US Patent 10184909 Connection and corrosion detection

Methods, structures, and apparatus that are able to detect the presence of a connection to a device contact of an electronic device and are also able to detect the presence of contamination at the device contact. A host device includes a connection detection circuit and a contamination detection circuit connected to the device contact. The connection detection circuit includes a pull-up resistor that is pulled down by a pull-down resistor in an accessory device following a connection. The contamination detection circuit includes a current source to provide a current at the device contact and measurement circuitry to measure a resulting voltage.