long result;   //variable for the result of the tx_rx measurement.
int analog_pin = 39;
int tx_pin = 16;
int pin = 25;
//freqs that work: 839, 334, 555, 760
int freq = 555;
int channel = 1;

void setup() {
pinMode(tx_pin,OUTPUT);      //Pin 4 provides the voltage step
Serial.begin(115200);
digitalWrite(17,HIGH);

//pinMode(pin, OUTPUT);
ledcSetup(channel, freq, 8); // setup beeper
ledcAttachPin(pin, channel); // attach beeper

}


long tx_rx(){         //Function to execute rx_tx algorithm and return a value
                      //that depends on coupling of two electrodes.
                      //Value returned is a long integer.
  int read_high;
  int read_low;
  int diff;
  long int sum;
  int N_samples = 100;    //Number of samples to take.  Larger number slows it down, but reduces scatter.

  sum = 0;

  for (int i = 0; i < N_samples; i++){
   digitalWrite(tx_pin,HIGH);              //Step the voltage high on conductor 1.
   read_high = analogRead(analog_pin);        //Measure response of conductor 2.
   delayMicroseconds(100);            //Delay to reach steady state.
   digitalWrite(tx_pin,LOW);               //Step the voltage to zero on conductor 1.
   read_low = analogRead(analog_pin);         //Measure response of conductor 2.
   diff = read_high - read_low;       //desired answer is the difference between high and low.
 sum += diff;                       //Sums up N_samples of these measurements.
 }
  return sum;
}                         //End of tx_rx function.


void loop() {

result = tx_rx();
Serial.println(result);
//delay(100);

if(result>40000){
  ledcWrite(channel, 128); // play tone
  Serial.println("played tone");
}
else{
  ledcWriteTone(channel,0);
  Serial.println("didn't play tone");
}

}