I'm using the MCP4131 digital potentiometer to control the brightness of a LED using an Arduino Uno. The MCP4131's interface is SPI and it has a multiplexed SDI/SDO pin (pin #3).

The datasheet specifies a resistor R1 to be placed on the host's SDO before the host SDI/SDO signal are being multiplexed. I was wondering how to calculate it's value? For now, I used a 1k resistor and it works but I want to learn how to deduce this value from the datasheet.

The comment says that R1 must be sized to ensure VIL and VIH of the devices are met, I can't figure out what these are.

If anyone can explain I'll appreciate it, thank!

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  • \$\begingroup\$ You need to check comment 2, which says "R1 must be sized to ensure VIL and VIH of the devices are met". If you need help with this bit then perhaps adjust your question. \$\endgroup\$ – David Nov 16 '13 at 11:16
  • \$\begingroup\$ Yeah thanks, I modified the question as you suggested. \$\endgroup\$ – GetLastError Nov 16 '13 at 16:16

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