Given that the Design Report was due this week, we had to lock in a lot of the details that we were uncertain about up until now. The process of writing the report was very helpful and made us think critically about the more challenging parts of our project. Up until this week, we had assumed that we would be using addressable LEDs to represent our traffic light mockup circuit, but when I was doing research on this type of LED I realized that most available ones can draw up to 60 mA of current per LED. Since we will be using an Arduino to control the light timings, and an Arduino’s digital GPIO pins can only output a maximum of 40 mA of current (and 20 mA of constant current) without causing damage to the hardware, this was not going to be a feasible solution. Therefore I made the design decision to instead have the Arduino drive a Texas Instruments TLC5928 LED Driver module which can output a constant current to up to 16 different LEDs by setting a reference current by tying an apt resistor to the module’s V_CC pin. This will allow us to draw power from the Arduino’s 5V output pin, which can supply up to 900mA of current, instead of the individual GPIO pins. The GPIO pins will instead drive the logic at the input pins of the LED Driver module. All 12 LEDs that will represent our traffic light circuit as well as the LED Driver module will be soldered to our custom breakout PCB for the Arduino so that our physical intersection simulation can all be integrated into one place. The schematic mockup I created in Eeschema for this circuit is below.

My plan for the next week is to get the necessary parts ordered and learn the protocol for the TLC5928 unit’s input logic so that I can write Arduino code to drive our LEDs. I would also ideally like to have our PCB layout completed, but we will wait to order it until the LED Driver module comes in so that I can test that everything is working as intended before we get our PCBs printed.