I purchased 2 replacement badges for my 2018 Dodge RAM 1500 recently from LED Innovations. By default they come with two LEDS that can be wired to a single power-source which will activate the LEDs when the vehicle is on. I immediately wondered if I could design a controller that would trigger the lights when the brakes are applied (for the badge on the tailgate) or blink the appropriate 'eye' LED when the turn signals are activated. I wanted to use components I just had laying around (hence some of the component choices) to minimize cost, especially since I didn't know how sucessful I might be. The first decision I made was to use DotStar LEDs for the 'eyes', they're individually addressable and have a full range of color and brightness. The second was to use a NodeMCU ESP2866 board to run the software, mainly because I have a bunch of them laying around. I added a logic level shifter as DotStars are 5v logic and the NodeMCU is 3.3v. I also added a ADS1115 ADC as the NodeMCU only has 1 analog pin and I didn't feel like working through multiplexing. Lastly I needed 4 4N35 optocouplers that act as triggers when a voltage change is detected on the ADC channel connected to one of the input lines (running lights, brakes, left turn signal, right turn signal).
I breadboarded the design and got the software working. Once I knew the circuit was sound I faced the decison on how I was going to wire the whole thing up for an install. I'd thought about just using a proto-board and soldering wires from connection to connection, but that seemed like a lot of extra work ;) A PCB is the answer.