Ajuste de frecuencia con zumbador

1int buzzerPin = 8;
2int btnOn = 7;
3int btnOff = 6;
4int btnIncrease = 5;
5int btnDecrease = 4;
6int frequency = 300;
7int state = 0;
8
9void setup() {
10  pinMode(btnOn, INPUT);
11  pinMode(btnOff, INPUT);
12  pinMode(btnIncrease, INPUT);
13  pinMode(btnDecrease, INPUT);
14}
15
16void loop() {  
17  if (digitalRead(btnOn)) {
18    state = 1;
19  }
20  
21  if (digitalRead(btnOff)) {
22    state = 0;
23  }
24  
25  if (digitalRead(btnIncrease)) {
26    frequency = frequency + 50;
27    delay(100);
28  }
29  
30  if (digitalRead(btnDecrease)) {
31    frequency = frequency - 50;
32    delay(100);
33  }
34  
35  if (state == 1) {
36    tone(buzzerPin, frequency);
37  } else {
38    noTone(buzzerPin);
39  }
40}