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Member #145790

Member Since: August 7, 2010

Country: United States

  • 7 issue areas i see

    1) Regulator tab lands are small, i would enlarge and add vias to a bottom plane to distribute any heat. Though current is low as you say, alway make room for a daughter board with higher current requirements. Guaranteed, Murphy will get you here.

    2) Copper flow under Mounting Screws, should add restrict unless they are specifically to carry the GND thru the screw.

    3) BOTTOM Right, via under mounting screw, depending on the screw head type this can be an easy short

    4) BOTTOM Left, resistors are too close to mounting screws, blocked silkscreen and an invitation to screwdrive damage when mounting screws are put in place.

    5) MOSFETs ; these can readily get caught on things, if V1 and V2 leds were shifted between, lay them face down and heatsinking can also me added if future requires. Another approach is mount them underneath and there is better visibility of V1 & V2 leds and since on standoffs still heatsink room. Alternative, with minor movement go to SMD mosfets.

    6) Serial Header; these will break loose very easily, best go to thru pin or at least reenforce the mounting some way.

    7) Tants; as a rule i stay away from Tantalum caps, they come with too many issues. The largest i see is 10uF and these are available in ceramic or Elect.

    Side Note;
    your LD1117 i note are ST's 800mA but have a 1V regulation drop out point. I like Microchip's, it is an identical footprint but has a .2v regulation drop out and in testing i found run a bit cooler under load.

    There aren't any Test Points. Often testing will require verifying the supply voltages and other points. .

  • did it in college 45 years ago and worked.

    to make it work i used;

    • a really good common ground, Stick with common point ground where called for
    • 2 941 OP amps in aliasing configuration with very high impedance input
    • used batteries ONLY not a switching supply, noise is far too high
    • electroplated copper on a 2x3 inch plastic sheet to be thin enough, Tin foil was far too thick.
    • several different magnets.
    • IMPORTANT, calibrate your scope probes
    • keep your connections short as possible
    • my Oscope was an old TechTronics made around 1962 and all vacuum tube for very high impedance.

    A bar magnet worked best due to shape of the field. Field shape and alignment will be critical.

    To get around possible induction I made an adjustable wooden holder (glue only) so the magnet would not be moving and carefully taped down all wires out to 6 inches.

    Once done the OP amp produced a steady offset proportional to the current and the distance of the magnet. Proving changing distance worked. The math from these measure followed Lorentz law as expected.

    As a secondary proof of the field to current ratio; I made a saw tooth oscillator for the current source and you could see the ramp on the scope from the OP amp output. Showing the effect of changing current. My prof really liked that idea.

No public wish lists :(