I used a SMD rework heatgun to melt the paste and solder the components down. Overall I only dropped about two components out of the ~100 required to complete the watch. Squeezing a component too tightly often led to launching a resistor across the room. A good set of needle (actually sharp) tweezers makes a big difference when trying to move components around. I was forced to use 0402 passive components to get all the necessary components to fit in the layout. Placing the components was quite a challenge. The cathode control lines cover nearly the entire PCB, while the anode control line vias form a wall around the perimeter of the board. A major difficulty in laying out the board was finding areas to place vias between the board layers.
#Pcb anode cathode led square round pad driver
This forms a grid of 15 x 12, which is slightly less than the available outputs for the LED driver chip. Each quadrant gets its own R, G, and B cathode control lines, while four LED chips (one per quadrant) share each anode control line. The face is broken into four quadrants of 15 LED chips. This really forced me into the four layer PCB. The 60 watch face LED chips are electrically arranged in a grid, but they're not mounted in a grid. The layout for this project was very time consuming. KICAD was very intuitive for me, and I was able to start designing after doing a simple tutorial. I figured the PCB would need to be four layers, so this was the best option without having to pay for a license. It's open-source and seemed to have any feature I would need to design the PCB. I decided to use KICAD for my schematic and layout program. This was my first custom PCB in a while aside from some PCBs I've made for various projects in grad-school.
The combination of these LEDs and the driver chip made for a simple control of the watch face. An analog watch face with 60 of these LED chips (one for each minute/second) requires a driver for 180 LEDs. These LED chips have a red, green, and blue LED connected by a common anode. The other component was a 1mm square RGB LED. This chip is an I2C LED matrix driver, capable of driving a grid of 16 by 12 (192!) LEDs. The first was an LED Driver chip, the IS31F元733. At the same time I ran across two components that led to my final design. I wasn't really feeling the design, and decided a mix with a classic analog design would be the best. This led me to come up with a grid of LEDs (5 x 7) for each digit (4 digits: hours and minutes). My first though was to make a digital watch display with a set of the smallest SMD LEDs I could find on digikey. I also needed to be able to purchase or make any of the components. Any design needed to be waterproof, so I eliminated any physical buttons from the concepts. I started by sketching out different concepts for the watch.
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