I got my 4-layer board back from OSH Park! This board is different in that I decided to use surface mount components, so I could practice my skills. Before I soldered the components on my new board, I decided to work on a practice board which includes parts down to 0402 size (0.04" x 0.02"). After working with those components, the 0806 size that my board used seemed big!
Here is a picture of the 0402 component (yep, it fits between the "L" and "I" in LIBERTY on a quarter!)
Here is a picture of my final board. I ended up not using Q1-Q4 or R1-R4, I decided that the inputs should just be logic low (of course, I decided that after I already sent the designs to OSH Park.) R9-R11 ended up needing to be 4.7K so that both the LED on the board light AND the relays fully trigger.
The solder paste worked amazing well. I did have two solder bridges, both of which happened to land on pins that needed to be connected together anyways (like U1, pins 4 and 5) but I decided to use a soldering iron to remove the bridges. The circuit handles the 3.3volt inputs and gives 5.0 volt outputs that the relay needs. It also ensures that only one light (Red, Yellow, Green) is on at a time. It has input for the red light of another traffic light (so it can ensure that the cross-traffic has been stopped.)
I think my next goal for the traffic light is to replace the ESP32 (nanoFramework) with a Raspberry Pi (IoT with .NET Core). The board I built should work for either device.
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