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Is anyone aware of a chip that is capable of detecting the approach (within several inches) of a fairly strong Neodymium magnet (~4000 Gauss):

https://www.digikey.com/product-detail/en/radial-magnet-inc/8193/469-1004-ND/555328

either as a perturbation of the ambient field or as a digital indicator if field strength exceeds a certain threshold?

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    \$\begingroup\$ The Earth's field is much weaker and compasses still work. \$\endgroup\$
    – DKNguyen
    Commented Jul 17, 2020 at 14:16
  • \$\begingroup\$ By 'approach' do you mean movement (how fast?) or static position? \$\endgroup\$
    – Bruce Abbott
    Commented Jul 17, 2020 at 14:22
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    \$\begingroup\$ Search for 9dof IMU modules. Usually 3 degrees of freedom in them are coming from a magnetometer chip. Alternately, just search for magnetometer chips directly. \$\endgroup\$
    – AJN
    Commented Jul 17, 2020 at 14:36
  • \$\begingroup\$ Do you have a reed relay to see if that is activated with that magnet? \$\endgroup\$
    – Andrew Morton
    Commented Jul 17, 2020 at 15:58
  • \$\begingroup\$ Bruce, I mean a slow speed approach (a few inches or so per second). Note the edit to my original post. I've bumped up against another problem in trying to estimate the field strength at different distances along the axis of the cylindrical magnet to see if what I want to do is in the ballpark of a given sensor. The strength of the magnets are rated as "surface gauss". I understand that the inverse square law applies. The problem is choosing a practical "zero distance", since the inverse square goes to infinity at zero. Half height of the cylinder perhaps = "contact"? Thanks all. \$\endgroup\$
    – user1621287
    Commented Jul 17, 2020 at 19:10

1 Answer 1

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That's a darn strong magnetic field. This should be pretty trivial to sense using any kind of magnetic field sensor.

The standard and cheap-as-hell sensor type for magnetic fields is the Hall effect sensor.

To measure movement of that field, you don't even need an IC. A magnetic field moving perpendicularly to a conductor induces a current (basics of electromagnetism!), and at these strengths, you can simply use a trace on your board or a simple wire, and any kind of amplifier to reliably sense this.

Highlights another thing: keep moving strong magnet fields away from your electronics. They induce currents in anything that is meant to conduct electricity.

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  • \$\begingroup\$ Actually, the surface gauss is ten times what I initially said (typo). In using the inverse square law (I2 = I1 * d1^2 / d2^2), I find that at 12 inches distance, the strength has dropped off by 90dB, depending hugely on the distance considered 'zero'. I'm using half the height of a 1/8" tall cylindrical magnet for that. Trying to see if the field at that range is in the ballpark of sensors. I'm trying to reliably sense from below a pet with a magnet attached to its collar. Will keep shielding protection in mind. Thanks. \$\endgroup\$
    – user1621287
    Commented Jul 17, 2020 at 19:23
  • \$\begingroup\$ Great! Yeah, really try hall sensors, and digital signal processing, if you need to detect weak fields that you have a mathematical model for (in how they change over time). \$\endgroup\$
    – Marcus Müller
    Commented Jul 17, 2020 at 19:25

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