Abstract: An electronic circuit (50) for receiving and discriminating modulated light of a specific modulation frequency or within a specific modulation frequency range includes a photodiode detector (52) responsive to light incident thereto for generating an electric current signal. A controllable shunt (54) is connected in parallel with the photodiode detector (52) and is controllable between a first operational mode in which the current is shunted, and a second operational mode in which the current is not shunted. A control circuit (56) is connected to the photodiode detector (52) and the shunt (54) for controlling the controllable shunt (54) into (a) the first operational mode, provided that the current signal does not include a signal of the specific modulation frequency or within the specific modulation frequency range, or (b) the second operational mode, provided that the current signal includes a signal of the specific modulation frequency or within the specific modulation frequency range.

Abstract: An information system comprises a master station (2, 10) controlling information to be displayed on a number of information units (30, 40) arranged remotely from said master station. The master station broadcasts instructions by modulated infrared signals, and these signals are detected by a photodiode within each information unit (30, 40), said information unit also comprising a receiver and logic circuitry. The information unit (30, 40) further comprises an emitter diode in order that it is capable of acknowledging the receipt of instructions. Information is presented on LCD-type displays, e.g. digits, a graphic field, or other information fields, all being implemented in LCD-type displays. The display units are, in particular, applicable in shops or warehouses, e.g. supermarkets, where a display unit may be arranged adjacent each item of merchandise, serving the purpose of displaying e.g. the unit price on the information unit.