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Touch Button Circuit

IP.com Disclosure Number: IPCOM000094230D
Original Publication Date: 1966-Jul-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Taub, DM: AUTHOR

Abstract

The touch button circuit operates from a low voltage pulse supply and a DC supply sufficient to cause a gas trigger tube T to strike. Tube T has its trigger electrode biased by a bias network including resistors R2 and R3. In the absence of any external signal T just fails to strike. Connected to the junction of R2 and R3 is capacitor C2 charged by pulses from a pulse train P by way of the emitter-collector path of V. The base of V is connected to the emitter through resistor R1 and also to the plate of touch button B.

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Touch Button Circuit

The touch button circuit operates from a low voltage pulse supply and a DC supply sufficient to cause a gas trigger tube T to strike. Tube T has its trigger electrode biased by a bias network including resistors R2 and R3. In the absence of any external signal T just fails to strike. Connected to the junction of R2 and R3 is capacitor C2 charged by pulses from a pulse train P by way of the emitter-collector path of V. The base of V is connected to the emitter through resistor R1 and also to the plate of touch button B.

The placing of a finger on the touch button causes a capacitance to be established between B and earth. This capacitances referenced C1. When C1 is absent, both base and emitter of V are at the same potential and no collector current flows. Tube T thus remains biased slightly below its striking voltage. When, however, C1 is present, it charges through R1 during each negative going pulse. C1 discharges through the base-emitter junction of V in the intervals between the pulses. This causes pulses of collector current to flow, charging C2 to a higher voltage on each successive cycle. Such occurs until the voltage at the junction of R2 and R3 is high enough to fire T.

It may happen that the collector-base capacitance of V causes an unwanted output signal to be delivered. When the emitter potential of V changes from its maximum negative value to zero in the absence of C1, the charge on the collector-base capacitance Ccb changes by VpCcb. Vp is the absolute magnitude of the negative-going pulse. Ignoring the current flowing through R1, this means that an equal charge is bu...