I'm now trying to figure out why this is happening:
RPM: Result
at 0: 39Dat 1: 1A1A|RPM Val: 812
RPM: Result
at 0: 39Dat 1: 1A1A|RPM Val: 812
Less than 5 seconds later:
RPM: Result
at 0: B9Dat 1: DBDB|RPM Val: 6843
RPM: Result
at 0: 39Dat 1: 5B5B|RPM Val: 2843
The both results are taken 50ms apart, I don't see how the car has gone from 6000 RPM to 2000 RPM in a mere 50ms. The similarities in the data are also hard to ignore.
I think it's some sort of interference.
Battery Voltage seems stable, 13 - 14 is the readings I get - they are steady - But I think 12V should be there. Either way, it's not 113, so it is believable.
I guess I could test the far more simpler circuit with the 10k resistor from data to ground, and MAX232 to take it from RS232 to TTL!
Any ideas what is up with RPM?