Designing a pitch-tone alarm sound circuit based on 556 integrated chip design

In 556, TH high-level trigger terminal: When the TH terminal level is greater than 2/3VCC, the output terminal OUT is low. The DIS terminal is turned on. TR low trigger: When the TR level is less than 1/3VCC. The OUT terminal presents a high level. The DIS terminal is turned off. R reset terminal: =0, OUT output low level. The DIS terminal is turned on. VC control voltage terminal: VC connected to different voltage values ​​can change the trigger level value of TH. DIS Discharge End: Turns it on or off to provide a path for discharging or charging the RC loop. OUT output.