int transistorLine = 0;
int voltageSens = 3;
boolean dynamoOn= false;

byte testruns = 15;
int thres = 680;


void setup() {                .
  pinMode(transistorLine, OUTPUT);  
  pinMode(voltageSens, INPUT);
}

void loop() {
  if (dynamoOn = IsDynamoRunning() ) digitalWrite(transistorLine, LOW);
  else digitalWrite(transistorLine, HIGH);
}

boolean IsDynamoRunning() {
  byte test= 0;
  for (byte i = 0; i < testruns; i++ ) {
   if (analogRead(voltageSens) >= thres ) test++;
   delay(1); 
  }
  if (test == testruns) {
    return true;
  }
  else if (test == 0){
    return false;
  }
  else return dynamoOn;
}