Electronic – Custom LED control module for vehicle

In my opinion, your approach in using this breakout board by sparkfun sounds really good :)

The big advantages are that this board provides 16 PWM channels that are programmable via a daisy chainable serial interface, all led inputs are easily accessible and easy to keep track of.

Also - you probably know already, if you plan on using Arduino, a library that will help you manipulate the driver already exists.

In case you didn't, you should also check out their project home

Since you said that you are pressed I think this solution would allow you to work fast and easy in order to get those leds up and running the way you want them to - Good luck with your project! :)

When using a red and green LED, you can utilize the difference in LED forward voltage as in the circuit below. Make sure to use high efficiency LED's. These have a low internal resistance and a nice and sharp bend in the forward voltage/current curve.

^{simulate this circuit – Schematic created using CircuitLab}

Normally the green LED lights, which has a forward voltage of approximately 2V. Then when the switch closes, the red LED light and due to its lower forward voltage, approx. 1.8V, the green LED will turn off from (voltage) starvation.

If the green LED does not entirely turn off, you can add a regular 1N4148 diode in series with it to make the effect stronger, but this is usually only necessary with cheap and relatively low efficiency LED's.