How is each LED brightness level varied individually? Are they all able to fade to different colors at the same time or can only 1 be fading at any given time? I see they are connected to two shift registers and there isn't anything connected or being driven by PWM, so I'm not sure how the brightness levels could be varied or a 24 bit color scale could be achieved.
I am talking about the schematic for "Button Pad Controller SPI". I tried to link the URL but it said it had a forbidden word in it.
I am not a beginner to PCB design or coding, but I just don't understand how the varying brightness levels are achieved without an obvious flicker or with any degree of accuracy. It would seem that each column is activated sequentially and the shift registers are updated, but there are only 2 possible states for the outputs of those shift registers - on or off. Is the shift register enable being strobed to achieve varying brightness levels? I would understand if each color was multiplexed and being driven by a PWM which could vary depending on which pixel was selected, but that doesn't seem to be the case here.
The description of this device says it has a 24 bit color scheme like I said before, but I don't see how that is possible. I do understand how each tri-color LED is turned on individually, but what mechanism is controlling the color scale of each individual LED inside each tri-color LED?
One other thing - the duty cycle of each LED is automatically limited to 25% or less it would seem. I would think this severely limits the maximum brightness of each button. Am I correct? This is assuming COLUMNn where n=1 to 4 is being sequentially enabled which is the only way this makes sense to me.