Pushbutton circuit for vehicle electric devices - has pushbuttons divided into groups, each forming voltage divider with series connected resistor actuated by own transistor

摘要

The push-button circuit consists of push-buttons coupled in parallel, via staged resistors in series, to form a group which is connected via transistor (28, 29) to a shared resistor (22). This forms a voltage divider connected to the supply. The divider tapping produces a signal voltage. The switching states of the push-buttons are interrogated by a microprocessor, using clock pulses at the control input of the transistor. The signal voltage at the divider tapping is also measured. The signal volrage is fed to the microprocessor which then initiates the appropriate switching step via a decoder(25). The switching paths of the push-button groups preferably lie at the divider tap via a transistor switching path behind the common resistor. The decoder may contain cyclically energised amplifier stages (33, 34), with outputs coupled each to a transistor control path.