Circuits and methods for capacitively sensing states of loads

Abstract

A circuit for equipment may include a microcontroller, a printed circuit board (PCB) having a first side and a second side, and a capacitive sensor. The capacitive sensor may include a first pad and a second pad, where the first pad is located on the first side of the PCB and the second pad is located on the second side of the PCB. The first pad may be operatively coupled to a relay contact and a load, and the second pad may be operatively coupled to the microcontroller. The microcontroller may be configured to sense a state of the load based on a capacitance value of the capacitive sensor, adjust at least one system parameter of the home appliance based on the capacitance value, and / or control the relay contact between an open state and a closed state.

Description

CIRCUITS AND METHODS FOR CAPACITIVELY SENSING STATES OF LOADSFIELD OF THE INVENTION

[0001] The present invention relates to a galvanically isolated means of sensing the output state of a relay in a circuit.BACKGROUND

[0002] In electronic equipment and other applications, ensuring that an appliance or piece of equipment is operating in a safe manner typically requires knowing the output state of a relay. For example, in a home appliance such as a hob or cooktop, it is beneficial to know if a relay that controls a heating element is open (i.e., turned off) when commanded to turn off.BRIEF SUMMARY

[0003] The following presents a simplified summary of one or more embodiments of the invention in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments, nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0004] In one aspect, the present invention is directed to equipment including a capacitive sensor that includes a first pad and a second pad, where the first pad is galvanically isolated from the second pad. The equipment may include a load circuit that includes a load, a switch for controlling a state of the load, and the first pad, where the first pad is positioned between the load and the switch. The equipment may include a micro-control unit (MCU) electrically connected to the second pad.

[0005] In some embodiments, the MCU may be configured to determine whether the load is on or off based on a voltage at the capacitive sensor.

[0006] In some embodiments, the MCU may be configured to control the switch to turn the load on and off.

[0007] In some embodiments, the MCU may be configured to control the switch between an open state and a closed state.

[0008] In some embodiments, the MCU may be configured to determine, based on a sensed voltage at the capacitive sensor, a load voltage at the load and adjust, based on the load voltage at the load, at least one system parameter of the equipment.

[0009] In some embodiments, the MCU may be configured to determine, based on a sensed voltage at the capacitive sensor, a zero-crossing associated with a load voltage at the load and adjust, based on the zero-crossing, a clock of the equipment.

[0010] In some embodiments, the load may be a heating element of the equipment.

[0011] In some embodiments, the equipment may include a printed circuit board (PCB) having a first side and a second side, where the PCB includes a dielectric material, and where the first pad of the capacitive sensor is located on the first side of the PCB and the second pad of the capacitive sensor is located on the second side of the PCB.

[0012] In some embodiments, the load circuit may include a diode positioned between a resistor and the MCU, a diode positioned in series with the resistor, a pull-up resistor connected between the MCU and a voltage supply of the MCU, and / or the like.

[0013] In some embodiments, the equipment may include a plurality of switches, where each switch is operatively coupled to one of a plurality of capacitive sensors.

[0014] In some embodiments, the equipment may include a second capacitive sensor connected to a power rail, where the second capacitive sensor is configured to sense a reference value of the power rail.

[0015] In another aspect, the present invention may be directed to a method of controlling an apparatus. The method may include determining a voltage at a capacitive sensor, where the capacitive sensor includes a first pad and a second pad galvanically isolated from the first pad, where the first pad is between a load and a switch in a load circuit, and where the switch is configured to control a commanded state of the load. The method may include determining, based on the voltage, an actual state of the load and determining whether the actual state of the load corresponds to an expected state of the load.

[0016] In some embodiments, the expected state of the load may be the commanded state of the load.

[0017] In some embodiments, the method may include instructing, in response to determining that the actual state of the load does not correspond to the expected state of the load, a secondary switch to turn off the load.

[0018] In some embodiments, the method may include determining, based on the voltage at the capacitive sensor, a voltage at the load and adjusting, based on the voltage at the load, at least one system parameter of the apparatus.

[0019] The features, functions, and advantages that have been discussed may be achieved independently in various embodiments of the present invention or may be combinedwith yet other embodiments, further details of which can be seen with reference to the following description and drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Having thus described embodiments of the invention in general terms, reference will now be made to the accompanying drawings.

[0021] Figures 1A-1B illustrate circuits for equipment, in accordance with embodiments of the invention.

[0022] Figures 2A-2C illustrate portions of circuits for equipment, in accordance with embodiments of the invention.

[0023] Figure 3 illustrates a circuit including a printed circuit board, in accordance with an embodiment of the invention.

[0024] Figure 4 illustrates a circuit including multiple capacitive sensors, in accordance with an embodiment of the invention.

[0025] Figure 5 illustrates a circuit including multiple capacitive sensors, in accordance with an embodiment of the invention.

[0026] Figure 6 illustrates an exemplary graph of a voltage sensed by a reference sensor and a voltage sensed by a relay capacitive sensor, in accordance with an embodiment of the invention.

[0027] Figures 7 and 8 illustrate exemplary graphs of a voltage sensed by a reference sensor and a voltage sensed by a relay capacitive sensor, in accordance with an embodiment of the invention.

[0028] Figure 9 illustrates exemplary graphs of input and output voltages, in accordance with an embodiment of the invention.DETAILED DESCRIPTION OF THE INVENTION

[0029] Embodiments of the present invention now may be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure may satisfy applicable legal requirements. Like numbers refer to like elements throughout.

[0030] In electric equipment and other applications, ensuring that an appliance or piece of equipment is operating in a safe manner typically involves knowing the output state of arelay. For example, in a home appliance, such as a hob or cooktop, it is beneficial to know if a relay that controls a heating element is open (i.e., turned off) when commanded to turn off. In a vehicle, it is beneficial to know if a relay that controls a battery-powered element such as a light bulb is turned off, to avoid unintended battery usage. Furthermore, in industrial equipment, it is beneficial to know whether a relay that controls a piece of machinery is turned off when commanded, in order to increase operator safety. Solutions to sense the state of a relay may involve sensing a load voltage using optocouplers, high voltage resistor dividers, current transformers, voltage transformers or similar components. Each of these components adds additional cost and complexity.

[0031] In some embodiments, the present invention may be directed to a low cost, galvanically isolated means of detecting the state of relay contacts or other switches by using capacitive sensing and, therefore, may be more efficient than other galvanically isolated solutions, such as using optocouplers and / or current or voltage transformers. In some embodiments, the present invention may be more efficient than solutions that are not galvanically isolated, such as using a high-voltage resistor divider connected to a microcontroller’s analog-to-digital converter port. Such embodiments may also be more efficient than (i) a non-isolated current sensing scheme detecting the load current for loads referenced to neutral and (ii) a current sensing scheme when loads are not referenced to neutral.

[0032] In some embodiments, the present invention may be directed to using galvanically isolated capacitive sensing to sense the state of relay contacts used to control high voltage loads and detect when the relay output state is different from an intended or commanded state. In some embodiments, the present invention may be directed to detecting when electric equipment (e.g., an appliance) is powered at 208 volts of alternating current (VAC) versus 240 VAC and adjusting system parameters and / or algorithms of the electric equipment accordingly. Some embodiments of the present invention may also detect the analog voltage level and / or the frequency of an applied voltage and adjust system parameters and / or algorithms accordingly. Finally, some embodiments of the present invention may be used to detect a zero crossing of an alternating current (AC) voltage in order to, for example, maintain accurate time for one or more clocks, control when one or more relays are turned on or off, and / or control when one or more triodes for alternating current (TRIACs) are turned on.

[0033] Also, it will be understood that, where possible, any of the advantages, features, functions, devices, and / or operational aspects of any of the embodiments of the present invention described and / or contemplated herein may be included in any of the otherembodiments of the present invention described and / or contemplated herein, and / or vice versa. In addition, where possible, any terms expressed in the singular form herein are meant to also include the plural form and / or vice versa, unless explicitly stated otherwise. Accordingly, the terms “a” and / or “an” shall mean “one or more.”

[0034] Figure 1A illustrates an exemplary embodiment of the invention. In some embodiments, the present invention may include a circuit 100 that includes a microcontroller or micro-control unit (MCU) 110, a load 120, a switch 131, a capacitive sensor 140, a resistor 150, and a neutral or ground point 101. The switch 131 may be a relay that includes a relay contact 130. In other specific embodiments, the switch 131 may be a contactor or other type of switch. As illustrated, the load 120 may be connected with the neutral or ground point 101. The load 120 may include a heating element and / or other equipment components having an on / off state. In some embodiments, the load may be controlled by the switch 131 such that when the switch 131 is closed, the load 120 is turned on, and when the switch 131 is open, the load 120 is turned off. If the switch 131 is a relay, the relay contact 130 is closed to turn the load 120 on, and the relay contact 130 is opened to turn, the load 120 off. The switch 131 may be controlled by the MCU 110. If the switch 131 is a relay, the switch 131 may also include a relay coil. The relay coil may be controlled by the MCU 110 and may be configured to control the relay contact 130.

[0035] As shown in Figure 1A, the capacitive sensor 140 may include a first pad 140a and a second pad 140b. As also shown in Figure 1A, the first pad 140a may be in electrical connection between the switch 131 and the load 120. In this regard, in some embodiments, current flowing from the switch 131 may flow through the first pad 140a to the load 120. In some embodiments, the state of the load 120 and the switch 131 may be fed to a port on the MCU 110 via the capacitive sensor 140 (e.g., in particular the second pad 140b) and the resistor 150. In the illustrated example, the voltage between the neutral or ground point 101 and a first line or power rail 102 is 120 VAC, although the load 120 may additionally or alternatively be powered at other voltages. Thus, when the switch 131 is open, the voltage at the capacitive sensor 140 (i.e., the voltage between the relay contact 130 and load 120) will be zero. When the switch 131 is closed, the voltage at the capacitive sensor 140 will be 120 VAC.

[0036] Figure IB illustrates an equivalent circuit 160 to the circuit 100. The equivalent circuit 160 may include the capacitive sensor 140 having a capacitance value Cl, the resistor 150 having a resistance value Rl, an MCU input port 111 of the MCU 110, and a voltage source 161 (e.g., for the load 120 and / or the MCU 110). The MCU input port 111 may have aresistance value 112 and a capacitance value 113, where the resistance value 112 and the capacitance value 113 are representative of an input impedance of the MCU input port 111. In some embodiments, the value of R1 may be selected to protect the MCU 110 from transient events (e.g., electrostatic discharge events) and from negative voltages at the MCU input port 111 created by the AC input voltage of voltage source 161. The value of Cl may be selected to provide sufficient signal to the MCU 110 for sensing.

[0037] Figures 2A-2C illustrate exemplary embodiments of portions of the circuit 100 of Figures 1A-1B. For example, Figures 2A-2C illustrate the portion of the circuit 100 including the MCU 110, the resistor 150, and the second pad 140b of the capacitive sensor 140. However, Figures 2 A and 2B illustrate the portion of the circuit 100 with the addition of a diode designed to protect the MCU 110 from negative voltage. Figure 2A illustrates the portion of the circuit 100 with a Schottky diode 210 positioned between the resistor 150 and the MCU 110. The Schottky diode 210 may have a capacitance value equivalent to the capacitance value 113 of the MCU 110 as illustrated in Figure IB. Figure 2B illustrates the portion of the circuit 100 with a diode 220 (e.g., a Schottky diode, a general purpose diode, and / or the like) positioned in series with the resistor 150, such that the forward voltage of the diode 220 reduces the voltage at the MCU 110 and prevents negative voltage at the MCU 110. Furthermore, in some embodiments, it may be desired to have an entire voltage waveform presented at the MCU input port 111. This may be accomplished by adding a pull-up resistor 230 as illustrated in Figure 2C, where the pull-up resistor 230 is connected between the MCU 110 and a voltage supply of the MCU 110 (not illustrated).

[0038] Figure 3 illustrates an exemplary embodiment of the circuit 100 as described in greater detail with respect to Figure 1. As illustrated in Figure 3, the capacitive sensor 140 may be formed from the first pad 140a and the second pad 140b, where the first pad 140a and the second pad 140b are located on opposite sides of a printed circuit board (PCB) 300. For example, the first pad 140a may be located on a top surface of the PCB 300 and may be connected between the relay contact 130 and the load 120. The second pad 140b may be located on a bottom side of the PCB 300 and may be connected to the MCU 110 through the resistor 150. In some embodiments, the area (A) of each pad can be calculated by: A= (C*d) / a where, C = the desired capacitance for sensing, d = a thickness of the PCB 300, and a = permittivity of the dielectric material of the PCB 300.

[0039] In some embodiments, the capacitive sensor 140 may not be created by rectangular pads. In some embodiments, the pads may be any shape which may be dictated bythe available space on the PCB 300, including parallel traces, while achieving the desired capacitance. While the capacitive sensor 140 does not need to be created by pads on opposite sides of the PCB 300, there are advantages in doing so. For example, the PCB material, such as FR4 material and / or the like, may provide electrical isolation between the load 120 and MCU 110. If the pads 140a and 140b are on the same side of the PCB 300 (e.g., parallel traces), the separation of the traces may be greater (e.g., to reduce the capacitance), and the length of the parallel traces may need to be longer to achieve the desired capacitance.

[0040] Figure 4 illustrates an exemplary embodiment of a circuit 400. In some embodiments, the circuit 400 may include the MCU 110, the load 120, the switch 131 (which may be a relay including the relay contact 130), the capacitive sensor 140, the resistor 150, the neutral or ground point 101, and the power rail 102 as described in greater detail with respect to Figure 1. As shown in Figure 4, the circuit 400 may include an additional capacitive sensor 141 and an additional resistor 151, thereby enabling a mutual capacitance mode of sensing. For example, the MCU 110 may include a capacitive touch peripheral. The capacitive sensor 141 may be located at the power rail 102 and include a first pad 141a between the power rail 102 and the switch 131 and a second pad 141b connected to the MCU 110 via the additional resistor 151. In some embodiments, the MCU 110 may include a transmit port (Tx) and a receive port (Rx), where the resistor 151 is connected to the transmit port and the resistor 150 is connected to the receive port of the mutual capacitance touch peripheral. The MCU 110 may place a signal at Tx, which may couple through a capacitance between Tx and Rx such that a portion of the signal may be detected at Rx. Thus, when the switch 131 is open, the capacitances of capacitive sensors 140 and 141, as well as the capacitance of the switch 131, may be in series between Tx and Rx. When the switch 131 is closed, the capacitances of capacitive sensors 140 and 141, but not the capacitance of the switch 131, are in series between Tx and Rx. Therefore, when the switch 131 is closed, the signal at Rx may exceed the signal at Rx when the switch 131 is opened. In this way, the MCU 110 may determine whether or not current is being supplied to the load 120.

[0041] In the illustrated example of Figure 4, the voltage between the neutral or ground point 101 and the first line or power rail 102 is 120 VAC. However, in some embodiments, loads may be powered at other voltages, such as 208 VAC or 240 VAC. In this regard, Figure 5 illustrates an exemplary embodiment of a circuit 500, which may include a load powered at 208 VAC or 240 VAC. In some embodiments, the circuit 500 may include the MCU 110, the load 120, the switch 131 (which may be a relay including the relay contact 130), the capacitivesensor 140, the additional capacitive sensor 141, the resistor 150, the additional resistor 151, the neutral or ground point 101, and the power rail 102 as described in greater detail with respect to Figure 4. However, as shown in Figure 5, the circuit 500 includes an additional power rail 103 for the load 120, and the neutral or ground point 101 is not one of the power rails of the load 120. Thus, when the switch 131 is open, the voltage at the net between the switch 131 and the load 120 will not be zero, as described with respect to Figure 1, but will be the AC voltage at power rail 103 with respect to the neutral or ground point 101. In such embodiments, the capacitive sensor 141, connected to the first line or power rail 102, may operate as a reference capacitive sensor and may sense the voltage at the first line or power rail 102. The capacitive sensor 140, connected between the switch 131 and the load 120, may operate as a relay capacitive sensor.

[0042] Figure 6 illustrates an exemplary graph 600 of the voltage 610 sensed by the reference sensor (i.e., the capacitive sensor 141) and the voltage 620 sensed by the relay capacitive sensor (i.e., the capacitive sensor 140) when the switch 131 is open and the load 120 is powered at 240 VAC for the circuit 500 of Figure 5. As shown in Figure 6, when the switch 131 is open and the load 120 is powered, the relay capacitive sensor (i.e., the capacitive sensor 140) may sense the voltage 620 at the second line or power rail 103, and the voltages 610 and 620 (i.e., at 102 and 103) will be 180 degrees out of phase. When the switch 131 is closed and the load 120 is not powered, the relay capacitive sensor (i.e., the capacitive sensor 140) may detect only the voltage at the first line or power rail 102, which is the same voltage detected by the reference sensor (i.e., the capacitive sensor 141), and the voltages detected by the relay capacitive sensor (i.e., the capacitive sensor 140) and the reference sensor (i.e., the capacitive sensor 141) will be in phase.

[0043] Figures 7 and 8 illustrate exemplary graphs 700 and 800 of the voltage 710 sensed by the reference sensor (i.e., the capacitive sensor 141) and the voltage 720 sensed by the relay capacitive sensor (i.e., the capacitive sensor 140) when the switch 131 is open and the load 120 is powered at 208 VAC for the circuit 500 of Figure 5. When the switch 131 is open and the load 120 is powered at 208 VAC, the voltage 710 sensed by the reference sensor (i.e., the capacitive sensor 141) will be 120 degrees out of phase with the voltage 720 sensed by the relay capacitive sensor (i.e., the capacitive sensor 140) as shown in Figure 7 or -120 degrees out of phase as shown in Figure 8. When the switch 131 is closed, the voltage 710 and the voltage 720 will be in phase. In some embodiments, the circuit 500 may be powered by either a 208 VAC voltage source or a 240 VAC voltage source, and the MCU 110 may be configuredto detect the voltage powering the circuit 500 and adjust one or more system parameters accordingly. For example, in some embodiments, the MCU 110 may adjust a transformer of the equipment to achieve a more constant output voltage and increase equipment efficiency. As another example, the MCU 110 may adjust the controls of a heating element to maintain a level of power regardless of the level of voltage. As another example, in some embodiments, the MCU 110 may detect an abnormal level of voltage based on an expected level of voltage, and may shut down the equipment and / or warn an operator of the equipment of the abnormal level of voltage.

[0044] Figure 9 illustrates exemplary graphs 900 and 950 of input and output voltages when the switch 131 is open and the load 120 is powered at 240 VAC for the circuit 500 of Figure 5. The voltage Vref in graph 900 corresponds to the voltage at the MCU port of the reference sensor (i.e., the capacitive sensor 141), which also corresponds to the voltage V(L1) in graph 950. The voltage Vrl in graph 900 corresponds to the voltage at the MCU port of the relay capacitive sensor (i.e., the capacitive sensor 140), which also corresponds to V(L2) in the graph 900. The ports of the MCU 110 of the circuit 500 may have impedances modeled by capacitances and resistances in an equivalent circuit for circuit 500 in a manner similar to that described herein with respect to Figures 1A-1B. Such capacitances may cause a phase shift between V(L1) and Vref and a phase shift between V(L2) and V(rl), as shown in Figure 9. However, the capacitances may be known capacitances, thereby allowing a calculation of these phase shifts. In some embodiments, the capacitances may be the same, such that the phase relationship between Vref and V(rl) may be the same as the phase relationship between V(L1) and V(L2), as shown in Figure 9. Using the known relationships between Vref, Vrl, V(L1), and V(L2), the MCU 110 may be configured to determine whether the switch 131 is open or closed.

[0045] In some embodiments, equipment may include a plurality of switches (e.g., similar to the switch 131). In such embodiments, if the switches are connected to 120 VAC and the neutral is the same potential as the ground of the MCU, the circuits of the equipment may include one capacitive sensor for each switch to determine whether each switch is open or closed. In such embodiments, if the switches are connected to 208 VAC or 240 VAC, the circuits of the equipment may include one capacitive sensor for each switch and at least one additional capacitive sensor (e.g., as a reference sensor) to determine whether each switch is open or closed.

[0046] Although the embodiments described herein refer to voltages of 120 VAC, 208 VAC, and 240VAC, those skilled in the art will appreciate that the sensing methods may be applied to circuits powered by other voltages in view of the present disclosure. For example, circuits of industrial controls powered at 480 V three-phase (277 phase-to-neutral) may also employ embodiments of the presently described sensing methods to determine whether one or more switches are open or closed. In some embodiments, the presently described sensing methods may be applied to different frequencies (e.g., 50 Hz, 60 Hz, and / or the like).

[0047] In some embodiments, the presently described sensing methods may be used to determine the state of a contactor. For example, each of the three contacts of a three-phase contactor may be sensed independently, and an MCU may detect if any of the contacts fail to operate properly. Furthermore, embodiments of the presently described sensing method may be applied to solid state devices, such as TRIACs, silicon-controlled rectifiers (SCRs), solid- state relays, and / or the like, and may be used to determine whether a component has failed, shorted, or is open.

[0048] As will be appreciated by those of ordinary skill in the art in view of the present disclosure, the circuits and / or the sensing methods described herein may be employed by various devices, equipment, and / or systems. For example, an appliance (e.g., an oven, range, cooktop, toaster, and / or the like) may include a load, such as a heating element, a motor, a fan, and / or the like, and the appliance may include one or more circuits employing one or more of the sensing methods described herein to determine whether a switch (e.g., an electromechanical relay, an electromechanical contactor, a solid state relay, a TRIAC, and / or the like) for controlling a state (e.g., on or off) of the load is in an expected state (e.g., open or closed), determine a voltage applied to the load, and / or determine a frequency of the voltage applied to the load. In such an example, the appliance may adjust one or more operating parameters of the appliance based on whether the switch is in the expected state, the determined voltage, and / or the determined frequency. For example, the appliance may close or open a secondary switch, adjust control of a heating element, and / or control a clock or timer. Other devices, equipment, and / or systems may include industrial equipment (e.g., contactors, starters, soft starters, and / or adjustable frequency drives, which may be used to control industrial loads such as fans, conveyors, presses, mills, welders, winders, saws and / or the like).

[0049] While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative of and not restrictive on the broad invention, and that this invention not be limited to the specificconstructions and arrangements shown and described, since various other changes, combinations, omissions, modifications and substitutions, in addition to those set forth in the above paragraphs, are possible. Those skilled in the art will appreciate that various adaptations, modifications, and combinations of the just described embodiments can be configured without departing from the scope and spirit of the invention. Therefore, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described herein.

Claims

WHAT IS CLAIMED IS:

1. Equipment comprising: a capacitive sensor comprising a first pad and a second pad, wherein the first pad is galvanically isolated from the second pad; a load circuit comprising a load, a switch for controlling a state of the load, and the first pad, wherein the first pad is positioned between the load and the switch; and a micro-control unit (MCU) electrically connected to the second pad.

2. The equipment of claim 1, wherein the MCU is configured to determine whether the load is on or off based on a voltage at the capacitive sensor.

3. The equipment of claim 1 or claim 2, wherein the MCU is configured to control the switch to turn the load on and off.

4. The equipment of any one of claims 1-3, wherein the MCU is configured to control the switch between an open state and a closed state.

5. The equipment of any one of claims 1-4, wherein the MCU is configured to: determine, based on a sensed voltage at the capacitive sensor, a load voltage at the load; and adjust, based on the load voltage at the load, at least one system parameter of the equipment.

6. The equipment of any one of claims 1-5, wherein the MCU is configured to: determine, based on a sensed voltage at the capacitive sensor, a zero-crossing associated with a load voltage at the load; and adjust, based on the zero-crossing, a clock of the equipment.

7. The equipment of any one of claims 1-6, wherein the load is a heating element of the equipment.

8. The equipment of any one of claims 1-7, further comprising a printed circuit board (PCB) having a first side and a second side, wherein the PCB comprises a dielectric material,and wherein the first pad of the capacitive sensor is located on the first side of the PCB and the second pad of the capacitive sensor is located on the second side of the PCB.

9. The equipment of any one of claims 1-8, wherein the load circuit comprises at least one of a diode positioned between a resistor and the MCU; a diode positioned in series with the resistor; and a pull-up resistor connected between the MCU and a voltage supply of the MCU.

10. The equipment of any one of claims 1-9, further comprising a plurality of switches, wherein each switch is operatively coupled to one of a plurality of capacitive sensors.

11. The equipment of any one of claims 1-10, further comprising a second capacitive sensor connected to a power rail, wherein the second capacitive sensor is configured to sense a reference value of the power rail.

12. A method of controlling an apparatus, the method comprising: determining a voltage at a capacitive sensor, wherein the capacitive sensor comprises a first pad and a second pad galvanically isolated from the first pad, wherein the first pad is between a load and a switch in a load circuit, and wherein the switch is configured to control a commanded state of the load; determining, based on the voltage, an actual state of the load; and determining whether the actual state of the load corresponds to an expected state of the load.

13. The method of claim 12, wherein the expected state of the load is the commanded state of the load.

14. The method of claim 12 or claim 13, further comprising instructing, in response to determining that the actual state of the load does not correspond to the expected state of the load, a secondary switch to turn off the load.

15. The method of any one of claims 12-14, further comprising: determining, based on the voltage at the capacitive sensor, a voltage at the load; and adjusting, based on the voltage at the load, at least one system parameter of the apparatus.

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