How To Make DIY Arduino 30 Seconds Washing Timer, STOP COVID

1#include <TM1637Display.h>
2#define trig_pin 11
3#define echo_pin  10
4#define CLK 6
5#define DIO 7
6#define buzzer 8
7long duration;
8float  cm;
9const uint8_t Clear[] = {0, 0, 0, 0};
10
11TM1637Display display(CLK, DIO);
12void  setup(){ 
13  
14  pinMode(trig_pin, OUTPUT); 
15  pinMode(echo_pin, INPUT);  
16  pinMode(buzzer,OUTPUT); 
17  display.setBrightness(4);
18  display.setSegments(Clear);
19
20
21}
22void  countdown() {
23  for(int i=29; i>=0; i--) {
24    display.showNumberDec(i, true,  2, 2);
25    delay(1000);
26  }
27}
28
29void loop() {
30    digitalWrite(trig_pin,  LOW);
31    delayMicroseconds(2);
32    digitalWrite(trig_pin, HIGH);
33    delayMicroseconds(10);
34    duration = pulseIn(echo_pin, HIGH);
35    cm = duration * 0.034 /2;
36  if  (cm < 8 && cm >= 1) {
37      tone(8,800,40);
38      countdown();
39      tone(8,800,40);
40      display.setSegments(Clear);
41  }
42}