I noticed in the schematic of the Nano ESP32 dev board, that there are three 976kohm resistors in parallel to each color. What is the purpose of these resistors? There are already 499ohm resistors to limit the current in series with the LEDs.
Or capacitors for smoother light with PWM?
My guess is that these are very weak pullups that prevent the LEDs from glowing very, very dimly when the GPIO's they connect to are floating/in high impedance state. These SMD LEDs are so efficient that they'll emit a visible glow (at least in dim lighting conditions) even with the leakage current of a few uA's that will flow through a tri-stated GPIO.
2 Likes
Actually taking a second look, it looks like Arduino actually doesn't populate those 3 resistors. I guess they just act as weak pull up resistors in the case that they choose not to populate the RGB led, maybe for a cheaper version of the board?
Yeah, looks like a measure they took as a precaution and then after some prototype testing decided it wasn't needed, so they left it out. You often see this on commercial PCB's.