How does the camera set the timer to count down?

Setting method; Take Huawei's mobile phone operation as an example:

1. First turn on the camera with its own software in the mobile phone, as shown below.

2. After turning on the camera and entering the shooting page, open the settings page to the right, as shown below.

3. After opening the camera settings page, you can see taking pictures regularly in the page, as shown below.

4. Then open the timed photo page, and select the timed seconds in the page. Under normal circumstances, 5 seconds is enough, as shown below.

5. Click to select the appropriate number of seconds, and then return to the settings page. The time when you can see the regular photos has been set, as shown below.

6. After the setting is completed, return to the shooting page and press the shutter button. You can see that the shutter button has become a countdown timer to shoot, as shown below.