CLIAMS:We claim:
1. A method of providing a wetting current to plurality of switches in an input interface circuit, said method comprising:
detecting closing of one of plurality of switches, said plurality of switches are connected to the input interface circuit to provide one of active high input and active low input;
determining mode of operation of the input interface circuit based on the closed one of the plurality of switches, wherein the mode of operation is one of the active high input and the active low input; and
providing a predefined voltage to the input interface circuit by a control unit for generating a wetting current, the wetting current flows through the one of the plurality of switches for a predefined time duration, wherein the wetting current flow is based on the mode of operation of the input interface circuit.

2. The method as claimed in claim 1, wherein detecting of closing of one of plurality of switches and mode of operation of the input interface circuit is determined by the control unit based on the voltage variation in the input interface circuit.

3. The method as claimed in claims 1 and 2, wherein the mode of operation is active high input when the voltage variation is greater than a predefined voltage else the mode of operation is active low input.

4. The method as claimed in claim 1, wherein the control unit provides a low logic voltage from an input port to the input interface circuit for generating the wetting current for the active high input mode of operation.

5. The method as claimed in claim 1, wherein the control unit provides a high logic voltage from the input port to the input interface circuit for generating the wetting current for the active low input mode of operation.

6. The method as claimed in claims 4 or 5, wherein the wetting current burns oxides and other contaminants on contacts of the plurality of switches.

7. The method as claimed in claim 1, wherein the predefined time duration for which the wetting current flows through one of the plurality of switches is 20ms.

8. An input interface circuit system to provide wetting current to plurality of switches, said system comprising:
plurality of switches connected to the input interface circuit to provide one of active high input and active low input;
input interface circuit comprising a voltage source connected across a voltage divider of resistors R1 and R4, connection point of resistors R1 and R4 is connected with a one side of parallel combination of resistor R2 and series combination of zener diode and a resistor R3, wherein one of the plurality of switches providing active high input is connected between other side of parallel combination and positive terminal voltage source, other switch is connected between other side of parallel combination and ground; and
a control unit to control the flow of wetting current through one of the plurality of switches, said control unit is connected to the input interface circuit through an input port, said control is being capable of:
detecting closing of one of plurality of switches;
determining mode of operation of the input interface circuit based on the closed one of the plurality of switches, wherein the mode of operation is one of active high input and active low input; and
providing a predefined voltage to the input interface circuit through the input port for generating a wetting current to pass through the one of the plurality of switches for a predefined time duration to burn OFF accumulated oxides and other contaminates on the one of the plurality of switches.

9. The circuit as claimed in claim 8, wherein plurality of switches are two in number.

10. The circuit as claimed in claim 8, wherein the control unit detects closing of one of plurality of switches and mode of operation based on the voltage variation in the input interface circuit.

11. The circuit as claimed in claim 8, wherein the mode of operation is active high input when the voltage variation is greater than a predefined voltage else the mode of operation is active low input.

12. The circuit as claimed in claim 8, wherein the control unit provides a low logic voltage from an input port to the input interface circuit for generating the wetting current for the active high input mode of operation.

13. The circuit as claimed in claim 8, wherein the control unit provides a high logic voltage from the input port to the input interface circuit for generating the wetting current for the active low input mode of operation.
,TagSPECI:TECHINCAL FIELD
Embodiments of the present disclosure relate to input interfaces providing wetting currents. More particularly, the embodiments relate to universal digital input interface providing wetting current for a programmable duration.

BACKGROUND OF DISCLOSURE
Presently available automotive switching systems that are connected to electronic control units may require a certain current flow when the switch contacts are closed, in order to clean the contacts of any oxidation or other contaminants. This current is referred as wetting current, and may be defined with reference to a particular voltage, for example current greater than 10 mA at 12 volts.

Conventional approach provides a pull-up or pull-down resistor associated with the input processing circuitry in a control unit. The pull-up resistor may be driven by a transistor so that the wetting current may be switched ON or OFF by a control signal connected to the base of the transistor, thereby reducing quiescent current flow. When the switch contacts are closed, power may be dissipated by the pull-up resistor in the form of heat. Therefore, a suitable resistor may be required to be chosen which may dissipate this heat under the worst case conditions, for example at maximum battery voltage and maximum operating temperature. Depending on the application, for example if the circuit is located in a confined space and there are many switch inputs, the heat generated may cause problems with other electrical components. The problems with power dissipation may become even worse in certain systems having 24 volt batteries, because power may be proportional to voltage.

However, it may also be desirable to keep the wetting current at a relatively high level over the contact cleaning period, in order to effectively clean the switch or switches. Also, the conventionally known circuits provide wetting current and are dedicated to only one type of inputs i.e. either active high or active low type of inputs and not for both.

Thus, there is a need of a solution to provide effective universal digital input interface circuit with programmable duration wetting current with minimal complexity. In addition, solution needs to be simple and provide a low cost implementation of programmable duration wetting current using off-the-shelf components for both active high and active low type inputs.

OBJECTIVES OF THE DISCLOSURE
The objective of the present disclosure is to provide a universal digital input interface circuit with programmable duration wetting current and cost effective implementation.

Another objective of the present disclosure is a method of providing programmable duration wetting current in automotive applications.

SUMMARY
The shortcomings of the prior art are overcome and additional advantages are provided through the provision as claimed in the present disclosure.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure.

One embodiment of the disclosure provides a method of providing a wetting current to one of plurality of switches in an input interface circuit. The method comprises detecting closing of one of plurality of switches wherein plurality of switches are connected to the input interface circuit to provide one of active high input and active low input. Also, the method comprises determining mode of operation of the input interface circuit based on the closed one of the plurality of switches. The mode of operation is one of the active high input and the active low input. Further, the method comprises providing a predefined voltage to the input interface circuit by a control unit for generating a wetting current, the wetting current flows through the one of the plurality of switches for predefined time duration. The wetting current flow is based on the mode of operation of the input interface circuit.

One embodiment of the disclosure provides an input interface circuit system comprising plurality of switches connected to the input interface circuit to provide one of active high input and active low input. Also, the system comprises an input interface circuit comprising a voltage source connected across a voltage divider of resistors R1 and R4, connection point of resistors R1 and R4 is connected with a one side of parallel combination of resistor R2 and series combination of zener diode and a resistor R3, wherein one of the plurality of switches providing active high input is connected between other side of parallel combination and positive terminal voltage source, other switch is connected between other side of parallel combination and ground. Further, the system comprises a control unit to control the flow of wetting current through one of the plurality of switches. The control unit is connected to the input interface circuit through an input port is being capable of detecting closing of one of plurality of switches, determining mode of operation of the input interface circuit based on the closed one of the plurality of switches. The mode of operation is one of active high input and active low input and providing a predefined voltage to the input interface circuit through the input port for generating a wetting current to pass through the one of the plurality of switches for a predefined time duration to burn OFF accumulated oxides and other contaminates on the one of the plurality of switches.

The foregoing summary is illustrative only and is not intended to be in any way limiting. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features will become apparent by reference to the drawings and the following detailed description.

BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
The novel features and characteristic of the disclosure are set forth in the appended claims. The disclosure itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying figures. One or more embodiments are now described, by way of example only, with reference to the accompanying figures wherein like reference numerals represent like elements and in which:

Fig 1 shows a digital input interface circuit providing wetting current for both active high and active low inputs, in accordance with an embodiment of the present disclosure.

Fig 2 shows a digital input interface circuit providing wetting current for active high input, in accordance with an embodiment of the present disclosure.

Fig. 3 shows a digital input interface circuit providing wetting current for active low input, in accordance with an embodiment of the present disclosure.

The figures depict embodiments of the disclosure for purposes of illustration only. One skilled in the art will readily recognize from the following description that alternative embodiments of the structures and methods illustrated herein may be employed without departing from the principles of the disclosure described herein.

DETAILED DESCRIPTION
The foregoing has broadly outlined the features and technical advantages of the present disclosure in order that the detailed description of the disclosure that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter which form the subject of the claims of the disclosure. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the disclosure as set forth in the appended claims. The novel features which are believed to be characteristic of the disclosure, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present disclosure.

Referring now to the drawings wherein the drawings are for the purpose of illustrating an exemplary embodiment of the disclosure only, and not for the purpose of limiting the same.

To overcome the drawbacks mentioned in the background, the disclosure provides a universal digital input interface circuit with programmable duration wetting current, which is also a cost effective solution.

An exemplary embodiment of the present disclosure provides a method of providing a wetting current to one of plurality of switches in an input interface circuit. The method comprises detecting closing of one of plurality of switches wherein plurality of switches are connected to the input interface circuit to provide one of active high input and active low input. Also, the method comprises determining mode of operation of the input interface circuit based on the closed one of the plurality of switches. The mode of operation is one of the active high input and the active low input. Further, the method comprises providing a predefined voltage to the input interface circuit by a control unit for generating a wetting current that flows through the one of the plurality of switches for predefined time duration. The wetting current flow is based on the mode of operation of the input interface circuit.

One embodiment of the present disclosure provides an input interface circuit system comprising plurality of switches connected to the input interface circuit to provide one of active high input and active low input. Also, the system comprises an input interface circuit comprising a voltage source connected across a voltage divider of resistors R1 and R4, connection point of resistors R1 and R4 is connected with a one side of parallel combination of resistor R2 and series combination of zener diode and a resistor R3, wherein one of the plurality of switches providing active high input is connected between other side of parallel combination and positive terminal voltage source, other switch is connected between other side of parallel combination and ground. Further, the system comprises a control unit to control the flow of wetting current through one of the plurality of switches. The control unit is connected to the input interface circuit through an input port is being capable of detecting closing of one of plurality of switches, determining mode of operation of the input interface circuit based on the closed one of the plurality of switches. The mode of operation is one of active high input and active low input and providing a predefined voltage to the input interface circuit through the input port for generating a wetting current to pass through the one of the plurality of switches for a predefined time duration to burn OFF accumulated oxides and other contaminates on the one of the plurality of switches.

Figure 1 illustrates a universal digital input interface circuit 100 to interface with both active high and active low type of inputs, in accordance with an embodiment of the present disclosure. The input interface circuit 100 is generally used in automotive applications. The input interface circuit 100 is a universal interface i.e. common circuit for active high or active low at the same time. The input interface circuit 100 also provides higher degree of wetting current pulse for a programmable duration, without imposing continuous power-bleed on the battery. Thereby, the power consumption of the input interface circuit

As shown in the figure 1, the input interface circuit 100 comprises a control unit or a control system or central processing unit (CPU) or microcontroller 102 for controlling the input interface circuit by providing wetting current for predetermined time duration. The input interface circuit 100 comprises a pair of switches SW1 104 and SW2 106 such that only one switch is closed at a time. The switch SW1 104 is closed during active high type of input and the switch SW2 106 is closed during active low type of input.

Also, the input interface circuit 100 comprises a voltage source or a battery 108 providing 8V to 16 V voltage supply, whose positive terminal is connected to a resistor R1 112 and the switch SW1 104. The other terminal of the resistor R1 112 and other side of the switch SW1 are connected with a parallel combination of resistor R2 120, and series combination of zener diode 116 and resistor R3 118. The anode terminal of the zener diode 116 is connected to the resistor R1 112 and cathode terminal of the zener diode 116 is connected to the resistor R3 118. The anode terminal of the zener diode 116 is also connected to a port terminal of the microcontroller 102. The port terminal of the microcontroller acts as an input port as well as output port. Further, the anode terminal of the zener diode is connected to one terminal of a resistor R4 114. The other terminal of the resistor R4 114 is connected to ground 110. In an embodiment, as an example the values of the resistors used in the input interface circuit are R1 is 470K ohms, R2 is 10K ohms, R3 is 330 ohms and R4 is 100K ohms.

In one embodiment, when none of the switches is connected to the input i.e. both the switches SW1 and SW2 are open, the microcontroller 102 analog input reads an intermediate level of voltage in a range of 1.6 to 3.2 volts depending on battery voltage 108. If a switch connected in an active-high manner or mode i.e. SW1 104 is closed, the switch SW1 is shown the figure 1 then the analog input is tied to 5 volts due to internal diode clamp 122 of the microcontroller 102. When the switch SW2 106 is closed or turned ON then the analog input is pulled down to ground 110 providing an active low type of operation in the digital input interface circuit 100.

One embodiment of the present disclosure is providing wetting current during the active high type of input for the universal digital input interface circuit. A circuit 200 during the active high type of input is as shown in figure 2.

As shown in figure 2, when the switch SW1 104 is closed, the microcontroller input port pin 124 is re-configured as an output. Thereafter, a logic low is issued at the port pin 124 of the microcontroller for a time period of 20 milliseconds. When the port pin 124 of the microcontroller is at logic low, the zener diode 116 is reversed and breaks to pump around 20 mA current, when the vehicle or automobile is in running condition. Thereby, a wetting current is pumped into the circuit upon closing of the switch SW1 104 or detecting of the closing of the switch SW1 104, to burn the accumulated oxides and other contaminants on the contacts of the switch, only once after switch ON ignition of the vehicle or the automobile.
During normal operation, due to the power supply 108, voltage across DC bus in the circuit is around 14 Volts, though the resistor R3 118. Thereafter, the input port pin 124 of the microcontroller 102 is restored or configured as an analog input, draining less than 2mA current. The zener diode 116 of the circuit 200 ensures that during normal course i.e. when the switch SW1 104 is on and wetting current is not required, drop across R3 is less than 3V, thereby limiting the current through the switch SW1 104 to less than 2 mA. The current flow through the resistor R3 118 is provided as below in equation 1.

Current through R3 = Voltage across R3
Resistor Value

One embodiment of the present disclosure is providing wetting current during the active low type of input for the universal digital input interface circuit. A circuit 300 during the active low type of input is as shown in figure 3.

As shown in figure 3, when the ignition is turned ON for the first time and the switch SW2 106 is closed, the closing of the switch SW2 106 is detected by the microcontroller 102. The microcontroller 102 input port pin 124 is re-configured as an output. A logic high level is issued at the output for around 20msec by the microcontroller 102, executing the wetting operation, i.e. generating wetting current for burning off oxides and other contaminants on the switch SW2 106 contacts. In the active low type input mode, the zener diode 116 behaves as an ordinary p-n junction diode and the current depends on the resistors R3 118, R2 120 and R4 114. Thereafter, the microcontroller 102 restores the port pin as input port, thereby draining less than 0.1 mA through the resistor R1 112.

The advantages of the universal digital input interface circuit are that the circuit is simple without much complexity in implementation. Also, the implementation cost of the circuit is low. Further, the power consumption of the circuit is low because the wetting current is provided for a predefined time interval only and is controlled by the controller. The operation of providing wetting current to the switches need not be performed very regularly on hourly basis, it can be programmed such that, the operation is performed once in a day or a week.

The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and devices within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity.

In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.