $2,000.00 $4,000.00 $400.00 $11,400.00 Use of Time Programing mounting PCB PCB Manufacturing Programing Programing Integration Background Currently, companies like Eaton offer some multiplexed switch options for the heavy truck industry. But at this point, none of these companies have developed 3
a system that would reduce the number of components and manufacturing cost in the way that this project will attempt. Freightliner has recently come out with their new multiplexed wiring that they are calling the M2. This system, although a step in the right direction, does not reduce complexity and cost of their system. In the M2 system, each individual switch has its own CAN transceiver. These features result in wiring that has not been significantly decreased and costs that have increased. The configuration being developed for this project will not just save costs on the harness and hardware, but will also help prevent accidental activation of components with the use of software interlocks. By monitoring the trucks communication network, it is possible to check information such as vehicle speed and engine rpm. With this information, a micro controller such as the LM4F120 is capable of deciding whether user input is possible and/or responsible. Societal Impacts In a study completed by the DOT and NHTSA s (National Center for Statistics and Analysis), over one hundred and forty thousand truck accidents were examined from 2001 to 2003. In this study it was found that twenty-six percent of the accidents caused were due to driver error. With the use of software interlocks, potentially fatal mistakes can be caught and corrected which in turn will save lives and thousands of dollars in damages per accident. This system does not have to be limited to electrical components. With electric-over-air switches becoming more popular in the heavy truck industry, replacing a relay with one of these air switches 4
would provide control over a vast majority of the features on a truck. Features like fifth wheel disconnect or trans axle lock could have interlocks that prevent their use at high speeds. By creating a system that allows for expansion, the cost of upgrading or adding features can also be reduced. With this advancement, upgrading safety and emissions features could be done in the future with out the hassle of rewiring a truck. This would also reduce the cost of these upgrades, making them more cost effective for drivers as well as fleet owners. With reduced cost, we would see many trucks upgrading to the latest features, creating a safer roadway for everyone. Project Development The project will be developed over the course of the next seven months and will require no additional funding from the electrical engineering department. Using the Stalaris LM4F120, a board that has just been released, will defiantly result in some complications. But, TI (Texas Instruments) has a good reputation for supplying numerous examples and great documentation for their boards. In addition to this, I am currently taking DSP (Digital Signal Processing), which utilizes another board that was developed by TI. Lastly, many students in the EET program are planning to use this board for their projects. All these factors will help reduce the likelihood of failure due to board complications. 5
Although this project will not be focusing on the user interface, the LCD display will be used as an effective debugging tool, along with LED indicators mounted in parallel with the relays. For the sake of debugging, an LCD display may be added to the truck emulator to display the current speed, RPM and system psi. In order to demonstrate this system, there will not be any high current loads. Instead, LED indicators will be turned on when each relay is active. By removing any high current loads from the demonstration there will be no need for a large power supply or battery. The display for this project will consist of three parts. The user interface will be interactive so that people attending the presentations will be able to cycle switches to see the results. Second, if time allows, the truck emulator will allow individuals to change the speed, RPM and system psi of the truck. Effectively demonstrating the interlocks that will be programmed into the system. Lastly, a relay bank will use a set of LEDs to display the status of each really. All together, these components will display my knowledge of the CAN protocol while incorporating my extensive automotive background. Timeline: Nov. Dec. Jan. Feb. March April May Projec Proposal Order Parts Final Project Discription Get Boards Set up CAN Communication Phase 1: Messages Between Boards Build display Continue Working On Software Deal With Unexpected Setbacks Work On Extra Features Prepare Hardware Schematics Hardware discription Finish The Programing Code review 6