I’m using the IMP002 which has 2 SPI’s, but the physical LED configuration is 10 seperate strings of LED’s because of the physical distance between them it would have resulted in a data wire length of 90+ meters.
Is there a fast enough demultiplexer that I could use to switch the SPI signal between the different channels (the SPI bus runs at 7500kHz for the WS2812)?
An ideal solution is one that also steps up the voltage from 3.3V to 5V at the same time.
You can definitely switch between strings; one way would be to use (eg) a 3 to 8 line decoder and 8 AND gates - when the 3-8 line decoder drives an output high, that would be used to enable the target AND gate.
You could use level translating AND gates, so you’d also buffer the signals to 5v levels.
eg: 74HCT08 (4x 2 input AND gate, power from 5v, is fine with 3.3v levels). Connect MOSI pin to one leg of each AND gate, and other leg of each AND goes to one of the Yx outputs of a 74HCT238. Inputs on the '238 go to three imp pins.
You then just select the output chain you want to drive with those 3 bits, and send the data.
…this is assuming WS2812’s are ok with idle low. If not you can do similar things with OR gates and a 74HCT138.
YES, for WS2812B can run 7.5KHZ, and SK9822 and APA102 led can run more than 7.5hkz , as they have clock and data , and about the voltage ,the signal is 3.3V , so it is ok .