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### Topic: Zero crossing of the Square wave (Read 1 time)previous topic - next topic

#### irfanatul

##### Mar 27, 2013, 05:24 am
hi...
i am using arduino due. i want to check the zero crossing of the AC waveform because i want to trigger six pulse thyristor. so i need zero crossing of the AC voltage.For that, i prepared a schmitt trigger which detects the zero crossing of the AC signal which gives me square wave then i put one diode so negative pulse is discard.so i am getting only positive square pulse.this pulse have maximum value is 3.0 volt.i am giving this pulse to analog pin A0.and i have written following code.

int pin2=2,pin3=3,pin4=4,pin5=5,pin6=6,pin7=7;
int sensor=A0;
void setup() {
Serial.begin(115200);
pinMode(pin2,OUTPUT);
pinMode(pin3,OUTPUT);
pinMode(pin4,OUTPUT);
pinMode(pin5,OUTPUT);
pinMode(pin6,OUTPUT);
pinMode(pin7,OUTPUT);
// put your setup code here, to run once:

}
void loop() {

int i,c;
int d[15];
for(i=1;i<=15;i++)
{
Serial.println(d);
d[0]= 1023;
c=d-d[i-1];
Serial.println(c);
if (c>0)
{
goto IRFAN;
}

}
// put your main code here, to run repeatedly:
IRFAN:
while(1)
{
//Serial.println('c');
digitalWrite(pin7,LOW);
digitalWrite(pin2,HIGH);
delayMicroseconds(3333);
digitalWrite(pin2,LOW);
digitalWrite(pin3,HIGH);
delayMicroseconds(3333);
digitalWrite(pin3,LOW);
digitalWrite(pin4,HIGH);
delayMicroseconds(3333);
digitalWrite(pin4,LOW);
digitalWrite(pin5,HIGH);
delayMicroseconds(3333);
digitalWrite(pin5,LOW);
digitalWrite(pin6,HIGH);
delayMicroseconds(3333);
digitalWrite(pin6,LOW);
digitalWrite(pin7,HIGH);
delayMicroseconds(3333);
}
}
i am taking difference of two values d and d[i-1] so i can trigger all thyristor very accurately.but when i am uploading this program, DSO is not showing me exact zero cross. i am not getting pulse at exact zero cross it is slowly moving with respect to AC waveform.so please suggest me what can i do?

#### retrolefty

#1
##### Mar 27, 2013, 05:30 amLast Edit: Mar 27, 2013, 05:48 am by retrolefty Reason: 1
Why are you reading the the signal as a analog voltage with a analogRead() statement?

The information from your schmitt trigger device is a digital timing signal and you should be reading it as a digital signal with a digitalRead() statement or using the signal to generate an interrupt.

Lefty

#### irfanatul

#2
##### Mar 27, 2013, 07:08 am
Thanks...
i will try with digitalread() command.

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