I have a picture of a schematic that has these legends on the resistors. What does N/F stand for? And is it also applicable on other electronic components?
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1\$\begingroup\$ Not fitted, maybe \$\endgroup\$– τεκCommented Jan 17, 2018 at 5:52
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\$\begingroup\$ For completeness: NF with a stated resistance value could also mean that a Non Flammable resistor should go there. \$\endgroup\$– rackandbonemanCommented Jan 17, 2018 at 10:21
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2\$\begingroup\$ It's annoying that there are multiple ways to describe this. N/F, NP, adding a star to the name, etc. \$\endgroup\$– pipeCommented Jan 17, 2018 at 14:44
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\$\begingroup\$ Thanks for all the comments, so would not fitted means that area can be open, i mean put no resistors at all? \$\endgroup\$– MheruianCommented Jan 18, 2018 at 2:44
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2 Answers
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Not fitted. In this case, specifically, the designer wanted to be able to choose whether IN+_2 and IN-_2 should each be connected to either IIN_2A, IIN_2B, or IIN_2C. That's why they used a combination of zero-ohm resistors (which are like wires) and N/F parts.
By selectively mounting zero-ohm resistors to different pads, it allows the designer to reuse the board for different scenarios, or with unknown future configurations.
In the default configuration specified by this schematic, IIN+_2 is directly attached to IIN_2A, and IIN-_2 is directly attached to IIN_2C and IIN_2B.
Because R64 is connected to ground, I assume there was an optional voltage-divider (or digital pull-down) resistor on the design, too.
answered Jan 17, 2018 at 6:12
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\$\begingroup\$ Thanks for all the comments, so would not fitted means that area can be open, i mean put no resistors at all? \$\endgroup\$– MheruianCommented Jan 18, 2018 at 2:44
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\$\begingroup\$ Correct — do not install anything on those pads. \$\endgroup\$ Commented Jan 19, 2018 at 20:33
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Not fitted. Used when you want a footprint on a PCB, but don't necessarily want to install a component there.
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\$\begingroup\$ I see :D thanks a lot, indeed this was very helpful, there are times i see other PCB boards where there are no components soldered at all on some areas, so those are not fitted components. Would that maybe components that should be placed there are for somewhat calibration or testing? settings? configs? \$\endgroup\$– MheruianCommented Jan 18, 2018 at 2:47
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\$\begingroup\$ My guess is economics. It gives the designers options for reconfiguring the circuit without making a new circuit board, and allows using the same circuit board in more than one version of a product. Both save money and time. Parts that are not fitted in production may be fitted for testing and development. \$\endgroup\$– vofaCommented Jan 18, 2018 at 2:55