DEBRA: Digital Emergency Brake Response Alert System Abstract Rear-end collisions on US highways are the single greatest type of traffic accident. This paper describes a stand alone system designed to alert drivers when other cars in close proximity decelerate quickly. The system distinguishes between cars decelerating slowly and quickly. It flashes the center high mounted stop lamp to visually alert following vehicles and also uses an RF transmission to provide audible or other alerts to other vehicles in close proximity. Simultaneously, the DEBRA system also allows for performance monitoring. Using accelerometers, it can measure 0-30, 0-60, ¼ mile, and braking times. Charvak Karpe, Nathan Ackerman 6.111 Final Project May 13, 2004Introduction Background Currently, the single largest type of highway accident is a rear-end crash where one car does not slow down quickly enough and crashes into the rear of another car. Highway rear-ending accidents account for 23% of all accidents and cause almost a million injuries each year in the US alone. When a car applies its brakes, three brake lights illuminate in the rear of the car to alert other cars. Currently, brake lamps only inform other cars of braking and neglect to relay any information on how quickly the car is braking. Often, the cause of the collision is that the following driver does not notice how quickly the car in front is braking. Thus, we believe that rear-end collisions would decrease if there were some warning for when cars decelerate quickly. Goals The primary purpose of the DEBRA system is to enhance highway safety through distinguishing when cars brake quickly. The components required to accomplish the primary goal of DEBRA also allow for monitoring and measurement of car performance with minimal additional overhead. Thus, it is a secondary goal of the DEBRA system to measure car performance using a standard set of performance measuring trials. Overview The DEBRA system alerts other cars when the originating car decelerates quickly by pulsing the center brake lamp instead of leaving it constantly illuminated and also by sending wireless warning signals to other cars. Other drivers will visibly detect the change in the brake lamp. Additionally, other cars equipped with DEBRA will also receive the wireless warning and play an audible warning for the driver as an additional indicator. For measuring performance, cars equipped with a DEBRA system will also contain a LCD display in the cockpit of the car along with a panel for selecting performance testing. Drivers will be able to press a button to start a performance trial and read instructions and results as output from the LCD screen. The overall block diagram of the system can be seen I Figure 1. In addition, there are also a few pieces of physical hardware. Since the main purpose of the project is to design hardware for installation in a car, we had to redesign hardware to be compact. The lab kits typically used for projects were far too large to reasonably fit in a car, thus we relocated all of the parts to a separate PCB which interfaced directly with the power supply and the FPGA. Wireless Transmission In order for cars equipped with DEBRA to send and receive messages, we used the Chipcon CC1010 wireless chip and supported libraries. We used this chip on the supplied CC1010IDE evaluation boards supplied from Chipcon. Using the IDE boards and software provided by Chipcon, we coded a small wireless program and uploaded it to the CC1010. The software utilizes a simple packet protocol (SPP) where all packets contain a destination and source address. In addition, we configured the SPP to send acknowledgement packets back to the sender after a packet was received. If the sender does not receive the acknowledgement packet within the specified window, the sender will continue to resend the packet up to four times before the sender stops trying. Code for the CC1010 module can be found in the appendix.Figure 1: Block diagram of overall system Each CC1010 module waits in receiver mode and listens for packets. When a packet is received, the module switches to transmitter mode to send an acknowledgement. After the acknowledgement is sent, the CC1010 goes back to receiver mode and listens for new packets. At the same time, the CC1010 pulls a data pin high which represents the receipt of a packet from another DEBRA system. This event occurs asynchronously and is sent to the main FSM for processing. Furthermore, when a car wishes to send a packet, a control signal is sent to the CC1010 which tells it to switch into transmitter mode and send a packet. Lastly, all packets are sent out using a broadcast command which does not specify a destination or source address. This is done so that all CC1010 modules, and subsequently, all cars in the range of the DEBRA system will receive the information. LCD controller Users will gauge performance and receive instructions for performance testing through an LCD screen mounted in the cockpit of the car. The LCD is controlled by a Hitachi 44780 standard LCD controller. The 44780 has 14 pins and are assigned as follows in table 1.pins Description 1 GND 2 Vcc 3 Contrast 4 Instruction/register sel 5 Read/write 6 Enable clk 7-14 Data pins Table 1: Pin out for Hitachi 44780 LCD controller In order to use the LCD, data is placed on the data pins and then clocked to the controller. When the enable clock pin goes high, the LCD controller registers the data. To display text on the device, the user must first hold the data steady for 42microseconds. After the hold time, a pulse on enable clock will register the input and if pin 4 is low, a character will be displayed in the first position of the LCD according to a map lookup for the data pins. The cursor will be incremented once so that the next time the same action occurs, a letter will be written next to it instead of replacing it. The FGPA does not directly communicate with the LCD controller. Instead, a PROM is used in between the FGPA and the LCD controller. Since the data is input to the LCD controller in a serial fashion, a PROM is used to stream data from a range of addresses. This technique of using a PROM saves much space in the FSM required to control the LCD screen. For example, it would take a FSM 80 different states to write 40 characters to the LCD screen if a PROM were not used. In contrast, the same 40 characters could be
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