Looking at the waveform of the VSS and Injector Pulses, I'm trying to wrap my mind around what information is being given. I need to do some research if no one knows the answer definately.
VSS
Skewbe claims the VSS only measures distance, requiring the computer to keep track of time. Based on the waveform, it almost looks like it's a "
hand clicker." It seems like he set up a threshold value to determine when the VSS "clicks" (i.e. 9.7V or something).
VSS Waveform Graph
Essentially, it seems like it is counting revolutions. The more "clicks" in a given period of time, the more revolutions, the further you have traveled. Make sense? If so, we need to figure out the distance traveled per revolution and we need to figure out how to deal with variations of that parameter in different cars (unless it's standardized).
Injectors
I believe diesel_john's statement about the 14V, ground to fire, but confirmation from import, other makes would be nice. Skewbe's graph reaffirms diesel_john and he also uses a threshold value to start counting the pulse width. It looks like Skewbe counted the troughs (ground states) rather than the peaks as he did for VSS.
Here is the $1,000,000 question: are all injector pulses the same length (as the VSS pulses seem to be) or do they vary?
Injector Waveform Graph
If they are all the same length then the clicker analogy should do. I doubt that they are. I suppose the length the threshold is tripped needs to be counted.
Arduino
The last area of concern I can think about right now is the arduino's inputs. Apparently we are going to have to use two of the analog inputs (1 for VSS, 1 for Injectors).
The analog inputs only accept up to 5V (@ 10 bit resolution) so a "voltage divider" seems necessary...
According to this forum post, the following schematic would look something along the lines of:
Voltage Divider
Apparently, it needs some more work, but it is just a heads up.
- LostCause