Browse Prior Art Database

Keyboard Simulator Card

IP.com Disclosure Number: IPCOM000045437D
Original Publication Date: 1983-Mar-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 2 page(s) / 45K

Publishing Venue

IBM

Related People

Jorgenson, G: AUTHOR

Abstract

This article describes a keyboard simulator card which simulates the capacitance for a keyboard at all key positions. It is used with a sense amp card to test the card to see if it will work to the specification of a particular keyboard. The pivot plate down capacitance (to be described hereinafter) is simulated and automatically switched to any drive/sense line combination. The same is true for the pivot plate up capacitance.

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Keyboard Simulator Card

This article describes a keyboard simulator card which simulates the capacitance for a keyboard at all key positions. It is used with a sense amp card to test the card to see if it will work to the specification of a particular keyboard. The pivot plate down capacitance (to be described hereinafter) is simulated and automatically switched to any drive/sense line combination. The same is true for the pivot plate up capacitance.

A capacitive keyboard has its keys located by an electrical matrix. By selecting a drive line and a sense line, one key position can be interrogated. Fig. 1 shows the electrical equivalent circuit and a matrix representation of a capacitive-type keyboard. In Fig. 1, C(D)is the drive to ground stray capacitance. C(S) is the sense-to-ground stray capacitance. The key capacitance, C(C), varies with the key's pivot plate up or down. For a particular type technology keyboard key down (that is, pivot plate down), C(C)=2.8 pf nominal, C(C)=5 pf maximum, C(C)=2.3 pf minimum. For key up (pivot plate up), C(C)=.6 pf maximum, C(C)=.4 pf nominal, C(C)=0 pf minimum.

The simulator card shown in Fig. 2 simulates these capacitances to a sense amp card (not shown). The sense amp card is tested without the use of a keyboard or the simulation of the sense line signals during the sense amp card electrical testing. In Fig. 2, switches S1 through S21 are logical, actuatable reed relays. These relays are actuated by TTL logic circuitry (no...