Can I use a regular 2512 SMD Resistor for the shunt resistor as current sensing resistor for the HLW8012 power meter IC. As per the data schematic, the manufacturer recommend to use a shunt resistor of 0.001 ohms. enter image description here

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    \$\begingroup\$ You can use it - nobody is stopping you but you won't get the accuracy you might desire and there may be nuances you didn't expect due to not using a shunt with kelvin connections. \$\endgroup\$
    – Andy aka
    Jun 12, 2019 at 13:13
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    \$\begingroup\$ The resistance of typical PCB foil (1 ounce/square foot) is 0.000500 ohms per square, any size square. If you are not familiar with thinking about PCB foil resistance, you should use a 4-wire Kelvin resistor for accuracy. \$\endgroup\$ Jun 12, 2019 at 13:28
  • \$\begingroup\$ I presume you are aware the whole circuit must be considered live? (electronics.stackexchange.com/questions/354606/…) \$\endgroup\$
    – Huisman
    Jun 12, 2019 at 13:41
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    \$\begingroup\$ What they said. Note that implementing a really good shunt resistor can involve technologies indistinguishable from magic. You can get thermionic effects, current flowing non linearly in the connections, .... . Much of this does not matter at say 1% accuracy but may well do at better than that. \$\endgroup\$
    – Russell McMahon
    Jun 12, 2019 at 14:01
  • \$\begingroup\$ @Huisman Yes, I'm aware of that but I still don't know what the components connected to GND , Which GND?. Can you explain better to me? \$\endgroup\$
    – Khaalidi
    Jun 14, 2019 at 7:38

2 Answers 2


Indeed you can, at Sonoff they also wanted to save a few cents so they did this:

enter image description here

Image from this site.

Note how the sense wires partly go under the shunt resistor.

Note that if the solder connection isn't good / reliable this can influence the total value of the shunt resistor + solder contacts. That issue is avoided when using a 4-terminal shunt resistor.

Note that at 1 milli ohm, it is easy to get a little extra resistance here and there.

As Andy aka comments: accuracy might be compromised.

Maybe that can (partly) be compensated for by a calibration.

It depends on what your priorities are (accuracy / calibration and cost).


You can approximate a Kelvin connection with a 2 terminal resistor with a custom pad design that allows sensing of the voltage at the electrode of the resistor, rather than the pad of the board. Analog has a good guide to the different approaches you can take - here are some of the possible arrangements that were tested.

Optimize High-Current Sensing Accuracy by Improving Pad Layout of Low-Value Shunt Resistors

The testing showed that trying to measure from a 2 pad arrangement, where the solder resistance is part of the sense element, produces significant errors once you get down to milliohm value shunts.

enter image description here

What is feasible is going to depend on what you can achieve in board resolution and the size of the terminals on the shunt resistor you are using, but a 2512 should allow you to use the following layout, which seems to have an acceptably small error.

enter image description here


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