# A small problem with Input Capture with ATmega16

Status
Not open for further replies.

#### johndo

##### New Member
Hello,

I've made myself a small project that simply counts up by 1 from a starting number of 0.

I'm using Input Capture from Timer 1, and generating a square wave on Timer 0 since the input capture is edge triggered.

My problem is that when I plug the battery in, it shows the LCD 'welcome screen' just fine and then it starts counting up. Like this:

Number: 000 --> Number: 001 --> Number: 002

My problem is that this is a input capture interrupt, it should not trigger at all and not count up unless there is a edge triggered signal in the ICP pin (PD6). So in other words I'm expecting the LCD to simply blink the cursor by default if there is no input at PD6. Like this:
# <-- This is the flashing cursor on an empty LCD

In Timer 0 I've created a 25 khz square wave signal that is also run under interrupt. This signal comes out of PD5 and under my expectation UNLESS this signal via a wire is connected to PD6 the LCD should not count up and remain at the cursor as shown above.

However from testing this is what I'm getting:

1) Upon connecting the battery it shows the welcome screen on the LCD and starts counting up by itself, even when there is no wire connected to PD6!

2) So I then make a wire connection from PD5 to PD6 (the ICP pin). The LCD still continues to count up.

3) I then remove the connection and the LCD stops counting. EG:

Number: 020 --> Number: 020 --> Number: 020

4) If I make a connection between PD6 and PD5 once more it then starts counting like:

Number: 021 --> Number: 022 --> Number: 023

5) And if I remove the wire connection it stops counting up and stays at the same number and etc...

I've included my code here, so can anyone please tell me where I'm going wrong because I'd like it to not count at all *unless* a signal via PD5 is sent to PD6 (ICP pin) that is carrying the edge triggered square wave.

Code:
#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>
#include "lcd.h"

#define F_CPU 12000000UL

// Define Global Variables here
int NUMBER = 0;
unsigned char i;

// Define Function Prototypes here
int welcome();
int numberLCD(int NUMBER);

int main(void)
{

// Initialize the LCD

//Clear the screen
LCDClear();

welcome(); // Welcome the user to the device

sei(); // Enable Global Interrupts

TIMSK = 0x22; // Allows input capture, enables Timer 0 COMPA interrupt
TCCR1A = 0x00;
TCCR1B = 0x41; // Enable leading edge input capture, prescaler = 1
TCCR0 = 0xA; // Enable CTC interrupts, prescaler = 8
OCR0 = 30; // 25khz pulse with duty cycle at 50% for square pulse
DDRD |= (1 << PD5); // Set bit 5 as output

while(1)
{
}

return 0;
}

ISR(TIMER1_CAPT_vect)
{
// Capture Interrupt Routine
NUMBER++;
numberLCD(NUMBER);
}

ISR(TIMER0_COMP_vect)
{
// Compare Match Interrupt Routine
PORTD ^= 0x20; // Toggle PD5

}

int welcome()
{
// Simple string printing
LCDWriteString("Welcome! ");

// Delay to show text
for(i=0;i<125;i++) _delay_loop_2(0);

// Clear the screen
LCDClear();

return 0;
}

int numberLCD(int NUMBER)
{
LCDWriteString("Number:");

// Print the current number with a field length of 3
LCDWriteIntXY(10,0,NUMBER,3);

for(i=0;i<30;i++) _delay_loop_2(0);

// LCDClear();
return 0;
}

Also by the way the signal generated at PD5 is large enough in volts as it goes through some amplification. Oh yeah and im using atmega16.

thanks everyone

Status
Not open for further replies.