diff --git a/uc/Makefile b/uc/Makefile
index fb2d8ae..d6f2d35 100755
--- a/uc/Makefile
+++ b/uc/Makefile
@@ -81,19 +81,20 @@ AVRDUDE_PROGRAMMER	= usbtiny
 MCU	= atmega48
 F_CPU	= 1000000
 #
-# Predefine the TYPE and SENSORx C macros in main.h via this Makefile. Override the
-# defaults on the command line by typing:
+# Predefine the TYPE and SENSORx C macros in main.h via this Makefile.
+# Override the defaults on the command line by typing:
 # make TYPE=xxxx SENSOR0=yyyy ...
 #
-TYPE = 2301
-METERCONST = 7091
+DBG = 0
+#
+TYPE = 2300501
 #
 SENSOR0 = 0123456789abcdef0123456789abcde0
 SENSOR1 = 0123456789abcdef0123456789abcde1
 SENSOR2 = 0123456789abcdef0123456789abcde2
 SENSOR3 = 0123456789abcdef0123456789abcde3
 #
-CEXTRA = -D TYPE=$(TYPE) -D METERCONST=$(METERCONST) -D POWERCONST=$(POWERCONST) -D 'SENSOR0="$(SENSOR0)"' -D 'SENSOR1="$(SENSOR1)"' -D 'SENSOR2="$(SENSOR2)"' -D 'SENSOR3="$(SENSOR3)"'
+CEXTRA = -D DBG=$(DBG) -D TYPE=$(TYPE) -D 'SENSOR0="$(SENSOR0)"' -D 'SENSOR1="$(SENSOR1)"' -D 'SENSOR2="$(SENSOR2)"' -D 'SENSOR3="$(SENSOR3)"'
 #####################################################################################
 
 #####################################################################################
diff --git a/uc/main.c b/uc/main.c
index 6d28722..a7d6019 100644
--- a/uc/main.c
+++ b/uc/main.c
@@ -73,43 +73,49 @@ ISR(PCINT2_vect) {
 **/
 
 // interrupt service routine for ADC
-ISR(TIMER2_OVF_vect) {
+ISR(TIMER2_COMPA_vect) {
+#if DBG > 0
+  PORTD |= (1<<PD4);
+#endif
   // read ADC result
   // add to nano(Wh) counter
-  if (muxn < 2) {
-    MacU16X16to32(aux[muxn].nano, METERCONST, ADC);
+  MacU16X16to32(aux[muxn].nano, METERCONST, ADC);
 
-    if (aux[muxn].nano > WATT) {
-       measurements[muxn].value++;
-       aux[muxn].pulse = true;
-       aux[muxn].nano -= WATT;
-       aux[muxn].pulse_count++;
-    }
-
-    if (timer == SECOND) {
-      aux[muxn].nano_start = aux[muxn].nano_end;
-      aux[muxn].nano_end = aux[muxn].nano;
-      aux[muxn].pulse_count_final = aux[muxn].pulse_count;
-      aux[muxn].pulse_count = 0;
-      aux[muxn].power = true;
-    }
+  if (aux[muxn].nano > WATT) {
+     measurements[muxn].value++;
+     aux[muxn].pulse = true;
+     aux[muxn].nano -= WATT;
+     aux[muxn].pulse_count++;
   }
 
-  // rotate the available ADC input channels (0 to 7)
+  if (timer == SECOND) {
+    aux[muxn].nano_start = aux[muxn].nano_end;
+    aux[muxn].nano_end = aux[muxn].nano;
+    aux[muxn].pulse_count_final = aux[muxn].pulse_count;
+    aux[muxn].pulse_count = 0;
+    aux[muxn].power = true;
+  }
+
+  // cycle through the available ADC input channels (0 and 1)
   muxn++;
-  if (!(muxn &= 0x7)) timer++;
+  if (!(muxn &= 0x1)) timer++;
   if (timer > SECOND) timer = 0;
 
-  // but only use ADC0 and 1
-  if (muxn < 2) {
-    ADMUX &= 0xF8;
-    ADMUX |= muxn;
-  
-    // start a new ADC conversion
-    ADCSRA |= (1<<ADSC);
-  }
-}
+  ADMUX &= 0xF8;
+  ADMUX |= muxn;
+  // start a new ADC conversion
+  ADCSRA |= (1<<ADSC);
 
+#if DBG > 0
+  PORTD &= ~(1<<PD4);
+#endif
+
+#if DBG > 1
+  aux[muxn].nano = WATT+1;
+  timer = SECOND;
+#endif
+}
+ 
 // interrupt service routine for analog comparator
 ISR(ANALOG_COMP_vect) {
   uint8_t i;
@@ -197,7 +203,10 @@ void setup()
   // enable INT0 and INT1 interrupts
   EIMSK = (1<<INT0) | (1<<INT1);
 
-
+#if DBG > 0
+  // re-use PD4 pin for tracing interrupt times
+  DDRD |= (1<<DDD4);
+#else
   // PD4=PCINT20 configuration
   // set as input pin with 20k pull-up enabled
   PORTD |= (1<<PD4);
@@ -205,6 +214,7 @@ void setup()
   PCMSK2 |= (1<<PCINT20);
   //pin change interrupt enable 2
   PCICR |= (1<<PCIE2);
+#endif
 
   // analog comparator setup for brown-out detection
   // PD7=AIN1 configured by default as input to obtain high impedance
@@ -216,10 +226,20 @@ void setup()
   // bandgap select | AC interrupt enable | AC interrupt on rising edge (DS p.243)
   ACSR |= (1<<ACBG) | (1<<ACIE) | (1<<ACIS1) | (1<<ACIS0);
 
-  // Timer2 normal operation
-  // Timer2 clock prescaler set to 1 => fTOV2 = 1000kHz / 256 / 1 = 3906.24Hz (DS p.158)
-  TCCR2B |= (1<<CS20);
-  TIMSK2 |= (1<<TOIE2);
+  // Timer2 set to CTC mode (DS p.146, 154, 157)
+  TCCR2A |= 1<<WGM21;
+#if DBG > 0
+  // Toogle pin OC2A=PB3 on compare match
+  TCCR2A |= 1<<COM2A0;
+#endif
+  // Set PB3 as output pin
+  DDRB |= (1<<DDB3);
+  // Timer2 clock prescaler set to 8 => fTOV2 = 1000kHz / 256 / 8 = 488.28Hz (DS p.158)
+  TCCR2B |= (1<<CS21);
+  // Enable output compare match interrupt for timer2 (DS p.159)
+  TIMSK2 |= (1<<OCIE2A);
+  // Increase sampling frequency to 1250Hz (= 625Hz per channel)
+  OCR2A = 0x63;
 
   // disable digital input cicuitry on ADCx pins to reduce leakage current
   DIDR0 |= (1<<ADC5D) | (1<<ADC4D) | (1<<ADC3D) | (1<<ADC2D) | (1<<ADC1D) | (1<<ADC0D);
diff --git a/uc/main.h b/uc/main.h
index 5ccb93f..c5ce548 100644
--- a/uc/main.h
+++ b/uc/main.h
@@ -24,7 +24,7 @@
 # define POWER 1
 
 # define WATT 1000000000
-# define SECOND 487 // rounded down from 488.28125 - 1
+# define SECOND 624 // 625Hz - 1
 
 #ifndef SENSOR0 
   #define SENSOR0 "0123456789abcdef0123456789abcde0"
@@ -43,33 +43,33 @@
 #endif
 
 #ifndef TYPE
-  #define TYPE 2301
+  #define TYPE 2300501
 #endif
 
-#ifndef METERCONST
-  #if TYPE == 2201   // 220V - 1-phase @ 488.28Hz sampling rate
-    #define METERCONST 6783
-    #warning "220V - 1-phase selected. METERCONST set to 6783"
+#ifndef METERCONST // @ 625Hz sampling rate
+  #if TYPE == 2200501
+    #define METERCONST 5299
+    #warning "220V - 50A - 1-phase selected. METERCONST set to 5299"
 
-  #elif TYPE == 2203 // 220V - 3-phase @ 488.28Hz sampling rate
-    #define METERCONST 6721
-    #warning "220V - 3-phase selected. METERCONST set to 6721"
+  #elif TYPE == 2200503
+    #define METERCONST 5251
+    #warning "220V - 50A - 3-phase selected. METERCONST set to 5251"
 
-  #elif TYPE == 2301 // 230V - 1-phase @ 488.28Hz sampling rate
-    #define METERCONST 7091
-    #warning "230V - 1-phase selected. METERCONST set to 7091"
+  #elif TYPE == 2300501
+    #define METERCONST 5540
+    #warning "230V - 50A - 1-phase selected. METERCONST set to 5540"
 
-  #elif TYPE == 2303 // 230V - 3-phase @ 488.28Hz sampling rate
-    #define METERCONST 7026
-    #warning "230V - 3-phase selected. METERCONST set to 7026"
+  #elif TYPE == 2300503
+    #define METERCONST 5489
+    #warning "230V - 50A - 3-phase selected. METERCONST set to 5489"
 
-  #elif TYPE == 2401 // 240V - 1-phase @ 488.28Hz sampling rate
-    #define METERCONST 7399
-    #warning "240V - 1-phase selected. METERCONST set to 7399"
+  #elif TYPE == 2400501
+    #define METERCONST 5780
+    #warning "240V - 50A - 1-phase selected. METERCONST set to 5780"
 
-  #elif TYPE == 2403 // 240V - 3-phase @ 488.28Hz sampling rate
-    #define METERCONST 7331
-    #warning "240V - 3-phase selected. METERCONST set to 7331"
+  #elif TYPE == 2400503
+    #define METERCONST 5727
+    #warning "240V - 50A - 3-phase selected. METERCONST set to 5727"
   #endif
 #endif