Abstract: The invention relates to electronic warning devices. The control system includes means for supplying an accurate clock signal and a divider (CD1, CD2) for dividing the clock signal to obtain an audio frequency, adjusting the mark/space ratio of the audio frequency for application to a power transistor (T6), said transistor driving a loudspeaker (HP), providing a cyclic modulation for modulating the clock frequency; and timing the duration of the sound emission of the loud speaker. The timing functions can all be provided without the use of electrolytic capacitors as would otherwise have been necessary, thereby avoiding problems due to the lack of precision and drift in the values of such capacitors.

Abstract: A device for controlling the charging and discharging of a storage battery has an input to which there is applied an input voltage proportional to the magnitude and sign of the current flowing through the battery. The input voltage is amplified and integrated to provide an integral which is an image of the state of charge of the battery. In this invention the input voltage is converted to a pulse train whose frequency is proportional to the magnitude of the input voltage and the pulses are added or subtracted according to its sign. The pulse total forms the said image of the state of charge of the battery.