Abstract: When heat cooking of food placed in a heating chamber of a microwave oven is started, smell given out of the food is detected and a cooking sequence program suitable for the kind of the food is automatically selected based on the information of the detected smell. Heat cooking of the food is carried out thereafter following the selected cooking sequence program. In parallel with this heat cooking, the smell given out of the food is detected to detect fire of the food based on the information of the detected smell. When fire of the food is detected, heating of the food is immediately interrupted, thereby preventing damage to the oven which is caused by abnormally high temperature in the heating chamber, while preventing further browning of the food.

Abstract: A microwave oven includes a piezo-electric speaker for audible announcement purposes and a microcomputer for controlling operations of the microwave oven. The mocrocomputer always develops a frequency signal for activating the piezo-electric speaker. A gate signal is developed from the microcomputer so that the gate signal and the frequency signal are commonly applied to the base electrode of a switching transistor. When the gate signal bears the logic "L", the switching transistor repeats the ON/OFF operation in response to the frequency signal applied thereto. The piezo-electric speaker is connected to the switching transistor, whereby the piezo-electric speaker generates the sound whenever the gate signal bears the logic "L".

Abstract: A plurality of heater elements are heated using a DC voltage to render the display brightness of a fluorescent indicator tube uniform. A circuit comprises a first circuit for intermittently applying a heater current to the indicator tube at a predetermined interval, and a second circuit for preventing the indicator tube from developing a display during heating the heater elements.