I am making a wheel encoder out of a Hall Effect sensor with magnets in a concentric circle on the wheel. The Hall effect sensor is on a 2-layer 9x5mm pcb. I usually fill in the layers by drawing a ground shape and then deleting the islands. My question is: should I not add the ground shape because the magnets will induce currents in it- making my circuit unstable? or to put it another way, with magnets passing the pcb, is the less copper the better?

  • \$\begingroup\$ How fast is the wheel spinning? Do you notice any eddy-current braking effects if you held an unetched copper clad board close by? \$\endgroup\$ – Andy aka Sep 23 '13 at 19:24
  • \$\begingroup\$ The wheel has 10 1x.05mm neodymium magnets (1200G) spaced 1mm apart. It turns typically at 300rpm. I could try holding a copper clad board next to it while it spins. I would have to think about how to measure or see braking effects. \$\endgroup\$ – BSEE Sep 24 '13 at 0:04

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