Browse Prior Art Database

Electric Circuit

IP.com Disclosure Number: IPCOM000091288D
Original Publication Date: 1967-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 26K

Publishing Venue

IBM

Related People

Taub, DM: AUTHOR

Abstract

Touch keyboards are operated by the capacitance introduced by an operator touching a key. A circuit 1 for use in a touch keyboard system operates a cold cathode discharge tube 2 when the balance of the circuit is upset. This imbalance results when an operator touches point 3, introducing capacitance 4.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 100% of the total text.

Page 1 of 2

Electric Circuit

Touch keyboards are operated by the capacitance introduced by an operator touching a key. A circuit 1 for use in a touch keyboard system operates a cold cathode discharge tube 2 when the balance of the circuit is upset. This imbalance results when an operator touches point 3, introducing capacitance 4.

Circuit 1 includes two signal paths connected between input 5 and capacitor
6. One path consists of resistor 7 and diode 8 connected to pass positive-going signals to charge capacitor 6. The other path contains resistor 9 and diode 10 connected to pass positive signals from capacitor 6 to input 5. A square-wave input is supplied to terminal 5. When the waveform goes positive capacitor 6 is partially charged. When the waveform goes negative, capacitor 6 is discharged. Tube 2 is connected across capacitor 6. It is arranged that the voltage generated across capacitor 6 during this charge-discharge operation is insufficient to trigger the tube.

Capacitor 4, introduced by the operator, is also charged when the input signal goes positive and, until this is discharged, diode 10 is reverse biassed. Thus the charge time is greater than the discharge time and the charge on capacitor 6 builds up until tube 2 fires.

1

Page 2 of 2

2

[This page contains 2 pictures or other non-text objects]