A method can be used for operating an optoelectronic proximity sensor. The proximity sensor includes a radiation-emitting component, a radiation-detecting component and a control unit. The radiation-emitting component is operated by means of a pulsed current. During each measurement period, the pulsed current of the radiation-emitting component has an on-time and an off-time. The pulsed current has a pulse current intensity during the on-time, and the control unit evaluates a detector signal of the radiation-detecting component and lowers the pulse current intensity for a subsequent measurement period, when the detector signal exceeds a threshold value during at least one measurement period.

An optical keypad for use in hazardous areas and which can ensure safe and reliable detection of keystrokes through an at least 8 mm thick glass window, as is required for electronics equipment located in hazardous explosive areas (In accordance with ATEX Directive 94/9/EC and similar requirements) is obtained by providing a system in which at least 6 LEDs are lit in a pseudo-random sequence, modulated by a pseudo-random frequency and the interval between the lighting of each of the LEDs is change randomly to avoid interference between collocated keypads and light from other sources, such as daylight and artificial light.

A keyboard system comprises a key structure including a key switch with a lighting element and phototransistor, and one or more processors that drive the lighting element for a first pulse duration. The output of the phototransistor is determined at the end of the first pulse duration, wherein the key structure is determined to be pressed when the output is below a first output value at an end of the first pulse duration, and unpressed when the output of the phototransistor is above a second output value at the end of the first pulse duration. A fall-time of the output during the first pulse duration is determined and the first pulse duration is calibrated to a second pulse duration when the fall time less than the first pulse duration, the second pulse duration being greater than the fall time and less than the first pulse duration.

A keyboard system comprises a key structure including a key switch with a lighting element and phototransistor, and one or more processors that drive the lighting element for a first pulse duration. The output of the phototransistor is determined at the end of the first pulse duration, wherein the key structure is determined to be pressed when the output is below a first output value at an end of the first pulse duration, and unpressed when the output of the phototransistor is above a second output value at the end of the first pulse duration. A fall-time of the output during the first pulse duration is determined and the first pulse duration is calibrated to a second pulse duration when the fall time less than the first pulse duration, the second pulse duration being greater than the fall time and less than the first pulse duration.

A keyboard system comprises a key structure including a key switch with a lighting element and phototransistor, and one or more processors that drive the lighting element for a first pulse duration. The output of the phototransistor is determined at the end of the first pulse duration, wherein the key structure is determined to be pressed when the output is below a first output value at an end of the first pulse duration, and unpressed when the output of the phototransistor is above a second output value at the end of the first pulse duration. A fall-time of the output during the first pulse duration is determined and the first pulse duration is calibrated to a second pulse duration when the fall time less than the first pulse duration, the second pulse duration being greater than the fall time and less than the first pulse duration.