// Program to output a square wave
// at pin D8 (LED)
// Purpose: to capture & observe the waveform
//  on an oscilloscope
//
#define led D8  // LED at D8

void setup() {
  // put your setup code here, to run once:
  pinMode(led, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:
  digitalWrite(led, HIGH);
  delay(50);  // 50ms delay, giving freq of 10Hz
  digitalWrite(led, LOW);
  delay(50);
}