Patent Publication Number: US-11658443-B2

Title: Liquid detection and corrosion mitigation

Description:
BACKGROUND 
     The amount of data transferred between electronic devices has grown tremendously the last several years. Large amounts of audio, streaming video, text, and other types of data content are now regularly transferred among desktop and portable computers, media devices, smart phones, displays, storage devices, and other types of electronic devices. 
     Power and data can be provided from one electronic device to another over cables that can include one or more wire conductors, fiber optic cables, or other conductors. Connector inserts can be located at each end of these cables and can be inserted into connector receptacles in the communicating or power transferring electronic devices. Contacts in or on a connector insert can form electrical connections with corresponding contacts in a connector receptacle. Other devices can have contacts at a surface of a device. Pathways for power and data can be formed when devices are attached together or positioned next to each other and corresponding contacts are electrically connected to each other. 
     The various contacts in connector inserts, in connector receptacles, or on a surface of a device, can be exposed to the local environment where they can encounter liquid, moisture, or other damaging contaminants. For example, liquids can be spilled on these contacts or a device can be set down such that its contacts land in a puddle of liquid. Users can swim or exercise while wearing or holding an electric device. These activities can put contacts for the electronic devices in a position to encounter various contaminants such as chlorinated water, sweat, or other moisture. 
     These liquids, moisture, or other contaminants can corrode and damage the contacts. This corrosion can be greatly exacerbated by the presence of an electric potential, such as when a voltage is applied to a contact. Accordingly, it can be desirable for a device to be able to detect the presence of moisture or other contaminant at a contact so that the possible damage can be mitigated. 
     Thus, what is needed are methods, structures, and apparatus that can detect the presence of liquids, moisture, or other contamination at a contact of a connector. 
     SUMMARY 
     Accordingly, embodiments of the present invention can provide methods, structures, and apparatus that can detect the presence of liquid, moisture, or other contamination at a contact of a connector. An illustrative embodiment of the present invention can provide a connector having contacts to mate with corresponding contacts in a corresponding connector. The connector can include an additional contact that does not have a corresponding contact in the corresponding connector. The additional contact can be used to detect the presence of moisture in the connector and can be referred to as a liquid-detect contact. More than one additional contact can be included, for example, a liquid-detect contact can be located on each of a top and bottom side of a connector feature, such as a tongue. The connector can be a connector receptacle while the corresponding connector can be a connector insert. Alternatively, the connector can be a connector insert while the corresponding connector can be a connector receptacle. 
     In these and other embodiments of the present invention, the presence of liquid, moisture, or other contamination (referred to here as liquid for simplicity) can be detected by generating a stimulus voltage signal and applying the stimulus voltage signal (or a voltage signal that tracks the stimulus voltage signal) though an impedance to the liquid-detect contact. A voltage signal at the liquid-detect contact can be determined and referred to as the applied voltage signal. Alternatively, instead of determining the applied voltage signal directly, a voltage proportional to the applied voltage signal at the liquid-detect contact, an inverse of the applied voltage signal at the liquid-detect contact, or a voltage proportional to the inverse of the applied voltage signal at the liquid-detect contact can be determined and referred to as the measured voltage signal. In this way, the measured voltage signal can directly track and be used as a proxy for the actual applied voltage signal at the liquid-detect contact. A current through the impedance can be determined and referred to as the resulting current. 
     In these and other embodiments of the present invention, the stimulus voltage signal can be a sinewave, for example a low-frequency sinewave. The stimulus voltage signal can be generated using pulse-density modulation (PDM) and filtering to achieve a desired spectral purity. The stimulus voltage can alternatively be generated using a digital-to-analog converter (DAC) along with filtering to achieve the desired spectral purity. The stimulus voltage signal can be provided to a transimpedance amplifier. The transimpedance amplifier can generate a voltage signal that tracks or follows the stimulus voltage signal and can apply that tracking voltage signal through an impedance to the liquid-detect contact. A resulting current can flow through an input resistor and a feedback resistor of the transimpedance amplifier, thus generating a measured voltage signal. The measured voltage signal can be the inverse of the voltage at the liquid-detect contact or a voltage proportional to the inverse of the voltage at the liquid-detect contact. The stimulus voltage signal and the measured voltage signal can be digitized using an analog-to-digital converter (ADC.) The stimulus voltage signal and the measured voltage signal can be used to determine the presence of liquid at the liquid-detect contact. For example, an impedance at the liquid-detect contact can be found using the amplitudes and relative phases of the stimulus voltage signal and the measured voltage signal. The magnitude and phase of the determined impedance can then be used to determine the presence of liquid at the liquid-detect contact. 
     In these and other embodiments of the present invention, the stimulus voltage signal can be a series of pulses. As before, a stimulus voltage signal can be provided to a transimpedance amplifier. The transimpedance amplifier can generate a voltage signal that tracks or follows the stimulus voltage signal and can apply that tracking voltage signal through an impedance to the liquid-detect contact. A resulting current can flow through an input resistor and a feedback resistor of the transimpedance amplifier, thus generating a measured voltage signal. The measured voltage signal can be the inverse of the voltage at the liquid-detect contact or a voltage proportional to the inverse of the voltage at the liquid-detect contact. The stimulus voltage signal and the measured voltage signal can be digitized using an analog-to-digital converter (ADC.) An impedance at the liquid-detect contact can be found by determining the high-frequency roll-off of the measured voltage signal, as well as the initial overshoot, the settled amplitude, and the undershoot of the measured voltage signal. 
     In these and other embodiments of the present invention, the liquid-detect contact can be implemented in various ways. For example, the liquid-detect contact can be implemented on a tongue in a connector receptacle, such as a Universal Serial Bus Type-C connector receptacle. The tongue can be formed of a printed circuit board, where contacts (or contacting portions of contacts), including the liquid-detect contact, can be formed as pads on surfaces of the printed circuit boards. The printed circuit board can be supported by a metal frame. The liquid-detect contact can be positioned where it might make only incidental contact with ground contacts or other contacts during mating with a corresponding connector insert. The liquid-detect contact can be positioned where it does not connect to any contact in the corresponding connector insert when mated. For example, the liquid-detect contact can be positioned between signal (and power) contacts and a ground pad on the tongue. Liquids that form a current path between the liquid-detect contact and another contact, such as a power supply contact or connection-detect contact, can be detected. 
     In these and other embodiments of the present invention, the tongue can be formed of plastic molding. The plastic molding can be supported by a metallic frame. The tongue can further include a liquid-detect contact formed as center plate between contacts on a top side of the tongue and contacts on the bottom surface of the tongue. The molding can include passages from a top surface of the tongue to the liquid-detect contact, as well as passages from the bottom surface of the tongue to the liquid-detect contact. The passages can be near or adjacent to contacts, such as signal and power contacts, on the tongue. Liquids that form a current path between the liquid-detect contact and another contact, such as a power supply contact or connection-detect contact, can be detected. 
     In these and other embodiments of the present invention, various mitigation strategies can be taken in response to the detection of a liquid in or on a connector. For example, a user can be alerted that liquid is present and that the device housing the connector should be powered down. A user can be alerted that the device is powering down and then the device can power down. The device can power down following the detection of the presence of liquid. Liquid ejection or cleaning techniques can be undertaken by the device or suggested to the user. Circuitry connected to one or more contacts of the connector can be disconnected. 
     In these and other embodiments of the present invention, it can be desirable to be able to detect the presence of an open or disconnect in the circuitry connected to a liquid-detect contact. Such an open or disconnect can provide a similar result as a liquid-free environment, thereby possibly giving a false-negative result. Accordingly, a loopback path for a loopback test can be provided. During loopback testing, the stimulus voltage signal (or a tracking voltage signal that follows the stimulus voltage signal) can be applied through an impedance to a first end or portion of the liquid-detect contact. A second end or portion of the liquid-detect contact can be connected to a loopback reference resistor. The detection of the loopback reference resistor can inform the system that a continuous path to and through the liquid-detect contact is present. 
     In these and other embodiments of the present invention, it can be desirable to be able to calibrate the liquid-detect circuitry. Accordingly, a calibration reference resistor having a known value can be provided. During calibration, the stimulus voltage signal (or a tracking voltage signal that follows the stimulus voltage signal) can be applied through an impedance to the calibration reference resistor. A measured resistance can be determined and compared to the expected value of the calibration reference resistor. The results of the comparison can be used to calibrate the liquid-detect circuitry. 
     In these and other embodiments of the present invention, it can be desirable to be able to protect the liquid-detect circuitry and associated circuits from high voltages caused by liquids in or on the connector. Accordingly, overvoltage circuits can be included and connected to the liquid-detect contact. These overvoltage circuits can control multiplexers connected to the liquid-detect contact. When an overvoltage condition is detected, the multiplexers can be switched to disconnect the liquid-detect circuitry from the liquid-detect contact. The multiplexers can further be connected to other circuit nodes or open circuits when an overvoltage condition is detected. 
     The presence of moisture, particularly in combination with the presence of an electric filed, can greatly accelerate the growth of dendrites between contacts. These dendrites can form conductive paths between contacts that can severely hamper the operation of circuits connected to the contacts. Also, a tongue of a connector can be formed of a printed circuit board supported by a metal frame. During insertion an extraction of a corresponding connector, metal fragments from the metal frame—as well as other conductive particulate matter—can accumulate around the liquid-detect contact. This can form or help to form—along with these dendrites—current paths from the liquid-detect contact. Accordingly, one or more raised surfaces formed of solder mask, glass deposition, or other layer can be positioned around the liquid-detect contact and one or more nearby contacts. The raised surfaces can help to prevent the buildup of dendrites and conductive matter around the liquid-detect contact, thereby helping to prevent the formation of current paths between contacts. 
     Embodiments of the present invention can provide liquid detection for various types of devices, such as portable computing devices, tablet computers, desktop computers, laptops, all-in-one computers, audio devices, wearable computing devices, cell phones, smart phones, media phones, storage devices, portable media players, navigation systems, monitors, power supplies, video delivery systems, adapters, remote control devices, chargers, and other devices. The liquid detection can be used in various connectors. These connectors can provide pathways for power and signals that are compliant with various standards such as one of the Universal Serial Bus (USB) standards including USB Type-C, High-Definition Multimedia Interface® (HDMI), Digital Visual Interface (DVI), Ethernet, DisplayPort, Thunderbolt™, Lightning®, Joint Test Action Group (JTAG), test-access-port (TAP), Directed Automated Random Testing (DART), universal asynchronous receiver/transmitters (UARTs), clock signals, power signals, and other types of standard, non-standard, and proprietary interfaces and combinations thereof that have been developed, are being developed, or will be developed in the future. 
     Various embodiments of the present invention can incorporate one or more of these and the other features described herein. A better understanding of the nature and advantages of the present invention can be gained by reference to the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates an electronic system that can be improved by the incorporation of an embodiment of the present invention; 
         FIG.  2    illustrates a tongue of a connector receptacle that can be improved by an embodiment of the present invention; 
         FIG.  3    illustrates connection detect circuitry that can be improved by the incorporation of an embodiment of the present invention; 
         FIG.  4    illustrates a connector tongue according to an embodiment of the present invention; 
         FIG.  5    illustrates a portion of a connection detect circuit according to an embodiment of the present invention; 
         FIG.  6    illustrates a connector tongue according to an embodiment of the present invention; 
         FIG.  7 A  and  FIG.  7 B  illustrate a connector tongue according to an embodiment of the present invention; 
         FIG.  8 A  and  FIG.  8 B  illustrate a connector tongue according to an embodiment of the present invention; 
         FIG.  9 A  illustrates a pulse waveform that can be applied to a liquid-detect contact according to an embodiment of the present invention,  FIG.  9 B  illustrates a simplified circuit model of a liquid that can be detected by an embodiment of the present invention, and  FIG.  9 C  illustrates possible resulting current and voltage waveforms that can be detected at a liquid-detect contact according to an embodiment of the present invention; and 
         FIG.  10    illustrates a simplified diagram of a liquid-detect circuit according to an embodiment of the present invention. 
     
    
    
     DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
       FIG.  1    illustrates an electronic system that can be improved by the incorporation of an embodiment of the present invention. This figure, as with the other included figures, is shown for illustrative purposes and does not limit either the possible embodiments of the present invention or the claims. 
     In this example, first electronic device  110  can be in communication with second electronic device  120  over a cable  130 . Specifically, connector insert  132  on cable  130  can be inserted into connector receptacle  112  on first electronic device  110 , while a second connector insert (not shown) can be inserted into a second connector receptacle (not shown) on second electronic device  120 . First electronic device  110  and second electronic device  120  can communicate by sending data to each other over cable  130 . First electronic device  110  and second electronic device  120  can share power over cable  130  as well. 
     Contacts  220  (shown in  FIG.  2   ) in connector receptacle  112  of first electronic device  110  and contacts (not shown) in connector insert  132  can be exposed to liquids, moisture, or other contaminants (again, collectively referred to as liquids.) These can corrode contacts  220  and contacts (not shown) in connector insert  132 . Accordingly, it can be desirable to be able to detect the presence liquid in connector receptacle  112  or connector insert  132 . Once the presence of a liquid is detected, mitigating steps can be performed by first electronic device  110  or suggested to a user. 
       FIG.  2    illustrates a tongue of a connector receptacle that can be improved by an embodiment of the present invention. Tongue  200  can include frame  210  supporting printed circuit board  230 . Tongue  200  can include a leading edge  202  and an electromagnetic interference (EMI) shield or ground pad  240 . A number of contacts  220  can be located on tongue  200  between leading edge  202 , frame  210 , and ground pad  240 . Contacts  220  can include power supply or VBUS contact  222  and VBUS contact  223 , transmit differential-pair contacts  224  and receive differential-pair contacts  225 , connection-detect contact  226 , sideband use contact  227 , and USB contacts  228 , in accordance with the USB Type-C specification. Frame  210  can serve as a ground contacts on each side of tongue  200 . Contacts  220  on the top surface of tongue  200  can be repeated on a bottom surface of tongue  200 , again in accordance with the USB Type-C specification. 
     Contacts  220  (or contacting portions of contacts  220 ) can be plated on printed circuit board  230 . When a liquid is present on tongue  200 , one or more contacts  220  can become damaged. This damage can be caused by be liquid causing electrical shorts among two or more of contacts  220 , frame  210 , or ground pad  240 . This damage can be exacerbated when it occurs between contacts at different voltage potentials. For example, liquid between VBUS contact  222  and connection-detect contact  226  can cause high currents to flow, thereby causing damage. Similarly, liquid between VBUS contact  222  and ground pad  240  can cause high currents to flow, again causing damage. Additionally, such liquids, particularly in the presence of a voltage potential, can greatly accelerate the formation of dendritic growth between these contacts. This dendritic growth can either increase the likelihood of electrical shorts between these contacts or cause permanent electrical shorts, thereby reducing or eliminating the functionality of connector receptacle  112  (shown in  FIG.  1   .) 
       FIG.  3    illustrates connection detect circuitry that can be improved by the incorporation of an embodiment of the present invention. As in  FIG.  1   , first electronic device  110  can be connected to second electronic device  120  through cable  130 . First electronic device  110  can include connection-detect contact  226  (referred to as a CC contact.) Connection-detect contact  226  can be connected through pulldown resistor  310  to ground, thereby indicating that first electronic device  110  is, or is configured as, a power-sink device. Connection-detect contact  226  can be connected to a corresponding contact in second electronic device  120  through conduit  138  in cable  130 , which can be connected to pull-up resistor  320  in second electronic device  120 . Pull-up resistor  320  can indicate that second electronic device  120  is, or is configured as, a power-source device. VBUS contact  222  (shown in  FIG.  2   ) can be adjacent to connection-detect contact  226 . The presence of a liquid between these contacts can cause current to flow from VBUS contact  222  to connection-detect contact  226 . This presence of a liquid can cause dendritic growth between VBUS contact  222  and connection-detect contact  226 . 
     Again, it can be desirable to be able to determine the presence of liquids between these and other contacts. More generally, it can be desirable to be able to determine the presence of liquid on or in a connector receptacle or connector insert. Examples of connector tongues with this capacity are shown in the following figures. While these examples are shown as being implemented on connector tongues, embodiments of the present invention can be employed on other portions of connector inserts and connector receptacles. 
       FIG.  4    illustrates a connector tongue according to an embodiment of the present invention. Tongue  400  can be used in connector receptacle  112  (shown in  FIG.  1   ), or in other connector receptacles or connector inserts according to embodiments of the present invention. Tongue  400  can include printed circuit board  430 . Printed circuit board  430  can be supported by frame  410 . Tongue  400  can include leading edge  402 . Tongue  400  can further include EMI shield or ground pad  440 . Printed circuit board  430  can support contacts  420 . Contacts  420  can include power supply or VBUS contact  422  and VBUS contact  423 , transmit differential-pair contacts  424  and receive differential-pair contacts  425 , connection-detect contact  426 , sideband use (SBU) contact  427 , and USB contacts  428 , in accordance with the USB Type-C specification. Frame  410  can serve as a ground contacts on each side of tongue  400 . Contacts  420  on the top surface of tongue  400  can be repeated on a bottom surface of tongue  400 , again in accordance with the USB Type-C specification. 
     Tongue  400  can further include liquid-detect contact  450 . A corresponding liquid-detect contact (not shown) can be located on an opposing side of tongue  400 . Liquid-detect contact  450  can be positioned in such a way that connections to contacts in the corresponding connector insert  132  (shown in  FIG.  1   ) are limited to transient and incidental encounters. During liquid detection mode, liquid-detect contact  450  can convey an applied voltage signal. When a liquid is present on liquid-detect contacts  450 , the presence of the applied voltage signal can cause a current to flow through liquid-detect contact  450 . If liquid is solely present on liquid-detect contact  450 , small charging currents can flow into the liquid itself. When liquid is present between liquid-detect contact  450  and a second contact, such as VBUS contact  422  or ground pad  440 , larger currents can flow. These currents can thus be used to determine the presence of a liquid on tongue  400 . The magnitude and phase relationship of currents flowing through liquid-detect contact  450  can provide information regarding the nature and extent of the liquid. Further details are shown below in  FIG.  9    in  FIG.  10   . 
     In these and other embodiments of the present invention, liquid-detect contact  450  might not have a corresponding contact in corresponding connector insert  132  (shown in  FIG.  1   .) In these and other embodiments of the present invention, liquid-detect contact  450  can have a corresponding contact in connector insert  132 . This can enable liquid-detect circuitry, such as liquid-detect circuitry  1000  shown in  FIG.  10    below, to be able to detect the presence of moisture in connector insert  132  even in the absence of moisture in connector receptacle  112  itself. In these and other embodiments of the present invention, the functionality of one or more contacts  420  can be multiplexed in time or frequency with the function of liquid-detect contact  450 , thereby allowing the removal or repurposing (either temporarily or permanently) of liquid-detect contact  450 . 
       FIG.  5    illustrates a portion of a connection detect circuit according to an embodiment of the present invention. In this example, first electronic device  110  can connect to second electronic device  120  through cable  130 . Connection-detect contact  426  can be connected through pulldown resistor  310  to ground. Alternatively, connection-detect contact  426  can be disconnected from pulldown resistor  310  by multiplexer  510 , for example when liquid is detected in connector receptacle  112  of first electronic device  110 . Connection-detect contact  426  can be connected to a corresponding connection-detect contact  526  and pull-up resistor  320  in second electronic device  120  through conduit  138 . In these and other embodiments of the present invention, a multiplexer (not shown) that is the same as or similar to multiplexer  510  can be used to disconnect pull-up resistor  320  from connection-detect contact  526  in second electronic device  120  when liquid is detected in the connector receptacle (not shown) of second electronic device  120 . 
     In these and other embodiments of the present invention, it can be desirable to disconnect connection-detect contact  426  from circuitry internal to first electronic device  110 . This disconnection can reduce or eliminate the electric field or potential between connection-detect contact  426  and adjoining or nearby contacts. This disconnection can reduce or prevent undesired current flow through a liquid from a nearby or adjoining contact. For example, disconnecting connection-detect contact  426  from pulldown resistor  310  can help to eliminate or reduce an undesired current flow from VBUS contact  422  to connection-detect contact  426 . This disconnection can also prevent second electronic device  120  from attempting to charge first electronic device  110 , again reducing current flow and electric fields and potentials. 
     Again, liquid in connector receptacle  112  (shown in  FIG.  1   ) can cause dendritic growth between and among contacts  420 , liquid-detect contact  460 , and ground pad  440 . Also, in these and other embodiments of the present invention, frame  410  can be formed of metal, such as titanium. Frame  410  can be manufactured using metal injection molding or other manufacturing techniques. As connector insert  132  (shown in  FIG.  1   ) is repetitively inserted and withdrawn from connector receptacle  112 , portions of frame  410  can become scraped, thereby creating small grains or pieces of conductive material. These and other pieces of particulate matter, including conductive material, can accumulate in one or more areas on a surface of tongue  400 . For example, this conductive material can accumulate among contacts  420 , between contacts  420  and liquid-detect contact  450 , or between liquid-detect contact  450  and ground pad  440 . In order to prevent or reduce dendritic growth as well as this accumulation of conductive material, embodiments of the present invention can include one or more protective structures. An example is shown in the following figure. 
       FIG.  6    illustrates a connector tongue according to an embodiment of the present invention. Tongue  600  can be utilized in connector receptacle  112  (shown in  FIG.  1   ), or in other connector receptacles or connector inserts according to embodiments of the present invention. Tongue  600  can include printed circuit board  630 . Printed circuit board  630  can be supported by frame  610 . Tongue  600  can include leading edge  602 . Printed circuit board  630  can support contacts  620 . Contacts  620  can include power supply or VBUS contact  622  and VBUS contact  623 , transmit differential-pair contacts  624  and receive differential-pair contacts  625 , connection-detect contact  626 , sideband use contact  627 , and USB contacts  628  in accordance with the USB Type-C specification. Frame  610  can serve as a ground contacts on each side of tongue  600 . Contacts  620  on the top surface of tongue  600  can be repeated on a bottom surface of tongue  600 , again in accordance with the USB Type-C specification. As before, a liquid-detect contact, liquid-detect contact  650 , can be included. Liquid-detect contact  650  can be positioned between contacts  620  and ground pad  640 . A corresponding liquid-detect contact (not shown) can be located on an opposing side of tongue  600 . 
     Again, dendritic growth can occur between and among contacts  620 , between contacts  620  and liquid-detect contact  650 , between liquid-detect contact  650  and ground pad  640 , or elsewhere on or near tongue  600 . Additionally, conductive material can accumulate in these areas. Accordingly, dams or raised surfaces  660  can be located around one or more contacts  620 . For example, raised surfaces  660  can be located around VBUS contact  622  and connection-detect contact  626 . Raised surfaces  660  can help to prevent dendritic growth and accumulation of conductive material between VBUS contact  632  and connection-detect contact  626 . Raised surfaces  660  can further help to prevent dendritic growth and the accumulation of conductive material between VBUS contact  622  and liquid-detect contact  650 , as well as between connection-detect contact  626  and liquid-detect contact  650 . Raised surface  662  can be positioned between liquid-detect contact  650  and ground pad  640 . Raised surface  662  can similarly help to prevent dendritic growth and the accumulation of conductive material between liquid-detect contact  650  and ground pad  640 . 
     Raised surfaces  660  and raised surface  662  can be formed in various ways. For example, raised surfaces  660  and raised surface  662  can be formed of a solder mask, glass deposition, or other layer. Alternatively, raised surfaces  660  and raised surface  662  can be recessed surfaces. One or more of raised surfaces  660  and raised surface  662  can be located on an opposing side (not shown) of tongue  600 . 
     In the above examples of the present invention, tongue  400  and tongue  600  can be formed of a printed circuit board surrounded by a metallic frame. In these and other embodiments of the present invention, tongues can be formed in various ways. For example, a tongue can be formed of a molded portion. This molded portion can be supported by a frame. This frame can be a metallic frame. Also, in the example of  FIG.  4   , liquid-detect contact  450  can be positioned in such a way that connections to contacts in the corresponding connector inserts  132  (shown in  FIG.  1   ) are limited to transient and incidental encounters. In these and other embodiments of the present invention, a liquid-detect contact can be located in different positions. An example is shown in the following figure. 
       FIG.  7 A  and  FIG.  7 B  illustrate a tongue for a connector receptacle according to an embodiment of the present invention. Tongue  700  can be used in connector receptacle  112  (shown in  FIG.  1   ), or in other connector receptacles or connector inserts according to embodiments of the present invention.  FIG.  7 B  is a cross-section of tongue  700  in  FIG.  7 A  taken along cutline A-AA. Tongue  700  can include leading edge  702 . Tongue  700  can include molded portion  770 . Molded portion  770  can be supported by frame  710 . Molded portion  770  can support contacts  720 . Contacts  720  can include power supply or VBUS contact  722  and VBUS contact  723 , transmit differential-pair contacts  724  and receive differential-pair contacts  725 , connection-detect contact  726 , sideband use contact  727 , and USB contacts  728 , in accordance with the USB Type-C specification. Frame  710  can serve as a ground contacts on each side of tongue  700 . Contacts  720  on the top surface of tongue  700  can be repeated on a bottom surface of tongue  700 , again in accordance with the USB Type-C specification. Molded portion  770  can itself be partially over-molded by molded portion  730 . 
     In this example, contacts  720  can be stamped contacts that extend from tongue  700  further into first electronic device  110 . This arrangement can make the positioning of a liquid-detect contact different as compared to the arrangement for liquid-detect contact  450  on tongue  400  and liquid-detect contact  650  on tongue  600  above. Accordingly, these and other embodiments of the present invention can include liquid-detect contact  750  in a center of tongue  700 , that is, between frame  710 , leading edge  702 , and ground pad  740 , as well as between contacts  720  on a top and bottom surface of tongue  700 . 
     In these and other embodiments of the present invention, one or more passages  760  can be included through molding portions  770 . These passages  760  can provide passages for liquids to reach liquid-detect contact  750  so that they can be detected. In these and other embodiments of the present invention, passages  760  can be sufficient in size to avoid the effects of surface tension, which could otherwise prevent liquid from reaching liquid from reaching liquid-detect contact  750 . 
     Liquid-detect contact  750  can be formed by dividing a central ground plane into different sections. For example, a central ground plane can be divided into liquid-detect contact  750 , ground plane  780 , and ground plane  790 . Ground plane  780  can help to isolate signals on differential-pair contacts  725  from corresponding contacts (not shown) on a bottom surface of tongue  700 . Similarly, ground planes  790  can help to isolate signals on differential-pair contacts  724  from corresponding contacts (not shown) on a bottom surface of tongue  700 . These structures are shown further in the following figure. 
       FIG.  8 A  and  FIG.  8 B  illustrate a tongue of a connector receptacle according to an embodiment of the present invention.  FIG.  8 B  is a cross-section of tongue  700  in  FIG.  8 A  taken along cutline B-BB. In this example, liquid-detect contact  750 , ground plane  780 , and ground plane  790  are shown. Again, tongue  700  can include molded portion  770  and molded portion  730 . Molded portion  730  can be an overmolded portion that is formed over front edges of contacts  720  (shown in  FIG.  7 A  and  FIG.  7 B .) Passages  760  can extend from a surface of molded portion  770  to a surface of liquid-detect contact  750 . Ground plane  780  can help to isolate signals on differential-pair contacts  725  from corresponding contacts (not shown) on a bottom surface of tongue  700 . Similarly, ground planes  790  can help to isolate signals on differential-pair contacts  724  from corresponding contacts (not shown) on a bottom surface of tongue  700 . Various features, including passages  760 , can be repeated on the opposing side of tongue  700 . 
     In these and other embodiments of the present invention, a signal, such as a voltage signal, can be applied to liquid-detect contacts, such as liquid-detect contact  450 , liquid-detect contact  650 , or liquid-detect contact  750 . A resulting current can be measured, and from the magnitude and relative phase of the resulting current, a determination as to the presence of a liquid can be made. In these and other embodiments of the present invention, the voltage signal can be a sinewave. When the voltage signal is a sinewave, electrochemical impedance spectroscopy (EIS) techniques can be used. The sinewave can have a frequency of 90 Hz, 100 Hz, 110 Hz, 120 Hz, 200 Hz, or other frequency. 
     Alternatively, other voltage signals can be applied to a liquid-detect contact consistent with embodiments of the present invention. For example, pulse waveforms, square-waves, impulse functions, saw-tooth waveforms, and other types of voltage signals can be applied. An example is shown in the following figure. 
       FIG.  9 A  illustrates a pulse waveform that can be applied to a liquid-detect contact according to an embodiment of the present invention. In this example, after an initial time T1, a voltage pulse  922  having a duration δ 1  can be can be provided as a stimulus, where voltage pulse  922  is shown as a function of voltage amplitude on axis  920  and time on axis  910 . A corresponding current pulse  942  can result. In this example, current pulse  942  can similarly have a duration δ 1 , and is shown as a function of current on axis  940  and time on axis  930 . 
       FIG.  9 B  illustrates a simplified circuit model of a liquid that can be detected by an embodiment of the present invention. Simplified circuit model  950  can include a parallel combination of resistor RP and capacitor CP in series with series resistance RS. The absolute and relative values of these components can vary depending on the amount and type of liquid, if any, is present and in contact with a liquid-detect contact, such as liquid-detect contact  450  (shown in  FIG.  4   ), liquid-detect contact  650  (shown in  FIG.  6   ), or liquid-detect contact  750  (shown in  FIG.  7 A .) 
       FIG.  9 C  illustrates possible resulting current and voltage waveforms that can be detected at a liquid-detect contact according to an embodiment of the present invention. In this example, current pulse  972  having a duration δ 1  can be the result of voltage pulse  922  (shown in  FIG.  9 A ) and is shown as a function of current amplitude on axis  970  and time on axis  960 . Current pulse  972  can have an overshoot  974  and can settle to a value  976  following an exponential decay. Current pulse  972  can also include undershoot  978 , which can settle to zero following an exponential decay. Voltage pulse  922  can have a duration δ 1  and can also be the result of voltage pulse  922  and is shown as a function of voltage amplitude on axis  990  and time on axis  980 . Voltage pulse  992  can have a rising edge  994  that follows RC time constant and can reach a peak  996  before decaying to zero. 
     When pulses are used as a stimulus voltage signal, these various characteristics, such as overshoot  974 , rising edge  994 , and others, can be used to determine the presence or absence of liquid. When sinewaves are used, various characteristics, such as the amplitude and phase of any resulting current, can be used to determine the presence or absence of liquid. In these and other embodiments of the present invention, the absence, presence, and relative amount of liquid can be determined using these various characteristics. Further, information about the type of liquid can also be determined using these various characteristics. In these and other embodiments of the present invention, different algorithms can use these characteristics when different tongues, such as tongue  400  (shown in  FIG.  4   ) and tongue  700  (shown in  FIG.  7   ) are used. 
       FIG.  10    illustrates a simplified diagram of a liquid-detect circuit according to an embodiment of the present invention. Liquid-detect circuitry  1000  can perform several tasks. For example, liquid-detect circuitry  1000  can provide a signal to a liquid-detect contact and measure a resulting current. Liquid-detect circuitry  1000  can further perform self-diagnostic tests. These self-diagnostic tests can include a loopback test and a self-calibration test. In these and other embodiments of the present invention, liquid detection can be performed using other contacts. For example, liquid detection can be performed using USB or SBU contacts. 
     To perform liquid detection at liquid-detect contact  450 , liquid-detect circuitry  1000  can apply a voltage signal to liquid-detect contact  450  and measure a resulting current. Specifically, first logic circuit  1010  can generate a signal on line  1012 . First logic circuit  1010  can generate this signal using pulse density modulation (PDM), or other technique. The signal on line  1012  can approximate a sinewave, or can be another type of signal, such as a pulse, a series of pulses, a saw-tooth waveform, or other type of waveform. Alternatively, a DAC (not shown), such as a high-resolution DAC, can be used to generate a sinewave or other type of waveform. Filter amplifier  1020 , along with resistors R 1  and R 9 , and capacitors C 1  and C 2 , can filter the waveform on line  1012  to generate a stimulus voltage signal. Filter amplifier  1020  and its associated components can be particularly useful when the signal on line  1012  is a sinewave in order to achieve a desired spectral purity. When the signal on line  1012  is a pulse or other type of waveform, some or all of filter amplifier  1020  and its associated components can be bypassed, for example with a switch (not shown.) 
     The stimulus voltage signal at the output of filter amplifier  1020  can be provided on line  1042  to analog-to-digital converter  1040 . The stimulus voltage signal at the output of filter amplifier  1020  can further be provided to a noninverting input of transimpedance amplifier  1030 . In this configuration, the inverting input of transimpedance amplifier  1030  can track the non-inverting input of transimpedance amplifier  1030 , thereby tracking the stimulus voltage signal at the output voltage of filter amplifier  1020 . This tracking signal voltage can be applied through resistor R 2  and switch  1057  to liquid-detect contact  450  at location  452  as the applied signal voltage. Current flow into liquid-detect contact  450  can be provided through input resistor R 2  and feedback resistor R 3  of transimpedance amplifier  1030 . This can generate a measured voltage signal at the output of transimpedance amplifier  1030  on line  1044 . This measured voltage signal is thus reflective of the current flowing through liquid-detect contact  450 . This measured voltage signal can be converted by analog-to-digital converter  1040 . 
     In this way, analog-to-digital converter  1040  can sample a stimulus voltage signal on line  1042 . Analog-to-digital converter  1040  can further sample a measured voltage signal on line  1044  that tracks a current flowing through liquid-detect contact  450 . In this way, the magnitude of the current flowing through liquid-detect contact  450  and its phase relationship to the stimulus voltage signal on line  1042  can be determined. This information can this be used to determine the presence of liquid in connector receptacle  112  (shown in  FIG.  1   ) that houses tongue  400 . 
     In these and other embodiments of the present invention, various mitigation strategies can be taken in response to the detection of a liquid in or on a connector. For example, a user can be alerted that liquid is present on tongue  400  and that first electronic device  110  (shown in  FIG.  1   ) should be powered down. A user can be alerted that first electronic device  110  is powering down and then first electronic device  110  can power down. First electronic device  110  can power down following the detection of the presence of liquid. Liquid ejection or cleaning techniques can be undertaken by the device or suggested to the user. Circuitry connected to one or more contacts  420  (shown in  FIG.  4   ) can be disconnected. 
     Liquid detection can occur at various times. For example, liquid-detect measurements can occur continuously. Liquid-detect measurements can occur continuously when a device is being used. Liquid-detect measurements can occur periodically whether or not the device is being used. Liquid-detect measurements can occur periodically when the device is being used. Liquid-detect measurements can occur following an event, such as a fall that is detected using an accelerometer in the device. Liquid-detect measurements can occur following a power-up of the device. Liquid-detect measurements can occur following the start of a power-down of the device. Liquid-detect measurements can occur at any combination of these or other times. 
     When liquid-detect measurements are occurring, switch  1056  can connect resistor R 4  to resistor R 6  via line  1014 . In this way, resistor R 4  can pull down the voltage on line  1014 , and in response first logic circuit  1010  can determine that measurements are taking place. Also in this state, switch  1057  can connect R 2  to liquid-detect contact  450  at location  452 . Switch  1066  can connect location  454  of liquid-detect contact  450  to an open circuit. Similarly, resistor R 7  and resistor R 8  can be connected to an open circuit through switch  1067 . 
     In these and other embodiments of the present invention, it can be desirable to ensure that liquid-detect circuitry  1000  is correctly connected to liquid-detect contact  450  on tongue  400 . If an inadvertent disconnection were to occur, the presence of a liquid at liquid-detect contact  450  went go undetected. Accordingly, embodiments of the present invention can provide a loopback path to determine that the necessary connections for liquid detection are intact. 
     During a loopback path test, a voltage can again be applied through resistor R 2  to liquid-detect contact  450  at location  452 . Location  454  of liquid-detect contact  450  can be connected to location  452  through liquid-detect contact  450  and can be connected through switch  1066  to resistor R 5 . Resistor R 5  can be a resistor having a known value and a known temperature coefficient. Resistor R 5  can draw an expected current through resistors R 2  and R 3  of transimpedance amplifier  1030 . When the expected current (given the circuit&#39;s temperature) is measured, it can be determined that the liquid-detect circuitry is correctly connected to liquid-detect contact  450 . While tongue  400  is shown in this example, other tongues, such as tongue  600  (shown in  FIG.  6   ) and tongue  700  (shown in  FIG.  7   ), can be similarly used with liquid-detect circuitry  1000 . 
     In these and other embodiments of the present invention, it can be desirable to calibrate the liquid-detect circuitry. During calibration, resistor R 4  can be connected to input resistor R 2  through switch  1056 . Resistor R 4  can be a known resistor having a known temperature coefficient. This known resistor can draw a current that can be measured and compared to an expected current, given the circuit&#39;s temperature. The liquid detection circuitry can be calibrated based on this comparison. 
     In these and other embodiments of the present invention, it can be desirable to perform liquid detection at other contacts. To do so, resistor R 2  can be connected to resistors R 7  and R 8  through switch  1067 . Resistors R 7  and R 8  can be further connected either to USB contacts  428  or SBU contacts  427  through multiplexer  1070 . In this configuration, resistor R 2  can be disconnected from liquid-detect contact  450  by switch  1057 . 
     In these and other embodiments of the present invention, switch  1056  and switch  1057  in multiplexer  1050  can be controlled by logic  1054 . Similarly, switch  1066  and switch  1067  in multiplexer  1060  can be controlled by logic  1064 . Logic  1054  and logic  1064  can be controlled by second logic circuit  1080 . 
     In these and other embodiments of the present invention, various contacts, such as liquid-detect contact  450 , can be exposed to overvoltage conditions. When an overvoltage condition is detected, these contacts can be disconnected from the liquid-detect circuitry. For example, an overvoltage condition at switch  1056  or switch  1057  in multiplexer  1050  can be detected by overvoltage circuitry  1052 . Overvoltage circuitry  1052  can then respond accordingly. For example, overvoltage circuitry  1052  can connect liquid-detect contact  450  to an open circuit via switch  1057 . Similarly, an overvoltage condition at switch  1066  or switch  1067  in multiplexer  1060  can be detected by overvoltage circuitry  1062 . Overvoltage circuitry  1062  can then respond accordingly. For example, switch  1066  in multiplexer  1060  can connect liquid-detect contact  450  to an open circuit via switch  1066 . Lines  1072  can be connected to an open circuit via switch  1067 . In these and other embodiments of the present invention, multiplexer  1050  and multiplexer  1060  can connect their respective switches to other circuit nodes or open circuits following the detection of an overvoltage condition. 
     Embodiments of the present invention can provide liquid detection for various types of devices, such as portable computing devices, tablet computers, desktop computers, laptops, all-in-one computers, wearable computing devices, audio devices, cell phones, smart phones, media phones, storage devices, portable media players, navigation systems, monitors, power supplies, video delivery systems, adapters, remote control devices, chargers, and other devices. The liquid detection can be done in various types of connectors. These connectors can provide pathways for power and signals that are compliant with various standards such as one of the Universal Serial Bus (USB) standards including USB Type-C, High High-Definition Multimedia Interface® (HDMI), Digital Visual Interface (DVI), Ethernet, DisplayPort, Thunderbolt™, Lightning®, Joint Test Action Group (JTAG), test-access-port (TAP), Directed Automated Random Testing (DART), universal asynchronous receiver/transmitters (UARTs), clock signals, power signals, and other types of standard, non-standard, and proprietary interfaces and combinations thereof that have been developed, are being developed, or will be developed in the future. 
     The above description of embodiments of the invention has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form described, and many modifications and variations are possible in light of the teaching above. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. Thus, it will be appreciated that the invention is intended to cover all modifications and equivalents within the scope of the following claims.