diff --git a/DCCTimer.h b/DCCTimer.h
index ed87e1f..2567a69 100644
--- a/DCCTimer.h
+++ b/DCCTimer.h
@@ -124,6 +124,8 @@ private:
   static uint16_t usedpins;
   // cached analog values (malloc:ed to actual number of ADC channels)
   static int *analogvals;
+  // ids to scan (new way)
+  static byte *idarr;
   // friend so that we can call scan() and begin()
   friend class DCCWaveform;
   };
diff --git a/DCCTimerAVR.cpp b/DCCTimerAVR.cpp
index 5ff0e52..471ee24 100644
--- a/DCCTimerAVR.cpp
+++ b/DCCTimerAVR.cpp
@@ -120,12 +120,13 @@ void DCCTimer::reset() {
 }
 
 #if defined(ARDUINO_AVR_MEGA) || defined(ARDUINO_AVR_MEGA2560)
-#define NUM_ADC_INPUTS 15
+#define NUM_ADC_INPUTS 16
 #else
-#define NUM_ADC_INPUTS 7
+#define NUM_ADC_INPUTS 8
 #endif
 uint16_t ADCee::usedpins = 0;
 int * ADCee::analogvals = NULL;
+byte *ADCee::idarr = NULL;
 bool ADCusesHighPort = false;
 
 /*
@@ -135,16 +136,26 @@ bool ADCusesHighPort = false;
  */
 int ADCee::init(uint8_t pin) {
   uint8_t id = pin - A0;
-  if (id > NUM_ADC_INPUTS)
+  byte n;
+  if (id >= NUM_ADC_INPUTS)
     return -1023;
   if (id > 7)
     ADCusesHighPort = true;
   pinMode(pin, INPUT);
   int value = analogRead(pin);
-  if (analogvals == NULL)
-    analogvals = (int *)calloc(NUM_ADC_INPUTS+1, sizeof(int));
+  if (analogvals == NULL) {
+    analogvals = (int *)calloc(NUM_ADC_INPUTS, sizeof(int));
+    idarr = (byte *)calloc(NUM_ADC_INPUTS+1, sizeof(byte));
+    for (n=0 ; n <= NUM_ADC_INPUTS; n++)
+      idarr[n] = 255;
+  }
+  for (n=0 ; n <= NUM_ADC_INPUTS; n++) {
+    if (idarr[n] == 255) {
+      idarr[n] = id;
+      break;
+    }
+  }
   analogvals[id] = value;
-  usedpins |= (1<<id);
   return value;
 }
 int16_t ADCee::ADCmax() {
@@ -168,8 +179,7 @@ int ADCee::read(uint8_t pin, bool fromISR) {
 #pragma GCC push_options
 #pragma GCC optimize ("-O3")
 void ADCee::scan() {
-  static byte id = 0;        // id and mask are the same thing but it is faster to 
-  static uint16_t mask = 1;  // increment and shift instead to calculate mask from id
+  static byte num = 0;       // index into id array
   static bool waiting = false;
 
   if (waiting) {
@@ -181,45 +191,26 @@ void ADCee::scan() {
     low = ADCL; //must read low before high
     high = ADCH;
     bitSet(ADCSRA, ADIF);
-    analogvals[id] = (high << 8) | low;
-    // advance at least one track
-    // for scope debug TrackManager::track[1]->setBrake(0);
+    analogvals[idarr[num]] = (high << 8) | low;
     waiting = false;
-    id++;
-    mask = mask << 1;
-    if (id == NUM_ADC_INPUTS+1) {
-      id = 0;
-      mask = 1;
-    }
   }
   if (!waiting) {
-    if (usedpins == 0) // otherwise we would loop forever
-      return;
-    // look for a valid track to sample or until we are around
-    while (true) {
-      if (mask  & usedpins) {
-	// start new ADC aquire on id
+    // cycle around in-use analogue pins
+    num++;
+    if (idarr[num] == 255)
+      num = 0;
+    // start new ADC aquire on id
 #if defined(ADCSRB) && defined(MUX5)
-	if (ADCusesHighPort) { // if we ever have started to use high pins)
-	  if (id > 7)          // if we use a high ADC pin
-	    bitSet(ADCSRB, MUX5); // set MUX5 bit
-	  else
-	    bitClear(ADCSRB, MUX5);
-	}
-#endif
-	ADMUX=(1<<REFS0)|(id & 0x07); //select AVCC as reference and set MUX
-	bitSet(ADCSRA,ADSC); // start conversion
-	// for scope debug TrackManager::track[1]->setBrake(1);
-	waiting = true;
-	return;
-      }
-      id++;
-      mask = mask << 1;
-      if (id == NUM_ADC_INPUTS+1) {
-	id = 0;
-	mask = 1;
-      }
+    if (ADCusesHighPort) {     // if we ever have started to use high pins)
+      if (idarr[num] > 7)              // if we use a high ADC pin
+	bitSet(ADCSRB, MUX5);  // set MUX5 bit
+      else
+	bitClear(ADCSRB, MUX5);
     }
+#endif
+    ADMUX = (1 << REFS0) | (idarr[num] & 0x07); // select AVCC as reference and set MUX
+    bitSet(ADCSRA, ADSC);               // start conversion
+    waiting = true;
   }
 }
 #pragma GCC pop_options