Patent ID: 8437488

Claim:
A hearing instrument comprising an openable cover lid, the cover lid comprising at least one electrical input element, at least one lid contact terminal arranged to physically and electrically contact at least one corresponding device contact terminal when the lid is in a closed position, and an input arrangement for an electronic circuit, characterised in that the cover lid comprises at least two electrical input elements, each of the at least two input elements being functionally associated with the impedance between the lid contact terminal and a further terminal, the hearing instrument comprises means to infer the state of the input elements from said impedance, and the input arrangement comprises: a first input line and a second input line, a first switch and a second switch, wherein the first switch being configured to connect, in a closed position, the first input line to a common reference voltage, the second switch being configured to connect, in a closed position, the second input line to the common reference voltage, and the first and second switch being arranged such that during normal operation of the circuit at most one of them is in the closed position, a third switch arranged to connect, in a closed position, the first input line with the second input line, a first pull circuit configured to pull, when it is activated, the voltage of the first input line to a first reference voltage, and to pull, when it is not activated, the voltage of the first input line to a voltage different from the first reference voltage, and a second pull circuit configured to pull, when it is activated, the voltage of the second input line to a second reference voltage, and to pull, when it is not activated, the voltage of the second input line to a voltage different from the second reference voltage, and a status evaluation logic configured to determine the status of the third switch by repeatedly activating, for first time periods, the first pull circuit and, for second time periods, the second pull circuit and by determining, during the first time periods, the voltage of the second input line, and, during the second time periods, the voltage of the first input line, and by indicating that the third switch is closed either, if and only if said voltages both are substantially equal to the common reference voltage, with the first and second reference voltage being equal to the common reference voltage, or, if during the first time periods, a signal on the second input line corresponds to a signal determined by the first pull circuit, or, if during the second time periods, a signal on the first input line corresponds to a signal determined by the second pull circuit.