Arduino minimum high threshold?

[Sketco]

Just some quick code to verify whether the input is actually registering.

const int SWtestPin = A0;
const int LEDpin = 8;
bool PBstart = 0;


void setup() {
  pinMode (LEDpin, OUTPUT);
  pinMode (SWtestPin, INPUT);
  Serial.begin(9600);
}

void loop()
{
  digitalRead(SWtestPin);
  Serial.print(PBstart);

if(SWtestPin == true)
{
  PBstart = 1;
}
else
{
  PBstart = 0;
}
  
  digitalWrite(LEDpin, PBstart);
}