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N00b here; I have a sensor that I intend to connect to an Atmega 328P (AKA Arduino) running at 5V. I already understand why I need to use a pullup resistor on the active low chip select pin, but the sensor datasheet also suggests taking care with the physical connections and specifically suggests the use of a series resistor between 470 Ohm and 1k Ohm for the MOSI line when using a 328P as an example (obviously chosen for us n00bs). Given the wording, I expect that randomly picking a value in the given range for this one pin will probably not produce the desired results, and I further expect that this has something to do with the current consumption characteristics of the sensor, which are listed as 7mA typical and 8mA maximum.

I'm hoping that some more experienced designers can provide me with guidance here regarding which of the remaining pins (i.e. MISO, SCLK, ~CS) might also require series resistors, and how to calculate the appropriate resistor values (my guess would be to derive the value using a simple application of Ohm's law given the values 5 for the voltage and 0.007 for the current but I'm concerned that it may be more complicated than this). Thanks in advance.

EDIT: sensor datasheet is here: http://www.first-sensor.com/cms/upload/datasheets/DS_Standard-LDE_E_11815.pdf Seems like the info online is different in certain ways from the paper datasheet I have; I'll update this question when I have time to look at the circuit again.

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  • \$\begingroup\$ I suspect it may be to limit current if you have long lines. \$\endgroup\$ – copper.hat Jun 9 '15 at 3:54
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    \$\begingroup\$ Please link to the sensor datasheet. \$\endgroup\$ – corecode Jun 9 '15 at 8:01
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You're not supplying power to the sensor through your SPI lines, so its power consumption is not relevant.
Series resistors in SPI lines are not normal, but could possibly be used for ESD protection if the signals are being routed off the board - in which case the value is not critical.
If you're using really high-speed SPI and your signal lines are very long, then I'd guess its possible that someone might suggest using series termination resistors, but the chances of that are remote, and the resistor values are unlikely to be anywhere near the 470 to 1k ohm range.

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