diff --git a/firmware/main.c b/firmware/main.c
index 38ea013..e1d4df8 100644
--- a/firmware/main.c
+++ b/firmware/main.c
@@ -30,7 +30,7 @@
 #include "main.h" // main definitions
 
 /* variables */
-volatile uint8_t stateD; // the state of port D
+volatile uint8_t state_portD; // the state of port D
 
 /* switch off LED */
 void led_off(void)
@@ -51,30 +51,30 @@ void led_toggle(void)
 }
 
 /* scale on interrupt
-   PCI2 Interrupt Vector for PCINT[23:16]/PORTD
-*/
+ * PCI2 Interrupt Vector for PCINT[23:16]/PORTD
+ */
 ISR(PCINT2_vect)
 {
-	if ((stateD&(1<<SCALE_ON))!=(PIND&(1<<SCALE_ON))) { // scale on state changed
+	if ((state_portD&(1<<SCALE_ON))!=(PIND&(1<<SCALE_ON))) { // scale on state changed
 		if (PIND&(1<<SCALE_ON)) {
 			led_on();
 		} else {
 			led_off();
 		}
 	}
-	stateD = PIND; // save new state
+	state_portD = PIND; // save new state
 }
 
-/* timer 1 OCR1A match interrupt
- * use it to toogle LED
+/* PWM weight signal
+ * analog comparator interrupt
  */
-ISR(TIMER1_COMPA_vect)
+ISR(ANALOG_COMP_vect)
 {
-/*
-	if (blink_flag) {
-		led_toggle();
+	if (ACSR&(1<<ACO)) { // PWM high
+		led_on();
+	} else { // PWM low
+		led_off();
 	}
-*/
 }
 
 /* disable watchdog when booting */
@@ -99,14 +99,25 @@ void io_init(void)
 	/* LED */
 	DDRB |= (1<<LED); // LED is driven by pin (set as output)
 	led_off();
+
 	/* scale on signal */
 	DDRD &= ~(1<<SCALE_ON); // SIGNAL_ON is input (should be per default)
 	PCIFR &= ~(1<<PCIF2); // clear interrupt flag for SCALE_ON on PCINT[23:16]/PORTD
 	PCICR |= (1<<PCIE2); // enable interrupt for PCINT[23:16]/PORTD
 	PCMSK2 |= (1<<PCINT21); // enable interrupt for SCALE_ON
-	stateD = PIND; // save state to detect changes
+	state_portD = PIND; // save state to detect change
+
 	/* PWM scale weight signal on analog comparator */
-	DDRD &= ~((1<<SCALE_PWM)||(1<<REF_PWM)); // analog comparator is input (should be per default)
+	DDRD &= ~((1<<SCALE_PWM)|(1<<REF_PWM)); // analog comparator is input (should be per default)
+	ADCSRA &= ~(1<<ADEN); // switch off ADC
+	ADCSRB &= ~(1<<ACME); // disable analog comparator multiplexer, use AIN1 as negative input (should be per default)
+	ACSR &= ~(1<<ACD); // enable analog comparator (should be per default)
+	ACSR &= ~(1<<ACBG); // use AIN0 as positiv input (should be per default)
+	ACSR |= (1<<ACI); // clear analog comparator interrup flag
+	ACSR |= (1<<ACIC); // enable analog comparator input capture (on timer 1)
+	ACSR &= ~((1<<ACIS1)|(1<<ACIS0)); // comparator interrupt on output toggle
+	DIDR1 |= ((1<<AIN1D)|(1<<AIN0D)); // disable digital input buffer on AIN0 and AIN1
+	ACSR |= (1<<ACIE); // enable analog comparator interrupt
 
 	sei(); /* enable interrupts */
 }
diff --git a/firmware/main.h b/firmware/main.h
index 7e5f734..31251d9 100644
--- a/firmware/main.h
+++ b/firmware/main.h
@@ -25,15 +25,16 @@
  */
 #define SCALE_ON PD5
 /* PWM weight signal
- * high time defines the weight (propotionnally)
- * low time is constant
- * signal level is 500mV
+ * PWM frequency is ~3Hz
+ * high time increases with increasing weight (propotionnally)
+ * low time decreases with increasing weight
+ * signal level is 1V
  * positive pin of analog comparator used to measure PWM
  * pin: PD6, AIN0, D6
 */
 #define SCALE_PWM PD6
 /* negative pin of analog comparator
- * set at 100-400mV using voltage divider
+ * set at 0.2-0.8V using voltage divider
  * used to detect PWM signal change
  * pin: PD7, AIN1, D7
  */