FORM 2
THE PATENT ACT, 1970 (39 OF 1970)
AND THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See Section 10; Rule 13)
METHOD FOR DETERMINING POSITION OF INDEXED POTENTIOMETER AND APPARATUS THEREOF
SELEC CONTROLS PVT.LTD.
an Indian Company
of Plot No. EL -27/1, Electronic Zone, TTC Industrial Area,
MIDC, Mahape, Navi Mumbai 400710,
Maharashtra, India
Inventor: KAJI SAM IR
The following specification particularly describes the invention and the manner in which it is to
be performed.

TECHNICAL FIELD OF INVENTION
The present invention broadly relates to uses of a potentiometer. In particular, the present invention relates to a method for accurately determining positioning of a potentiometer and an apparatus thereof.
BACKGROUND OF THE INVENTION
Very commonly used electrical devices have one or more controllable functions such as volume, brightness, mode, time, speed, and the like, wherein, the user can select a value for a function, thereby controlling the operation of the electrical device. Conventionally, such selection was obtained by means of a rotary or slide switch having a plurality of positions, where each position corresponds to a set. pointor each combination of a plurality of positions corresponds to a set point. In a switch having number of positions 'N', the number of the set points is 'N' when each position corresponds to each set point. Also, with the onset of miniaturized electrical devices having still increased controllable functions, the use of rotary or slide switches as means to control the operation of the electrical devices, is becoming even less feasible from a space standpoint along with escalating costs.
To overcome the afore-mentioned drawbacks of the conventionally used switches, variable resistance devices, such as potentiometers with inbuilt indentations are being used in electrical circuits to provide a means for selection of parametric functions in the electrical devices. The potentiometers are mechanically adjustable variable resistive devices which are commonly used when an electric signal indicating the amount of displacement of an object is required. The potentiometer comprises: a resistive element, a sliding contact or wiper, electrical terminals at each end of the resistiveelement, a mechanism that moves the wiper from one end of the element to other, and a housing containing the element and the wiper. The physical position of the wiper along the resistive element determines the potentiometers selected resistance. The potentiometer can be a rotary potentiometer which has indentations at equal intervals for indexing the position. A voltage divider is created across the potentiometer; this voltage created across one end and the wiper of the potentiometer can be measured by an analog to

digital converter whose digital value represents the position of the potentiometer. When such a potentiometer is suitably indexed, the specific digital value of the ADC (analog to digital converter) represents the position to which the potentiometer is indexed.
The method using an analog to digital converter within a microcontroller or microprocessor would generally require the use of such device necessarily incorporating the said function. Such a requirement limits choice of possible microcontrollers usable as well as increases the cost of the solution.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to overcome the afore-said drawbacks of the known methods for determining positioning of a potentiometer.
Accordingly, an object of the present invention is to provide a method that accurately determines the position of an indented potentiometer and an apparatus thereof which is simple, minimizes cost and gives wider choice of devices to meet the objective of parameter selection.
These objects and other advantages of the present invention will be more apparent from the following description of the preferred embodiments of the present invention.
In accordance with the present invention, there is provided a method for determining a
potentiometer indexed position, said method comprising:
providing a timing circuit comprising at least one potentiometer and a capacitor in
operative communication with a microcontroller, said potentiometer having a resistance
R, a resistance R1 from a first end of the potentiometer to a wiper, and a resistance R2
from a second end of the potentiometer to the wiper;
determining time (t1 required for said capacitor to charge and time (t1) required for said
capacitor to discharge by alternately putting said resistances R1 and R2 in said timing
circuit, where, t1 is proportional to resistance R1 between said first end of said

potentiometer and said wiper, and t2 is proportional to resistance R2 between said second end of said potentiometer and said wiper; and
determining said potentiometer indexed position using the formula: [t1l(t1+t2)]*total number of said potentiometer positions.
Typically, in accordance with the present invention, said method comprises the step of separating said first end of said potentiometer from said second end of said potentiometer by means of a device selected from a diode, a transistor, an electronic switch and a mechanicalswitch.
Alternatively, said method comprises providing a multiplexer for selecting between more than one potentiometer.
In accordance with the present invention, there is provided an apparatus for determining
a potentiometer indexed position, said apparatus comprising:
at least one potentiometer having a resistance R, a resistance R1 from a first end of the
potentiometer to a wiper, and a resistance R2 from a second end of the potentiometer to
the wiper;
a capacitor; and
a microcontroller adapted to "alternately put said resistances R1 and R2 in a timing
circuit to determine time (t1) required for said capacitor to charge and time (t2) required
for said capacitor to discharge, where, t1 is proportional to resistance R1 between said'
first end of said potentiometer and said wiper, and t2 is proportional to resistance R2
between said second end of said potentiometer and said wiper; and calculate said
potentiometer indexed position using the formula: [t1/(t1+t2)]*total number of said
potentiometer positions.
Typically, in accordance with the present invention, said microcontroller comprises Schmitt input gates adapted to calculate an upper threshold voltage and a lower threshold voltage during charging and discharging of said capacitor through said resistances R1 and R2.

Preferably, in accordance with the present invention, a device selected from a diode, a transistor, an electronic switch and a mechanical switch is provided to isolate said first end of said potentiometer from said second end of said potentiometer.
Alternatively, a multiplexer is provided for selecting between more than one potentiometer.
Typically, in accordance with the present invention, said potentiometer is an indented potentiometer adapted to be driven by means selected from a shaft, a rotor, a knob, and a driver.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present invention will be described here below with reference to the following drawings, in which,
FIG. 1 illustrates a block diagram of the methodology for determining the positioning of a potentiometer in accordance with the present invention;
FIG. 2A illustrates a schematic of a preferred embodiment of the present invention;
FIG. 2B illustrates a schematic of another preferred embodiment of the present invention;
FIG. 2C illustrates a schematic of yet another preferred embodiment of the present invention;
FIG. 3 illustrates a graph showing the charging and discharging time intervals of the capacitor.

DETAILED DESCRIPTION OF THE INVENTION
The invention will now be described in detail with reference to the preferred embodiments illustrated in the accompanying drawings, which are illustrated in use as apparatus for determining positioning of a potentiometer. Reference to the embodiments and the use thereof does not limit the scope of the invention in any way and is to be considered as illustrative with the only purpose of exemplifying the invention.
The present invention envisages a method for determining a potentiometer indexed position. FIGURE 1 of the accompanying drawings is a block diagram illustrating the methodology for determining the positioning of a potentiometer in accordance with the present invention. A microcontroller is provided in operative communication with a timing circuit comprising at least one potentiometer and a capacitor. The microcontroller is adapted to control a switching circuit for alternating putting a resistance R1 from a first end of the potentiometer to a wiper and a resistance R2 from a second end of the potentiometer to the wiper in the timing circuit. Further, the microcontroller calculates the time (ti) required for the capacitor to charge and time (t2) required for the capacitor to discharge, where, t1 is proportional to resistance R1 between the first end of the potentiometer and the wiper, and t2 is proportional to resistance R2 between the second end of the potentiometer and the wiper. The potentiometer indexed position is then calculated by the microcontroller using the formula: [t1/(t1+f2)]*total number of the potentiometer positions, rounded off to the nearest whole number. The method can be implemented as described above or other means to detect the time required for Resistor-Capacitor to charge/discharge such as described below. One such way would be to use a reference resistor along with the circuit capacitor and compare the charge, discharge time with that of the potentiometer along with the same circuit capacitor, the potentiometer being used in two terminal mode with wiper connected to one of its ends. The implementation of time comparisons in above methods could also be accomplished by measuring the frequency of oscillation using the said potentiometers and reference capacitor or resistor, instead of using a charge and discharge timings.

FIGURES 2A, 2B & 2C of the accompanying drawings illustrate the preferred embodiments of the apparatus for determining a potentiometer indexed position of the present invention. The apparatus comprises at least one potentiometer having a resistance (R), a resistance (R1)from a first end of the potentiometer to a wiper, and a resistance (R2) from a second end of the potentiometer to the wiper; a capacitor (C); and a microcontroller (M) adapted to alternately put the resistances R1 and R2 in a timing circuit. The microcontroller (M) is adapted to determine time (t1) required for the capacitor (C) to charge and time (t2) required for the capacitor (C) to discharge, where, t1 is proportional to resistance (R1) between the first end of the potentiometer and the wiper, and t2 is proportional to resistance (R2) between the second end of the potentiometer and the wiper; and calculate the potentiometer indexed position using the formula: [t1/(t1+T2)]*total number of the potentiometer positions. The microcontroller (M) comprises Schmitt input gates adapted to calculate an upper threshold voltage and a lower threshold voltage during charging and discharging of said capacitor through said resistances R1 and R2.
FIG. 2A of the accompanying drawings illustrates a preferred embodiment of the apparatus comprising a diode (D1) & (D2) adapted to isolate the first end of the potentiometer from the second end of the potentiometer. FIG. 2B of the accompanying drawings illustrates a preferred embodiment of the apparatus-comprising a transistor (Q1) & (Q2) adapted to isolate the first end of the potentiometer from the second end of the potentiometer. FIG. 2C of the accompanying drawings illustrates, a preferred, embodiment of the apparatus comprising an electric switch (SW1) & (SW2) adapted to isolate the first end of the potentiometer from the second end of the potentiometer.
The indexation means for the potentiometer, could be obtained either by using a readily available commercial indented/indexed potentiometer operated by a driving external shaft/knob/rotor/driver or an external indexation means in co-operation with a standard potentiometer. The external indexation means may have several notches on shaft/knob/rotor/driver and snap locking lever which is part of apparatus assembly

getting engaged with at least one of the notches used in co-operation with the standard potentiometer without inbuilt indexation.
An electric device may have several parameters, each having the need to select from one of many parametric selections, therefore needing a plurality of indexed/indented potentiometers. The electric device having multiple potentiometers is thus provided with a multiplexer for alternate potentiometer selections for detection of one's position.
FIG. 3 of the accompanying drawings illustrates a graph showing the charging and discharging time intervals of the capacitor (C).
There are two ports required in the Microcontroller M, Port P1 & Port P2. The input port line P2 is of Schmitt input type which has an upper threshold function for a rising input and lower threshold for a falling input.
The principle is to check the ratio of the resistance between the two arms of the potentiometer from the wiper. This will give the potentiometer position.
Port P2 is a Schmitt input. Port P1 is toggled between high and low states.
When port P1 is first low & then made high; the input at P2 will reach its upper Schmitt threshold. Immediately, P1 will be made low. In time t1 it will reach the lower threshold. Once more it will be made high. In time t2, it will reach the upper threshold. The ratio of t1 to (t1+t2) will represent the position of the potentiometer.
Typically, the time cycle is kept between 5 ms to 10 ms. The potentiometer resistance & capacitor are chosen accordingly.
The formula for current indexed position is: [t1/(t1 + t2)]*total number of the potentiometer positions.
where,

t1 is the time required for the capacitor to charge, from Port P2 lower threshold to upper
threshold, directly proportional to one end of the potentiometer (A) & the wiper (R1);
t2 is the time required for the capacitor to discharge, from Port P2 upper threshold to
lower threshold, directly proportional to other end of the potentiometer (B) & the wiper
(R2);
Total number of the potentiometer positions is the No. of Potentiometer steps desired.
Embodiment of the present invention is applicable over a wide number of uses and other embodiments may be developed beyond the embodiment discussed heretofore. Only the most preferred embodiments and their uses have been described herein for purpose of example, illustrating the advantages over the prior art obtained through the present invention; the invention is not limited to these specific embodiments or their specified uses. Thus, the forms of the invention described herein are to be taken as illustrative only and other embodiments may be selected without departing from the scope of the present invention. It should also be understood that additional changes and modifications, within the scope of the invention, will be apparent to one skilled in the art and that various modifications to the construction described herein may fall within the scope of the invention.

WE CLAIM
1. A method for determining a potentiometer indexed position, said method
comprising:
providing a timing circuit comprising at least one potentiometer and a capacitor in
operative communication with a microcontroller, said potentiometer having a resistance
R, a resistance R1 from a first end of the potentiometer to a wiper, and a resistance R2
from a second end of the potentiometer to the wiper;
determining time (t1) required for said capacitor to charge and time (f2) required for said
capacitor to discharge by alternately putting said resistances R1 and R2 in said timing
circuit, where, t1 is proportional to resistance R1 between said first end of said
potentiometer and said wiper, and t2 is proportional to resistance R2 between said
second end of said potentiometer and said wiper; and
determining said potentiometer indexed position using the formula: [t1/(t1+t2)]*total
number of said potentiometer positions.
2. The method as claimed in claim 1, wherein said method comprises the step of separating said first end of said potentiometer from said second end of said potentiometer by means of a device selected from a diode, a transistor, an electronic switch and a mechanical switch.
3. The method as claimed in claim 1, wherein said method comprises providing a multiplexer for selecting between more than one potentiometer.
4. An apparatus for determining a potentiometer indexed position, said apparatus comprising:
at least one potentiometer having a resistance R, a resistance R1 from a first end of the potentiometer to a wiper, and a resistance R2 from a second end of the potentiometer to the wiper; a capacitor; and

a microcontroller adapted to alternately put said resistances R1 and R2 in a timing circuit to determine time (t1) required for said capacitor to charge and time (t2) required for said capacitor to discharge, where, t1 is proportional to resistance R1 between said first end of said potentiometer and said wiper, and t2 is proportional to resistance R2 between said second end of said potentiometer and said wiper- and calculate said potentiometer indexed position using the formula: [t1/(t1+t2)]*total number of said potentiometer positions.
5. The apparatus as claimed in claim 4, wherein said microcontroller comprises Schmitt input gates adapted to calculate an upper threshold voltage and a lower threshold voltage during charging and discharging of said capacitor through said resistances R1 and R2.
6. The apparatus as claimed in claim 4, wherein a device selected from a diode, a transistor, an electronic switch and a mechanical switch is provided to isolate said first
end of said potentiometer from said second end of said potentiometer.
*
7. The apparatus as claimed in claim 4, wherein a multiplexer is provided for selecting between more than one potentiometer.
8. The apparatus as claimed in claim 4, wherein said potentiometer is an indented potentiometer adapted to be driven by means selected from a shaft, a rotor, a knob, and a driver.