Light a eCandle
Against the darkness of all dangers, fears and sadness, keep a eCandle light.
eCandle
Take a piece a paper, a resistor, a LED, the following lines of code and light a eCandle. This may be a ePrayer for the victims of the vicious terrorist attacks in Paris.
/* Constants */
const int16_t _maxDutyCycle = 256;
/* Custom variables */
volatile uint8_t *_outputPort = &PORTB;
uint8_t _outputPin = PINB5;
int16_t _absMax = (_maxDutyCycle / 1);
int16_t _absMin = (_maxDutyCycle / 4);
uint16_t _interval = 2;
/* Application variables */
volatile uint8_t _pwmOutputPinMask = (1 << _outputPin);
uint8_t _defTCCR2B;
int16_t _min = _absMin;
int16_t _max = _absMax;
void setup(void)
{
/* Initialize PWM */
InitializePWM();
/* Set default values */
}
/* Fliker LED attached to the output pin */
void loop(void)
{
_max = random(_min, _absMax);
for (int16_t i = _min; i <= _max; i++) {
DutyCycle(i);
delay(_interval);
}
_min = random(_absMin, _max);
for (int16_t i = _max; i >= _min; i--) {
DutyCycle(i);
delay(_interval);
}
}
/* Set up output pin and timer2, clockRate at 5 */
void InitializePWM(void)
{
cli();
/* Set data direction */
*(_outputPort - 1) |= _pwmOutputPinMask;
/* Set timer 2, Mode 3, aka Fast PWM mode */
TCCR2A = (1 << WGM20) | (1 << WGM21);
/* Set timer 2 prescaler */
TCCR2B = 0x05;
/* Record default value */
_defTCCR2B = TCCR2B;
/* Output Compare Match A Interrupt Enable and Overflow Interrupt Enable */
TIMSK2 = (1 << OCIE2A) | (1 << TOIE2);
sei();
}
void DutyCycle(int16_t dutyCycle)
{
if (dutyCycle <= 0) {
dutyCycle = 0;
/* Stop clock */
TCCR2B = 0x00;
/* Set output pin to low state */
*(_outputPort) &= ~_pwmOutputPinMask;
} else if (dutyCycle >= _maxDutyCycle) {
dutyCycle = _maxDutyCycle;
/* Stop clock */
TCCR2B = 0x00;
/* Set output pin to high state */
*(_outputPort) |= _pwmOutputPinMask;
} else {
/* Set trigger level for next compare cycle */
OCR2A = dutyCycle;
/* resume clock */
TCCR2B = _defTCCR2B;
}
}
/* Invoked after TCNT2 overflows */
ISR(TIMER2_OVF_vect)
{
/* Set output pin to high state */
*(_outputPort) |= _pwmOutputPinMask;
}
/* Invoked after TCNT2 equals COMPA */
ISR(TIMER2_COMPA_vect)
{
/* Set output pin to low state */
*(_outputPort) &= ~_pwmOutputPinMask;
}
You may customize your own candle using the custom variables: _outputPort for any port,
_outputPin for any pin from this port, _absMax absolute max intensity, _absMin absolute min intensity and flickering intervals in milliseconds.