Browse Prior Art Database

Switch Shaper

IP.com Disclosure Number: IPCOM000073827D
Original Publication Date: 1971-Feb-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Laurer, GJ: AUTHOR

Abstract

This circuit conditions a keyboard contact to provide bounce free operation. It also eliminates keying errors due to deliberate opening or remake shortly after a contact or opening, respectively.

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Switch Shaper

This circuit conditions a keyboard contact to provide bounce free operation. It also eliminates keying errors due to deliberate opening or remake shortly after a contact or opening, respectively.

In the normal state switch SW is closed, causing diode D1 to conduct and clamp the base of transistor T1 to ground. With T1 cutoff, the level at the output terminal is high. Diode D2 is therefore forward biased to place transistor T2 in the conductive state.

When switch SW is opened, diode D3 becomes forward biased. The rise in potential at the junction of diode D3-D4 is delayed due to the presence of capacitor C. As capacitor C charges, the potential at this junction rises, causing diode D4 to conduct and bias transistor T1 into conduction.

The turnon of transistor T1 and the attendant down level at the output terminal is delayed a length of time determined by approximately the time constant of R1 and C.

When transistor T1 is in the conductive state, diode D5 is forward biased to reduce the level at the base to transistor T2 below that required to sustain conduction. When transistor T2 cuts off, the voltage at the collector of T2 rises.

The charging current into capacitor C is available to hold diode D4 forward biased and maintain transistor T1 in conduction should switch SW be inadvertently opened shortly after the turnon delay period.

When switch SW is again closed, the base drive through R1 to transistor T1 is removed. The level at the base of transisto...