| 摘要 |
PURPOSE:To generate an hour informing sound with the use of a simple construction by controlling a switching circuit which is connected with an audible sound signal source through a time constant circuit to be supplied with a display element driving voltage. CONSTITUTION:A switching transistor TR1 is rendered inconductive ten minutes before each hour and conductive at each hour through a time constant differential circuit, which has its time constant determined by capacitors C1, R1 and R2, by the drive voltage of the segment b of a 10 minute digital display unit 2c, which is to be impressed upon a terminal A. As a result, the charges in a capacitor C2 are instantly relased through the transistor TR1 being conductive to render a transistor TR2 inconductive at each correct hour. Then, the potential at a terminal C becomes substantially the same as an audio sound signal source voltage B so that the hour informing sound which is gradually attenuated is generated without any error at each correct hour with the use of a simple construction by the action of the transistor TR1 which is rendered conductive at a transient time according to the time constant of a differential circuit through the oscillatory circuit. |
