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Two Wire Contact Sense With Interrupt

IP.com Disclosure Number: IPCOM000090648D
Original Publication Date: 1969-Jun-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 27K

Publishing Venue

IBM

Related People

Harrison, TJ: AUTHOR

Abstract

This apparatus is for monitoring the status of a plurality of switches using a single pair of wires. The apparatus also provides an interrupt signal for use in an associated process control computer whenever the status of a switch changes. The system utilizes voltage source Vs and reference resistor R located in the control computer. Vs and resistor R are coupled by the pair of wires to the switches S1...Sn whose state is to be sensed. The analog input subsystem is connected to measure the output voltage V between R and ground. Vs is coupled to energize resistors R1...Rn. These are connected in series between Vs and the analog input subsystem with a resistor shunted by the corresponding switch S1...Sn. The values R1...Rn are selected so that the closing of any combination of S1...

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Two Wire Contact Sense With Interrupt

This apparatus is for monitoring the status of a plurality of switches using a single pair of wires. The apparatus also provides an interrupt signal for use in an associated process control computer whenever the status of a switch changes. The system utilizes voltage source Vs and reference resistor R located in the control computer. Vs and resistor R are coupled by the pair of wires to the switches S1...Sn whose state is to be sensed. The analog input subsystem is connected to measure the output voltage V between R and ground. Vs is coupled to energize resistors R1...Rn. These are connected in series between Vs and the analog input subsystem with a resistor shunted by the corresponding switch S1...Sn. The values R1...Rn are selected so that the closing of any combination of S1...Sn produces a unique output voltage V which is measured by the analog input subsystem. Interrupt capability is provided by connecting V to a low-pass filter to provide a delayed output V'. When a switch closes, V and V' differ due to the filter delay. The differential voltage causes the comparator to produce an output which is utilized as the interrupt signal. The switches and the corresponding resistors can be connected as parallel branches or in a series- parallel arrangement such as that commonly used in R-2R ladder networks to provide the same capability. In addition, Vs can be replaced by a current source. Thus, use is made of an analog input su...