Outline for the Automotive Data Aquisition Project

This page will detail an upcoming project to follow the SeCADA Project. It will implement a similar interface, however, it will be an automotive application. This system, however, will not be a security system, it will simply be a data aquisition project. I will use a computer to monitor fuel consumption, travel rates, and other pertinent automotive data.

The interface will be on the parallel port via a port interface circuit. Thanks to Mike Knowlton for the circuit design. It's a magnetic reed switch that will be placed on the car's driveshaft. The pickup (switch) will be mounted on a bracket directly above the driveshaft, the magnet that switches the pickup will be mounted _on_ the driveshaft. This will allow me to use the parallel port to record the number of rotations of the driveshaft. The number of rotations of the driveshaft will be directly proportional to the number of rotations of the wheels of the car. By calibrating the software and applying the simple formula of: D=RT; (Distance=Rate * Time) I should be able to derive all relevant car statistics.

Some examples:
By knowing the current time, and the distance to travel, the system could use the existing speed (determined from the driveshaft), and predict the estimated time of arrival (ETA). For those long trips to my hometown, Melbourne, this could be a useful piece of information.

By recording the speeds and the amount of gas in the fuel tank, the computer could figure out my miles per gallon (MPG). At the same time, it could calculate the optimum rate of travel for the car. Basically, the exact speed at which the car consumes the least gas.

The system will be able to calculate my quarter-mile time, simply by starting a timer when the car changes from 0 Miles Per Hour and stopping at the 1/4 mile mark. This would be useful in finding the impact of performance upgrades on the car.


Data Aquisition:
Among the data that will be recorded about the cars travels will be the following:

The average rate of travel for each trip. For all intents and purposes a "trip" will consist of when the ignition is turned "on".
The average speed of each trip.
The total distance traveled per trip.
The amount of fuel consumed per trip.
and numerous other items... (to be listed later)

I had originally calculated that the driveshaft turns at most 120 rotations per second. I calculated this at 7000 rpm / 60 seconds / minute= ~120. However, this couldn't be right because the transmission is NOT geared at 1:1 ratio with the engine EVER! So, I'm certain that the system will NEVER have to identify more than 120 revolutions per second.

The hardware will consist of a dedicated microprocessor (probably a cheap 486 or Pentium), and a parallel interface to the driveshaft. The software will be calibrated based on one mile of travel. By recording the number of revolutions of the driveshaft in one mile, I can determine the ratio of the two to each other, and thus the distance traveled at any given time, (assuming no tire slippage).

I may install a soundcard into the computer and connect it to a car stereo amplifier. I'll set up the system to greet the passengers ("Welcome, please fasten safety belts..."), and announce travel status such as excessive speed, etc.

Note:
I haven't evaluated what happens when the car turns. I know that the back tires have a differential that accommodates for different rates of travel at each wheel, but I don't know how (or even if) the software will accomodate for this. I don't think it's necessary, because at least one of the wheels (always the inside wheel), will turn at the correct ratio. After some research (pronounced trigonometry), I'll update this portion of the page.

I'm going to use an optocoupler inline between the driveshaft circuit and the parallel port. This is necessary to protect the computer from spikes and surges that could occur from the quick switching that will occur on the magnet / hall effect sensor.


This is my notebook entry for this project.


Update #1:
I've determined that the pickup needs to be mounted on the rear gearbox of the car so that it will stay in contact the magnet on the driveshaft. I found out that the suspension of the car would cause problems if I mounted the pickup on the undercarriage.

I don't have a name for this project yet, so if anyone has any suggestions, email me.