Sequentially operated snap action membrane switches

DETAILED DESCRIPTION In accordance with one embodiment of the present invention, a switching apparatus is provided that efficiently transmits tactile feedback from a snap dome to a person's finger to indicate when a switch has been closed.
The apparatus can also provide a second switch which is closed before the first one but which produces minimal tactile feedback so a person does not erroneously think that the switches have been closed when only the second switch is closed.
The switching apparatus includes an elastomeric keypad with an elastomeric cap having a middle lying above the snap dome which can snap to connect first and second contacts of the first switch.
The keypad includes a coupling portion that mechanically couples the cap to a mount that lies on a circuit board containing the switch contacts, the parts being integral and formed of elastomeric material.
A keycap of rigid material includes a cover lying on the elastomeric cap and a stem projecting down through a hole in the cover and having a lower stem end positioned above the snap dome.
When a person's finger depresses the cover, the stem depresses and snaps the snap dome, with tactile feedback of the snap being transmitted through the rigid material of the stem and cover to the person's finger.
An electrically conductive element is mounted on a radially outer part of the elastomeric cap.
When the rigid cover and elastomeric cap are depressed, the conductive element moves down to engage third and fourth contacts of a second switch to close it.
The second switch is closed prior to the stem snapping the snap dome to close the first switch.
The conductive element is preferably of elastomeric material so that when it engages the third and fourth contacts, very little tactile feedback is created, and most of any tactile feedback is absorbed by the elastomeric cap.
The novel features of the invention are set forth with particularity in the appended claims.
The invention will be best understood from the following description when read in conjunction with the accompanying drawings