// measure frequency of the in or out pin in reference to ground
// bridge the in and out pin using a jumper to allow for the transfer of information

const int in = 0;
const int out = 1;

void setup() {
  pinMode(in, INPUT);
  pinMode(out, OUTPUT); 
  digitalWrite(out, LOW);
}

void loop() {
  digitalWrite(out, 1 - digitalRead(in));
}