Making your journey easy to remember

This trip recorder records and displays information about vehicle trips. It keeps track of and displays basic information during a trip such as: starting time, elapsed time, finishing time, distance traveled, average speed, and other trip information. Cost and quantity of gasoline can also be recorded so costs and mileage can be computed.

Information is gathered from the vehicle, processed, and displayed on a liquid crystal display (LCD) panel. Information from a keypad tells the system when to start and stop recording, allows entry of the cost of gas, etc. Information is stored on a plug-in Compact Flash (CF) memory card, a very portable memory media about the size of a pack of matches. This allows easy transfer of the travel information to a PC for record keeping. A low cost CF reader connected to a home PC allows transfer of the data that can be manipulated using a readily available spreadsheet program or word processor.

A Vehicle Speed Sensor (VSS) generates distance pulses as the vehicle travels that are counted by the recorder. The vehicle battery provides power for the system. A signal is supplied to the recorder that indicates that the engine is running. This is so power drain from the vehicle can be minimized when the engine is off.

The recorder consists of a signal conditioning circuitry for the input signals, power conditioning, a processor core, and level shifters for serial I/O. RS-232 serial ports are used to communicate with the display, keypad, and memory card.

Signal conditioning optically isolates the vehicles VSS and Engine Running signals from the processor circuitry. Power conditioning circuitry filters, regulates, and suppresses spikes from the vehicle’s 12-volt power system. Level shifters convert the TTL serial stream to and from the processor to RS232 levels

The processor core consists of a microcontroller and the following support circuitry: RAM, EPROM, a real time clock (RTC), a PAL for glue functions, and a power supervisor chip with a watchdog function. Two UARTs in the microcontroller are used to talk to the external world via RS-232 ports. The RTC is used to keep track of time. A coin battery provides backup power for the RAM and the RTC.

The processor uses time information from the RTC and distance information from the VSS to calculate and display the average speed, current speed and trip times. In this particular application, the VSS is part of the vehicle’s standard speedometer and odometer function.