First Sketch - RPI Hat: 2x300 WS2812B LED Strips

[vanepp]

There is a fritzing part for the 74x125 (which is what the ADA1787 is) available here (I think I have been too lazy to submit it to core parts):

74x125 quad tristate buffer

The first in a series of chips that are useful for level translation between 3.3V and 5V (and the other way) systems. This one consists of 4 tristate output buffers in a 14 pin package. Each of the 4 buffers has an input, an output and an enable (active low in this case). Because of this independence this part uses schematic subparts which means you can move any of the 4 buffers around your schematic by clicking on one and dragging it. They are also intentionally small (.2 in wide by .2 high). T…

just download the fzpz file and in Fritzing File->open the .fzbz file will put it in the mine parts bin ready for use. As it stands your circuit is incorrect. The 74x125 is wired incorrectly. Pins 1,2 and 3 look ok (enable on pin1 grounded, input on pin 2, 5V output on 3) but pin13 is the enable and should be on ground, pin 12 should go to the PI as input and 11 (currently unconnected) is the 5V translated output to the LEDs. As well pins 4,5 and 9,10 need to be grounded as CMOS doesn’t like floating inputs. Finishing schematic would be a good bet as it makes problems like this easier to see. Then on to pcb issues. 600 LEDs are likely to want a lot of current and that needs reasonable care. The barrel jack you specified is only rated for 2.5 amps and the LEDs will likely want a lot more than that (the screw connectors are rated at 8A which also may not be enough, the originals are specified to 16 amps). Plan for the maximum current that all LEDs being fully on at once would draw. Don’t believe the “derate the current draw due to multiplexing” suggested on many LED sites as that only works with sync clocks and WS2812Bs have async clocks which will sometimes draw full current, so plan for it. The Fritzing barrel jack footprints have problems as well, I’d suggest replacing the barrel jack with a 2 position terminal block. It supports more current and the wires screw in which is desirable. That said your pcb layout needs much larger trace sizes and shorter routing on the power traces to the LEDs to deal with high current. You will likely get from that many LEDs. The power and ground traces to the 74hct125 should be separate from the high current path to the LEDs to avoid voltage drop issues and the trace width on the high current path want to be as wide as possible (consider using ground fill to use all the copper available) and as short as possible to avoid voltage drop issues.

Peter