Ab Electronic Components Limited

Derek M Embrey

Stuart F Webb

Ian J Bickford

Graham J Legg

Argus F Caxton Doss-Desouza

In order to provide a lamp failure warning in both illuminated and unilluminated states of the lamp, there is provided a resistance bridge circuit Rs, L, R2 and R3 which is substantially in balance if the lamp L is sound. An amplifier IC1 acts as a detection means if the bridge goes out of balance as a consequence of failure of the lamp L. In the unilluminated state a reduced current is fed to the bridge via a high value resistance R1, which is by-passed by a lamp switch SW1 if the lamp is to receive enough power to illuminate it.

Lamp monitoring circuit

In order to provide a reliable position indicator for a gear control, particularly for automatic transmission motor vehicles, use is made of reed switches (2). These may be mounted in a sealed housing and operable by a magnet (1) from outside the housing. The magnet (1) is movable by and with the gear control. The reed switches (2) may be mounted on a printed circuit board (3) and flux concentrators (4) are preferably provided between adjacent reed switches (2) to shield them until the magnet (1) is closely adjacent.

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Lisvane, United Kingdom

Derek M Embrey