Volume gradual sound sleep wake-up circuit

Car Audio Crystal 3.2*2.5mm 3225 24M (24.000MHZ) 20PF 10PPM 20PPM 30PPM

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The gradual sleep wake-up device is used together with the electronic alarm clock. When the set time of the alarm reaches a predetermined time, the wake-up power supply is turned on by the switch, so that the wake-up device wakes up the owner at a lower volume. After a certain amount of time, the volume of the wake-up device is increased to the maximum. This setting allows the owner to be protected from being scared when they are woken up.
The circuit consists of three parts: a monostable delay circuit, a controllable electronic switch and an audio oscillator. ICl and Cl, Rl form a monostable delay circuit, as the timing control circuit of the first stage volume.
When the electronic alarm clock arrives at the timing, the alarm switch is closed, and the working power of the volume gradual sleep wake-up device is turned on. At this time, the monostable delay circuit enters the delay process. At the beginning of the power-on, the 9V power supply is applied to Cl. Since the voltage across the capacitor cannot be abruptly changed, the negative voltage of Cl is almost as high as the positive pole, so that the NE555's 3 pin outputs a low level, and the VD is reverse biased. As of cutoff, the monostable circuit enters the transient steady state delay process. At this time, Cl is charged by Rl. When Cl is charged to lower the anode voltage to Voo /3, NE555 outputs a high level, and VD is turned on to apply a high level to the VT substrate.
While the power is turned on to bring the monostable circuit into the delay process, the power supply also divides the voltage to the base of the VT through the voltage division of R2 and R3, so that the VT enters the conduction state. Due to the addition to VT, the VT is in an amplified state and its emitter output voltage is low. Since the operating voltage supplied to the audio oscillator is low, the volume emitted is small.
When the monostable circuit delays, the ICl outputs a high level, which is approximately equal to the supply voltage of 9V. This voltage is applied directly to the base of the VT through VD, bringing the VT into saturation. Since the saturation voltage drop of the transistor is only about 0.3V, the voltage applied to the audio oscillator is close to 9V, which makes the audio oscillator emit a louder power. An audio oscillator consisting of IC2, R4, R5, and C3. Since the oscillation frequency of the oscillating circuit is off from the supply voltage, the oscillator output frequency remains unchanged in both phases. However, the output volume is related to the power supply voltage, and a high power supply voltage can achieve a large output power.