Yes, the pictures help. Thanks. You really do need to take several considerations into mind with this kind of project. You expressed an interest to get the engineering part of it right, so you really need to deal with at least these three key issues:
-1- You need to consider whether the data lines can be considered a lumped system (the length is much less than the bandwidth of the transmitted data, both the data bandwidth, and harmonic content on the edges if you are not slew-rate-limiting the waveform), or if you need to treat it as a transmission line. If you run that at 30MHz with sharp XX240 drivers, for sure you will need to treat it as a true transmission line, with impedance control, multi-drop issues, and a valid termination scheme. Even if you run it at 1kHz datarate, the sharp edges on the XX240 driver outputs will generate reflections and ringing on the signals as seen by the receivers.
-2- With a ribbon cable, you really do need to consider the effects of crosstalk on signal integrity. At the very least, the ribbon cable should have the signals ordered: Ground-Signal-Ground-Signal-Ground-etc. That may reduce crosstalk enough, but you will need to look closely at it in the real system.
-3- Putting 0-500mA down the cable will generate ground offsets and ground bounce (when the current draw changes as LEDs are turned on and off). Since you are using a direct-connected datapath (not transformer isolated), the ground reference for the transmitter and the receivers will be different, based on the voltage drop coming back up the ground wire(s) from the current-consuming nodes. This ground shift eats into your DC signal margin, and causes issues with AC signal integrity via ground bounce.
Have you studied transmission lines enough to understand why I am concerned about these things? I work with data transmission line issues every day, and for a system to be reliable, you cannot be cavalier about the issues I've highlited in this thread. For a hobby project for a dance lighting system, where you also have the flexibility to run well below the max datarate supported by the basic components, you may be able to make it work. But for a real product that you design in the future, you will want to understand and manage the TL considerations, or the product will not be reliable in the field.
Ack, I just remembered something else that you mentioned -- I think you are daisy-chaining the serial data line. That's okay, but you will want to back-terminate each line at the driver (the serial output of the LED drive chip). That will keep the receive end from seeing ringing on the line.
