firing angle control for an SCR

int pi=30;
int po=26;

void setup() {

Serial.begin(9600);
pinMode(pi,INPUT);
pinMode(po,OUTPUT);
}

void loop() {
int m=digitalRead(pi);
if(m==HIGH)
{

delay(5);
digitalWrite(po,HIGH);
Serial.println("5V");
delay(2);
digitalWrite(po,LOW);
}
else
{
digitalWrite(po,LOW);
Serial.println("0V");
delay(500);
}}