int midPoint = 1023 / 2;
int state = 0;
int delta = 100;
int thresholdHigh = (midPoint + delta);
int thresholdLow = (midPoint - delta);

int maxPeak  = 0;
int minPeak = 1023;
int val;

const int Pot = A0;
uint32_t now;

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200);

}

void loop() {
  // put your main code here, to run repeatedly:
  static uint32_t lastObsMs = 0;
  now = millis();
  if (now - lastObsMs > 20) {
    val  = analogRead(Pot);
    switch (state) {
      case 0: // low
        if (val < minPeak) minPeak = val;
        if (val >  thresholdHigh) {
          state = 1;
          reportChange();
          updateLimits();
          maxPeak = 0;
        }
        break;
      case 1:  // high
        if (val > maxPeak) maxPeak = val;
        if (val <  thresholdLow) {
          state = 0;
          reportChange();
          updateLimits();
          minPeak = 1023;
        }
        break;
    }
    lastObsMs = now;
  }
  report();
}

void reportChange() {
  return;
  Serial.print(val); Serial.print(state == 1 ? "^" : "v");
  Serial.print("[");
  Serial.print(minPeak);
  Serial.print(",");
  Serial.print(maxPeak);
  Serial.print("] ");
  if (state == 0 )Serial.println();
}

void updateLimits() {
  long weight = 5;
  switch (state) {
    case 0: // low, so shift towards maxPeak
      midPoint = (midPoint * weight + maxPeak) / (1 + weight);
      break;
    case 1: // high, so shift towards minPeak
      midPoint = (midPoint * weight + minPeak) / (1 + weight);
      break;
  }
  thresholdHigh = midPoint + delta;
  thresholdLow = midPoint - delta;
}


void report() {
  static uint32_t last = -1000;
  char buff[80];
  if (now - last > 100) {
    last = now;
    snprintf(buff, 80, "val:%d low:%d high:%d", val, thresholdLow, thresholdHigh );
    Serial.println(buff);
  }
}