8 Output (8x 4 Universes)

This is the successor to the 4x 4 Universes pixel board. It is recommended to use this board for all new projects.

In this solution, the SPI is used for outputting the data. The OPi Zero must output the data with 6.4MHz. And the 74-series logic will take care of the WS28xx timing.

What we need is dividing the 1.25 us pulse into 8 time slices. With the above we can finalize that timing circuit with the 74HC161 :  "Presettable synchronous 4-bit binary counter; asynchronous reset". The preset is set to 0b0000.

This results in the following stream:
Logic Analyzer Orange Pi Zero 161 74161 74HC161
The appropriate T0H and T1H can now be generated with comparing the 3-bit counter with the timing values specified in the datasheet. There is no comparator used (there are relative expensive), but instead there is a 8-input multiplexer, the 74HC151.

The 8-input is set by two 75HC595. In such we can set any desired T0H and TH1.
74HC595 Orange Pi Zero 8x 4 Universes pixel board
The 74HC112 is needed for setting the /G when there is SPI output with the WS28xx data.

This results in the following stream for T0H and T1H:
Logic Analyzer Orange Pi Zero 151 74151 74HC151
The 8 outputs are generated by the high-speed 74AHC595. This solution gives a continues output of data when SPI /CS is active low.
74AHC595 Orange Pi Zero 8x 4 Universes pixel board
This results in the following stream for QA..QH:
Logic Analyzer Orange Pi Zero 595 74595 74AHC595
The final output stream is an OR with the T0H and and AND with the T1H. The other input for the OR and AND are the QA..QH.
74HC245 Orange Pi Zero 8x 4 Universes pixel board

With the final RJ-45 connectors.
RJ45 RJ-45 Orange Pi Zero 8x 4 Universes pixel board
The output related to MOSI and T0H/H1H is given below:
Logic Analyzer Orange Pi Zero 245 74HCT245
The output is T1H when the MOSI bit is '1',  otherwise the output is T0H.
Subpages (1): Schematic and board
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