~~META:description abstract=Fan driver for the PWM amplifier~~

Fan driver for the PWM amplifier

Max ADC input voltage is 1.1V (higher means saturated).

Output of TMP36 in volts is , targeted temperature range is at least [20 .. 100]°C, that is [0.7 .. 1.5] V.

Theorical response is 0% up to 50°C, from 0% to 100% between 50°C and 75°C and 100% above 75°C.

Needed multiplier before ADC is at most , R1=33k and R2=82k fits (0.731).

(min 0, max 1).

Using (fits an int 16) gives an average of 3.6% deviation from theorical response.

Calculation file

schematic.svg

main.c

// CPU frequency 9.6MHz
// Temperature sensor (TMP36) on ADC3 (PB3)
// MosFet output on OC0A (PB0)
 
int main(void) {
	int16_t t;
 
	ADMUX = 0x43;	// internal reference, right adjust, ADC3
	ADCSRA = 0x87;	// ADC enable, prescaler to 128 (175us/conv.)
 
	TCCR0A = 0x83;	// fast pwm on OC0A
	TCCR0B = 0x01;	// prescaler to 1 => f=37.5kHz
 
	while(1) {
		ADCSRA |= 0x40;			// start conversion
		while(ADCSRA & 0x40);		// wait for completion
 
		t = ADC - 665;
		t *= 49;			// approx.
		t /= 32;			// 1.6451
 
		if(t < 0) t = 0;		// limits
		if(t > 255) t = 255;		//
 
		OCR0A = t;
	}
 
	return 0;
}

analog