I'm using a 6ms pulse to power two IR LED's using 1 ohm resistors at 5VDC. The circuit is drawing about 140 ma average based on my power supply current reading.
The 6ms pulses are applied with two timers, timer 0 is a 100 ms timer and timer 1 is the 6ms timer so On time is 6ms and off time is 100ms
As I was testing, I made a programming error where the pulse stayed on drawing 400 ma current for a few seconds.
What kind of protection can I use to solve a potential AVR malfunction or mosfet malfunction or development software error that would protect those led's from burning up?
I am familiar with PTC fuses but is there any other method using capacitors or something?
Code so far
#include <tiny45.h>
volatile unsigned char WheelTenMSTimer = 10; // Decrements once per Millisecond resets to 10 when WheelPin state is read.
volatile unsigned char WheelState = 2; // 2 = Unknown State initially
volatile unsigned char PreviousWheelState = 2; // 2= Unknown State initially Valid 1 = High, 0 = Low
volatile unsigned char IRLedOutputFlag = 0;
volatile unsigned char RollerSenseCount = 50; // Valid 0 = Sensor Low, 100 = Sensor High
volatile unsigned char WheelPulseCounter = 0;
// alarm
#define AlarmPin PINB4
#define AlarmPort PORTB
#define AlarmDDR DDRB
#define AlarmOn AlarmPort |=(1 <<AlarmPin)
#define AlarmOff AlarmPort &=~(1 << AlarmPin)
// RollerSensor INPUT
#define WheelPin PINB1
#define WheelPort PORTB
#define WheelDDR DDRB
#define WheelPinHigh ( (PINB & (1 << WheelPin)) == (1 << WheelPin) )
// Roller sensor IR Led OUTPUT
#define RollerPin PINB3
#define RollerPinPort PORTB
#define RollerPinDDR DDRB
#define RollerPinOn RollerPinPort |=(1 << RollerPin)
#define RollerPinOff RollerPinPort &=~(1 << RollerPin)
//ScreenFrame Sensor INPUT
#define FrameInputSensorPin PINB0
#define FrameInputSensorPort PORTB
#define FrameInputSensorDDR DDRB
#define FrameInputSensorPinHigh ( (PINB & (1 << FrameInputSensorPin)) == (1 << FrameInputSensorPin) )
// ScreenFrame Sensor OUTPUT
#define FrameOutputSensorPin PINB2
#define FrameOutputSensorPort PORTB
#define FrameOutputSensorDDR DDRB
#define FrameOutputLedON FrameOutputSensorPort |=(1 << FrameOutputSensorPin)
#define FrameOutputLedOFF FrameOutputSensorPort &=~(1 << FrameOutputSensorPin)
interrupt [TIM0_OVF] void timer0_ovf_isr(void)
{
// 1MS interrupts
TCNT0 = 131;
if (WheelTenMSTimer > 0)
{
WheelTenMSTimer--; // Decrement 10 ms timer
}
}
interrupt [TIM1_COMPA] void timer1_compa_isr(void)
{
// compare OCR1A = 200 // Clock /256
// 6.4MS timer interrupt
if (WheelTenMSTimer == 0) //Turn the IR Led Flags on and reset ten MS timer
{
WheelTenMSTimer = 100; // 100 MS until next on cycle
IRLedOutputFlag = 2; // Set to turn IRE led ON
}
if (IRLedOutputFlag == 1) // Turn off IR LED
{
FrameOutputLedOFF;
RollerPinOff;
IRLedOutputFlag = 0;
}
if (IRLedOutputFlag == 2)
{
FrameOutputLedON;
RollerPinOn;
IRLedOutputFlag = 1; // Set so next time this interrupts 6.4MS turn off IR LED
}
}
void TestValidWheelPulse();
void TestAlarmConditions();
void main(void)
{
// Setup timers
TCCR0A=(0<<COM0A1) | (0<<COM0A0) | (0<<COM0B1) | (0<<COM0B0) | (0<<WGM01) | (0<<WGM00);
TCCR0B=(0<<WGM02) | (0<<CS02) | (1<<CS01) | (1<<CS00);
TCNT0=0x00;
OCR0A=0x00;
OCR0B=0x00;
TIMSK=(1<<OCIE1A) | (0<<OCIE1B) | (0<<OCIE0A) | (0<<OCIE0B) | (0<<TOIE1) | (1<<TOIE0);
// clock / 256
TCCR1 =(1<<CTC1)|(0<< PWM1A )| (0<<COM1A1) |(0<< COM1A0) |(1<<CS13) |(0<<CS12) |(0<<CS11) |(1<<CS10);
OCR1A = 200;
OCR1C = 200;
WheelDDR &=~(1 << WheelPin); // Input
WheelPort |= (1 << WheelPin); // Pull up
FrameInputSensorDDR &=~(1 <<FrameInputSensorPin); // Input
FrameInputSensorPort |= (1 <<FrameInputSensorPin); // Pull up
AlarmDDR |=(1 << AlarmPin);
RollerPinDDR |=(1 << RollerPin);
FrameOutputSensorDDR |=(1 << FrameOutputSensorPin);
#asm("sei") // Turn on interrupts
while (1)
{
while (IRLedOutputFlag == 1) // When Timer1 Interrupt turns IR LED on Read status IR Receiver until IR Led turns off
{
if (!FrameInputSensorPinHigh) // Reset all counters if no frame in sensor beam
{
AlarmOff;
WheelState = 2; // 2 = Unknown State initially
PreviousWheelState = 2; // 2= Unknown State initially Valid 1 = High, 0 = Low
RollerSenseCount = 50; // Valid 0 = Sensor Low, 100 = Sensor High
WheelPulseCounter = 0; // Flag for alarm when counts up to 16 , ten inches have passed
}
if (WheelPinHigh)
{
if (RollerSenseCount < 100)
{
RollerSenseCount++; // Increase counter if IR sensor is receiving
}
}
else // WheelPin is LOW
{
if (RollerSenseCount > 0)
{
RollerSenseCount--; // Decrease counter if IR sensor is not receiving
}
}
}
if (IRLedOutputFlag == 0) // When Timer1 interrupt turns IR led off Reset the counter
{
if (RollerSenseCount == 100) // Test if Roller Sensor valid Receive
{
RollerSenseCount = 50; // Reset to neutral
WheelState = 1;
}
else
{
if (RollerSenseCount == 0) // Test if Roller Sensor valid Receive
{
RollerSenseCount = 50; // Reset to neutral
WheelState = 0;
}
}
}
if (WheelState != 2)
{
TestValidWheelPulse();
TestAlarmConditions();
}
}
}
void TestValidWheelPulse()
{
if (PreviousWheelState == 2)
{
PreviousWheelState = WheelState;
}
if( WheelState == 0)
{
if (PreviousWheelState == 1) // Record a valid pulse
{
WheelPulseCounter++;
PreviousWheelState = WheelState;
WheelState = 2;
}
}
else // WheelState = 1
{
if (PreviousWheelState == 0) // Record a valid pulse
{
WheelPulseCounter++;
PreviousWheelState = WheelState;
WheelState = 2;
}
}
}
void TestAlarmConditions()
{
if (WheelPulseCounter == 2)
{
AlarmOn;
}
}
