skewbe -

Have you thought about porting this to a PDA? I noticed in other "data logging" car programs that they would use PDAs.

CarloSW2

This should work fine on PDAs, he made it in Java for the very reason that it should work on almost all platforms and OSes. I'm pretty sure there's full java support on all PDAs and smart phones and that's what most of their applications are made in. You just need to have a line in port on the PDA... which I'm not sure will exist, it should exist on a smartphone or any cellphone for that matter (they all have full Java I think), well microphone input will anyway.

Wouldn't you need to pull infront of and behind the resitor in order to read the drop across it? In fact wouldn't doing it that way cut your max voltage off at whatever can pass through whatever weight the resistor is?

Right now you're pulling from infront of and behind the diode array (which I still don't understand as I don't understand diodes). I will give it a try though.

I had to make compromises because of the common line-in ground between the two signals. There's a lot of variables so If you point me at a schematic for your injectors and vss I will take a look and make a suggestion.

Think of the diode as an open switch until the voltage drop across it is 0.7Volts.
Then it is a closed switch with a constant 0.7V drop.

So it has 2 modes of operation to consider when you read the diagram. The "bridging" is done to garantee it behaves the same independant of the current direction.

A diode is also a "one-way valve" for current, if you don't mind a plumbing analogy...

yay... I just connected mine in my 91 geo metro, 3cyl, and It is working. One thing is not right though. The speed that the program shows is about 5 mph higher than the actual speed on the speedometer. Like if I am going 15mph, the program will show I am going 20 mph. What could be causing this? and how can it be fixed?

Way Cool!! Try this:
locate the mpg.properties file , edit it, and change distanceFudge so it is 20/15 (4/3) larger.

It could be caused by 12 inch tires and other model difference from 92-98 I suppose

I have also noticed that now that I have the circuit wired to the car, I have a check engine light on, and the code 24 shows it to be the speed sensor, even though the speedometer works fine. It goes away when I disconnect the vss from the circuit. I migh make a switch when I make this permanent.

Sounds like input loading by the 10K resistor. Maybe a higher value would fix it? Maybe.