This is not the kind of build I would normally post about here, but it's the only interesting car-related thing I've done in a while, so I thought I'd share the story. Hopefully you enjoy it.
My friend's dad bought his dream car a couple years ago, a 1955 Olds 88. Here it is:
This friend is the biggest gearhead and best wrench-turner I know, and he's modernized his dad's car with an L33 + 4L60e, air conditioning, cruise control; everything it needs to be a comfortable, reliable cruiser for the old man. Since I'm somewhat of an electronics guy, he asked me for help with one of the finishing touches on the project: the gear indicator. The '55 Olds has a hyper-modern electronic gear indicator on the instrument cluster. Here's a picture of another '55 Olds for reference (picture stolen from a random website). It's a beautiful piece of hardware:
Here's what the indicator part looks like outside the car (pictures stolen from an eBay auction):
Wires with ring terminals on those 3 brass lugs energize the coils to move the needle to the desired gear position. I have no idea what mechanism in the '55 Olds controlled the voltage on those wires, but as you might imagine, it isn't compatible with a 4L60e from the mid-2000s.
My friend sent me a description of what the needle on the indicator does when 12V is applied to each lug, and a diagram of which wires on the 4L60e's shifter position switch have 12V on them for each shifter position. Using that information, I generated what is referred to as a truth table in digital logic, with wires 1, 2, 3, and 4 from the 4L60e as inputs, plus R for the reverse light switch as another input, and lugs A, B, and C on the '55 gear indicator as outputs. Here's the info from my friend on the left, and my truth table on the right. In the table, "1" indicates 12V, and "0" indicates no voltage:
Armed with this information, I began writing out equations, drawing gate diagrams, and trying to reduce and simplify them using the techniques from Karnaugh and De Morgan that I learned in college...and eventually gave up and found a piece if software that did a better job in 5 minutes than I did in 2 hours. That software is called Logic Friday, and here's what it spit out for me:
Nice, huh? For the uninitiated, that's 4 NAND gates and 2 NOR gates, easily implemented in a pair of standard logic chips. My friend gave me a few design requirements: he wanted screw terminals for the inputs and outputs, and he wanted 12V from the car to the indicator to be switched by relays. He wasn't sure how much current the coils drew, so he just wanted it overbuilt. I took that and started fumbling around in KiCAD, which seems to be the tool everyone at a hobbyist level uses for circuit board design these days. Once I got the hang of it, I loved it! Way better than the old version of EAGLE I used in college 15 years ago. I ended up with this schematic:
And I was able to design this board from it:
KiCAD has a hella sweet feature that will render your board design in 3D. It didn't have models for all the parts I used, so the screw terminals, relays, and one of the chips are missing, but it's still fun to look at:
There's more to the story, but this first post has already gone on pretty long, so I'm going to stop here and pick it up later. Feel free to throw questions at me in the meantime.
