Countdown timer

I need a countdown timer for about 20 to 10 seconds. The starting switch should be a push to make button. If the countdown could be set to different time is better and when it reaches 0 a sound will be heard to indicate that the time is up. If you could provide me with a good schematic since on Google I wasn’t able to find one?

If you don't need a readout like 20, 19, 18 etc on a screen this is very simple. As your timings don't seem to be required to be highly accurate, you can use a simple 555 timer. Adjusting one of the resistors will alter the time so you can have continuous control via a potentiometer. To make the sound, join it's output to an AND gate with another 555 as an astable at audio frequency (1khz?) to the other input. Connect the AND output to a piezo (probably quite quiet this way).

google for "countdown timer circuit" gives tons of hits. this one is near the top of the second page - https://www.electro-tech-online.com/threads/countdown-timer.21742/

I wish that the number will be displayed so I could know how much time there is left. Since this countdown timer will be used in a quiz.