Browse Prior Art Database

Electronic Keyboard Pivot Plate Status Change Detector

IP.com Disclosure Number: IPCOM000042402D
Original Publication Date: 1984-May-01
Included in the Prior Art Database: 2005-Feb-03
Document File: 2 page(s) / 43K

Publishing Venue

IBM

Related People

Floyd, RE: AUTHOR [+3]

Abstract

The Electronic Keyboard Pivot Plate Status Change Detector facilitates the rapid detection of pivot plate status changes while testing keyboards. The circuit derives its value from its ability to compensate for tester fixtures 12, which have different capacitances for each switch matrix pad card connection pair. The circuit permits each fixture matrix connection circuit to have an equivalent capacitive value from 0 pf to 20 pf. This fixture capacitance must be stable during the period in which its associated keybutton position is being tested. The fundamental element of the circuit is a very stable capacitance excited 1 MHz to 1.5 MHz oscillator 10, whose frequency varies approximately 10 KHz for each 2 pf change in input capacitance.

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Electronic Keyboard Pivot Plate Status Change Detector

The Electronic Keyboard Pivot Plate Status Change Detector facilitates the rapid detection of pivot plate status changes while testing keyboards. The circuit derives its value from its ability to compensate for tester fixtures 12, which have different capacitances for each switch matrix pad card connection pair. The circuit permits each fixture matrix connection circuit to have an equivalent capacitive value from 0 pf to 20 pf. This fixture capacitance must be stable during the period in which its associated keybutton position is being tested. The fundamental element of the circuit is a very stable capacitance excited 1 MHz to
1.5 MHz oscillator 10, whose frequency varies approximately 10 KHz for each 2 pf change in input capacitance. The oscillator 10 is essentially a modified, unbalanced Wien Bridge oscillator with an oscillation start enhancement capacitor. The oscillator's frequency is converted to a proportional DC voltage by frequency-to-voltage (F/V) converter 14. This permits analysis of a broad range of reference frequencies over which a 7 KHz to 12 KHz frequency shift can be detected. At the beginning of each period during which a pivot plate status change is to be detected, a reference circuit 16 generates a voltage value which is sampled and held in sample and hold circuit 18. During the sample period, this reference voltage is compared in difference amplifier 20 to the current voltage representat...