doh! Stickduino
That's not the first time I've made that mistake :X
So yes, after staring at it long enough, it hit me that the arduino needs power
I've gotta debug my setup, it's quite messy - and, buggy
It won't always initialize - and when it does, only one character row (bottom) is showing up, and it's displaying repetitive garbage - looks like the duino is resetting. I don't have it hooked up to the obd port just yet.
When it fails to initialize, the hd44780 chip gets hot. Which also happens if I remove my external 12V supply (arduino still powered on over laptop) - BUT, when I do so, I get random pixel flashes on both rows of the LCD o.0
It's late, but I'm thinking it doesn't like having two grounds - 1 being the PC ground to run the arduino and the other being the 12V battery ground. In fact, I'm not entirely sure how I'm getting anything to display - if the three grounds on the LCD are reference voltages, the digital pins from the arduino don't have a "nice" current loop....
Walking away now - I'll save round 2 for tomorrow...