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DIY Modular Test Equipment Project
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void_error:
:scared:
I just realized I could simplify some things... maybe... :blah:
And reduce the BOM.
The only thing I have to do is delete the level shifters from wherever they're used and put them on the UI board but there might be some drawbacks...
You won't be able to use modules with different I/O voltages together without an additional level shifter but I won't do that so it's fine with me. :phew:
void_error:
Found another thing I f***ed up badly at. 74HC595 as SPI Chip Select multiplexer. I'll either have to use its reset pin or find a way to interrupt the data flow past it to the other SPI peripherals while shifting data into the 595 preferably using existing connector pins.
void_error:
Problem solved using a 74HC74 configured as a 2-bit Gray code counter since I only have one pin available for latching the 595's outputs. One output goes to 595 latch pin, the other to the reset.
void_error:

--- Quote from: void_error on October 27, 2016, 04:45:36 am ---Problem solved using a 74HC74 configured as a 2-bit Gray code counter since I only have one pin available for latching the 595's outputs. One output goes to 595 latch pin, the other to the reset.

--- End quote ---
Better/simpler idea: divide the 74HC595 latch pulse by 2 and use it as a clock enable to the other SPI peripherals. Only a D-type flip-flop and some gates are required. The reset pin on the 74HC595 won't be needed.
void_error:
Eventually I ended up with a demultiplexer for the SPI clock line.
While looking for parts I ran into these really versatile configurable gates:
http://cache.nxp.com/documents/data_sheet/74LVC1G57.pdf
http://cache.nxp.com/documents/data_sheet/74LVC1G58.pdf
I might actually replace all of the different discrete gates with some of these so there are less part numbers on the BOM.
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