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Comment by Faaak | Hacker News Reader

A thing that I really miss in Kicad is the ability to quickly add zero-ohm resistors when editing the PCB layout while not modifying the schematic. Indeed, when you do your own boards in house, it's really convenient to add a zero-ohm smd resistor for jumping over a trace, without having the need to go and edit the schematic..

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You can just create a PCB with one additional layer and use that layer (top one for example if you make single-sided pcbs at home) for jumpers, then to add a jumper while routing a trace, switch layers, which will add a through-hole via, trace your jumper, then jump back to the initial layer through another via. When etching the board you omit that layer and later solder wires where the traces were.

It's quite flexible as you can add jumpers of any length and orientation that way, the only inconvenient is that jumpers aren't marked on the silkscreen but it's fine for home-made projects.

This is the correct-ish way if you don't plan to actually populate zero-ohm resistors from a BOM.

But then your BOM, PCB, and schematic wouldn't match. Somewhat like automatic code formatting, disallowing this sort of divergence seems more a feature than a misfeature to me. Even for in-house use.

Some bit of my head is a zero ohm resistor resistor. Every time I read 'zero ohm resistor', it goes 'nope nope nope' at me.

It's zero in the number of significant figures used by the test equipment.

That's a pity because then you can't use that resistor to measure current by a measurement of a voltage difference.

They make high-precision low-resistance resistors specifically for current measurement. Your standard cheapo zero-ohm resistor though is more for creating optional connections that you can configure at assembly time.

Think of it as an "epsilon ohm resistor".

My 1/4W THT zero ohm resistors are about 0.025 ohms according to my bench meter. In theory, that implies a 400 amp rating... not going to try that anytime soon :)

Heh, I like that. I tend to think of them as a surface mount jumper.

Why not? They're great as test points and you can pull them off and place a resistor or capacitor in their place.

I assume it's the paradox of a resistor that doesn't resist.

Probably because the operating temperature is about 0 Kelvin.

I guess it doesn't have to go quite that low, depending on what you make it out of.

Though you have got me wondering whether anyone has put a crumb of high temp superconductor in a smd resistor package yet and if so, for what purpose.

"High temperature" is relative, they still have to be cryogenically cooled to temperatures around -100C. So no SMD superconductors yet.

That is still a relatively accessible temperature, given that liquid nitrogen is about the same price as clean water.

Off the top of my head, I could think of one use, which would be to trigger a transistor to switch on and off some high power superconducting circuit when the small bit of superconductor gets cold enough to start superconducting.

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