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Conical Return and Capacitive Coupling Spring Keyboard Switch

IP.com Disclosure Number: IPCOM000048236D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Harris, RH: AUTHOR

Abstract

This article describes a conical compression spring utilized as a capacitive coupling member and as a keybutton force return member. Fig. 1 illustrates an exploded semi-pictorial diagram of a single-key position switch. Keybutton 1 is of molded plastic or similar non-conductive material and engages the top coil of the conically wound, round wire helical compression spring 2 upon assembly. The spring 2 is positioned above an enlarged copper pad or similar conductive material 3 which is connected to a source of excitation voltage pulses via copper conductive line 4 placed atop a circuit board substrate of insulated material. An overcoating of dielectric insulation 8 covers the drive line 4 and the circuit board 5 and also covers the sense conductive lines 6. Two apertures in the dielectric 8 are shown at position 7.

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Conical Return and Capacitive Coupling Spring Keyboard Switch

This article describes a conical compression spring utilized as a capacitive coupling member and as a keybutton force return member. Fig. 1 illustrates an exploded semi-pictorial diagram of a single-key position switch. Keybutton 1 is of molded plastic or similar non-conductive material and engages the top coil of the conically wound, round wire helical compression spring 2 upon assembly. The spring 2 is positioned above an enlarged copper pad or similar conductive material 3 which is connected to a source of excitation voltage pulses via copper conductive line 4 placed atop a circuit board substrate of insulated material. An overcoating of dielectric insulation 8 covers the drive line 4 and the circuit board 5 and also covers the sense conductive lines 6. Two apertures in the dielectric 8 are shown at position 7. Through these apertures, solder is applied to join the conical spring 2 to the circuit connections at point 7.

The design shown provides a jumper effect and permits wiring of a keyboard matrix on the single side of a circuit card instead of on two sides. When keybutton 1 is depressed, the spring coils 2 wind down against the dielectric 8 over the drive pad 3 and capacitive coupling between them and the pad 3 increases. As shown in Fig. 2. the capacitance increases in a relatively linear fashion, reaches a knee, and continues to increase in a relatively linear fashion. The force and displaceme...