Communications: electrical – Audible indication – Percussion-type sound producer
Patent
1984-12-24
1987-03-17
Caldwell, Sr., John W.
Communications: electrical
Audible indication
Percussion-type sound producer
340365R, 340365S, G06F 302
Patent
active
046511334
ABSTRACT:
A capacitive keypad (24) is scanned in such a manner that the capacitance value (C) of an individual key in a given row is multiplied by the sum of the relative capacitance values of all the other keys in the same row by means of an amplifier (32) to generate a combined pulse. The combined pulse is then compared by a comparator (28) to a threshold voltage (Vref 3) to verify whether the individual key in question is in the closed or open position. The verification can be made independently of keypad-to-keypad variations in the capacitances of the keys, since the combined pulse value does not depend upon the absolute capacitance value of the keys, but only upon their relative values. Also disclosed is a method for scanning to determine the presence of multiple key closures. This involves comparing the capacitance of an interrogated key to not only the sum of the other capacitors of its row, but also to the sum of the capacitors of the other rows and columns and a comparison of the resulting value to that generated by previous scans to detect change.
REFERENCES:
patent: T904008 (1972-11-01), Crouse
patent: 4211915 (1980-07-01), Miller
patent: 4305135 (1981-12-01), Dahl
patent: 4405917 (1983-09-01), Chai
patent: 4405918 (1983-09-01), Wall et al.
patent: 4414538 (1983-11-01), Schnizlein
patent: 4539554 (1985-09-01), Jarvis et al.
"Capacitive Keyboard FET Sense Circuit", IBM Technical Disclosure Bulletin, E. G. Crabtree, J. M. Sublette and D. R. Thomas, vol. 24, No. 5, Oct. 1981, pp. 2237-2240.
"Matrix Scanning Logic for a Capacitive Switching Keyboard", Computer Design (USA), John W. Volpe, vol. 12, No. 1, Jan. 1973, pp. 84-88.
Ganesan Apparajan
Weise Wayne A.
AT&T - Technologies, Inc.
Caldwell Sr. John W.
Fatahi-Yar Mahmoud
Ulbrich Volker R.
LandOfFree
Method and apparatus for capacitive keyboard scanning does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for capacitive keyboard scanning, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for capacitive keyboard scanning will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1790819