Acoustic signalling circuit for cooker - has switch applying mains volts to NTC resistor in series with buzzer so sound increases gradually

摘要

The circuit consists of an NTC resistor (8) in series with a signalling device (6). The resulting series combination can be connected to the main supply via a change-over switch (4). The latter connects either this series combination or the heating element (2) to the supply. The change-over switch is operated when a given temp. is reached, e.g. when water has boiled. The current through the signalling device, e.g. a buzzer, gradually increases so that the sound liewise gradually increases. Alternatively, a PTC resistor may be connected in parallel with the buzzer and the parallel combination connected via a ballast resistor and the change-over switch to the mains. The effect on the buzzer's sound is the same as before.