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I'm working on a project where I need to sense if a circuit is in operation on a wide range of vehicles. My plan so far is a current sensing clamp, and an Arduino micro listening for the current draw on that wire to be above 0ma. (or a more reasonable threshold to be determined)

I've looked into the normal clamp meters for AC applications, but they dont work on DC. I also need this to be non invasive, and able to be quickly attached to and from various wires - so must be a split loop pickup or similar... These types of current sensors wont work, as they are invasive.

I'm thinking some kind of a coil on an Arduino analog input, that is clipped onto the wire to monitor - but I'm at a loss as to what this coil needs to look like - and I'm not getting anywhere trying various random coils hooked up to an Arduino and looking for any change in analog read...

Can anyone offer any help on this?

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  • \$\begingroup\$ Forgot to mention in the post - this is intended to be eventually made into a production run of sensors for vehicles, so the intent is to scale it up not just build a one off device. \$\endgroup\$ – Taylor Oct 4 '18 at 3:34
  • \$\begingroup\$ You'll need to explain what the wire does, and especially the magnitude of current carried. Magnetically coupled DC sensing of moderate currents is possible for example via the hall effect, but works best when the current to be measured is routed through the measuring device (for example ACS712 style) and not merely clamped on. Could you maybe extract the information you need from the ODB port? \$\endgroup\$ – Chris Stratton Oct 4 '18 at 5:15
  • \$\begingroup\$ In case it helps some, also look up asymmetric magneto-resistance and spin-transfer torque. \$\endgroup\$ – jonk Oct 4 '18 at 6:06
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    \$\begingroup\$ Gave a correct answer to the original question before clarification and get downvoted, gets to the point that can't be bothered... \$\endgroup\$ – Solar Mike Oct 4 '18 at 7:40
  • \$\begingroup\$ @SolarMike - I didn't downvote your response, but I did think about it. This is an engineering site, and a question about sensing technologies was asked. Your response was to indicate that a tool vendor sold an instrument (not a sensor) that did something like this. That's not an engineering answer about sensing technology - it's not even a "link only" answer. At most it was a comment to prompt research by the asker. \$\endgroup\$ – Chris Stratton Oct 4 '18 at 15:39
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NVE corp makes GMR (Giant Magnetoresistance) based sensor ICs that can non-invasively sense the current in a wire that is in close proximity to the chip. Usually they sense a PCB trace running under the chip, but you could perhaps make a PCB with a slot under the IC and clamp the wire into the slot.

They even have a video app note for using their AAL024 sensor with the Arduino.

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  • \$\begingroup\$ This looks amazing - Ordering a few bits from them now - exactly what I hoped existed. Thank you VERY much! \$\endgroup\$ – Taylor Oct 4 '18 at 22:12
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These do exist, I've used them before. The name of the device you're looking for is a "DC current transducer". Well at least that's what they call them industrially.

http://www.crmagnetics.com/dc-current-transducers/cr5211s

An over-the-trace hall effect current sensor might work for you. Although these are usually used for currents in the 10A+ range, it may be possible to make it work.

https://www.melexis.com/en/product/MLX91205/90kHz-IMC-Hall-Current-Sensor

If that doesn't work, you may have to start making your own sensor.

https://en.wikipedia.org/wiki/Hall_effect#Ferrite_toroid_Hall_effect_current_transducer

I won't go into too much detail, but basically if you cut a ferrite and put a hall effect sensor in the gap that will act as a current sensor. I think it would work fine with 2 gaps too, which would allow it to be clamped on.

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