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The Tiny Flip Display

My aim was to build a mechanical display the size of a 1/2" LED 7-segment display. Each of the seven segments has two small neodymium magnets that are offset by 90° and arranged with opposite polarity.

Aranging the magnets perpendicular to the axis does not work, as the magnetic fields influence the segments mutually.

The deflection is achieved by seven inductors with an inductance of 2 mH and a DC resistance of 40 Ohm (Murata LQH43NH222J03L), which are arranged on the underside of the carrier.

The current through the coil is approx. 55 mA, the deflection time approx. 100 ms. Unfortunately, the geometry of the coil cores is unfavorable and ineffective.

The segments are held in their bistable position by reluctance. I use a 74LVC240 buffer/line driver for control, whose ESD protection is sufficient to dispense with additional varistors.

At Vcc = 3.3 V, the output voltage collapses to 2.2 V, so that a series resistor for current limitation can be dispensed with.

Of course, all segments could also be deflected at once, but this would require a different driver.

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