I'm trying to drive 10x 75HC595 in serie over a distance of 20meters.
I'm using flat cables with 10 conductors.
All goes well for 3-4 units with less than 10meters, but as you might expect, I have transmission errors for more/longer than that.
I'm using a 125KHz SPI clock, but even if I decrease it to 500Hz I keep getting errors, so I guess it is more an EMI issue.
I have 1uF+100nF bypass on all chips, and the output to the bus is driven by transistors in totem pole.
I know the best would be to use a shielded cable and differential signals over twisted pairs...
But I'm trying to find ways I could preserve the signal integrity with the current design. (as bad as it is)
I thought I could make signal repeaters, add caps on the data lines, or sinking/sourcing current to a mid voltage or to a rail...
but that might not be a good idea because of the resistance of the wires...
Any idea on what could be best ?