The vehicle now has 220,000 miles on it. It does not use a drop of oil--and retains over 85 percent of its factory power. Currently, the vehicle is capable of 34-36 mph.
In the meantime, I have been working on an engineering project to design, and build a Vehicle Information Device (VID), that would at least mimic---OBDII in regard to fuel mileage. In some ways the VID provides the essential features of commercial devices like ScanGauge, but for cars older than the model year 1996.
At this stage I have settled on a PIC 18F2520 processor, and worked out the necessary algorithms to measure and/or record fuel usage and distance traveled. I've also developed an efficient method to transmit BCD data to a display board using a two wire interface. The display board can be configured as either an LCD module or a custom seven segment LED display. The LED display is the most interesting as it allows me to mirror the seven segment display and thus create a device capable of being read indirectly from reflection off the windshield. A HUD display--if you will. I use 1 inch seven segment LEDs for this purpose.
The existing VID currently monitors the duty-cycle status of one of four fuel injectors in this car. It also measures VSS (Vehicle Speed Sensor) pulse information. Combining the data allows the device to keep track of the number of gallons used over the distance traveled. It stores this accumulated data in internal flash memory and therefore forms the basics for a vehicle trip computer.
The VID prototype also employs three tactile switches. These switches allow the user to select the type of data displayed. The user can view tank and trip mile per gallon and distance traveled. Currently the display also shows RPM and MPH.The user can use these switches reset trip and/or tank data whenever desired.
The VID also includes an RS-232 interface. This allows the VID to send a constant stream of data to a Windows based program, located on a laptop. The program can be configured to simply monitor and display data, or actually log the data in XML format--for later play back. This feature is useful in analyzing driving styles and locations. I have two windows C# based programs for the laptop. One is a simple graphical/text based program that allows the user to select one of four different data messages and watch the data as it changes. The other program features a nice application of the C#/NET drawing class. It uses bitmaps representations of both the actual vehicle's speedo and tachometer gauges. The application then rotates a bitmap of the pointer and paints it over the gauge display.
Currently the actual device is a 3*3 inch wire wrapped prototype board. Soon i plan to move it toward a PCB prototype as the next step before having multiple PCBs built by a PCB vendor. In the meantime, I am exploring other avenues for simplifying the device design and usage. Currently the device requires the user physically tap into the vehicle's wiring--for power,ground, injector and VSS signals--in what I consider, a rather intrusive way. And, while I don't see any way around taping the fuel injector signal, I am working on ideas to eliminate the need to tap into the VSS. I am also looking for options to eliminate most wiring to the the display Unit. My ultimate goal is to have a device that is battery powered and can be positioned anywhere--including flat on the dashboard--doing this would allow the user to view the mirrored information via the windshield---and thus--- not be accused to being distracted by electronic gadgets. This Heads up Display (HUD) would allow the device to be much more instrumental in assisting the drive with his driving habits.
In my testing so far, the VID device has proven that using the vehicle specifications for the fuel injectors produces realistic fuel use data. (For this engine, the fuel injectors are specified to emit 240 cc/min of 100 percent operation. Or, about 15.48 gallons per hour.) By measuring the real-time fuel injector on time, the device can easily infer the fuel usage to within 5 percent of the actual usage.
Practical use so far shows that by driving the vehicle very carefully around town, the device easily reaches 28-30 MPG. For more extensive drives---covering many more miles, the VID agrees with the numbers arrived by the old method of measuring vehicle mpg.(i.e filling up the tank and driving for n-miles) On a trip of 300 miles or more, the device shows the vehicle average over 34 mpg. Fuel measurement confirms these numbers.
The extensible nature of the PIC/VID architecture will allow it to eventually monitor more vehicle information--- just as OBD does. For instance, the device will eventually provide (4) four, 10 bit analog to digital inputs--useful for monitoring any number of vehicle or environmental data. For example, engine or road temperature, O2 Sensor output, and the like.
So.. please come back for further updates on my efforts to squeeze both more miles and less fuel from my old Honda Accord.
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