const int OhmMeter = 0; 
const int R3 = 6; 
const int R2 = 5; 
const int R1 = 4; 
float R = 0.00; 
void calculate_resistor() { 
  float v_ref = 4.94; 
  float r1 = 0.00; 
  float r_ref1 = 1000.00; 
  float adc_value1 = 0.00;
  float voltage1 = 0.00; 
  float r2 = 0.00; 
  float r_ref2 = 10000.00;
  float adc_value2 = 0.00;
  float voltage2 = 0.00; 
  float r3 = 0.00; 
  float r_ref3 = 100000.00; 
  float adc_value3 = 0.00;
  float voltage3 = 0.00; 
  pinMode(R1, OUTPUT); 
  pinMode(R2, INPUT); 
  pinMode(R3, INPUT); 
  digitalWrite(R1, HIGH); 
  for (int i = 0; i < 20 ; i++) 
  { 
    adc_value1 = adc_value1 + analogRead(OhmMeter); 
    delay(3); 
  } 

  adc_value1 = adc_value1 / 20; 

  if (adc_value1 < 1022.90) 
  { 
    voltage1 = ((adc_value1 * v_ref) / 1024); 
    r1 = (voltage1 * r_ref1) / (v_ref - voltage1); 
  } 
  pinMode(R1, INPUT); 
  pinMode(R2, OUTPUT); 
  pinMode(R3, INPUT); 
  digitalWrite(R2, HIGH); 
  for (int i = 0; i < 20 ; i++) 
  { 
    adc_value2 = adc_value2 + analogRead(OhmMeter); 
    delay(3); 
  } 
  adc_value2 = adc_value2 / 20; 
  if (adc_value2 < 1022.90) 
  { 
    voltage2 = ((adc_value2 * v_ref) / 1024); 

    r2 = (voltage2 * r_ref2) / (v_ref - voltage2); 
  } 
  pinMode(R1, INPUT); 
  pinMode(R2, INPUT); 
  pinMode(R3, OUTPUT); 
  digitalWrite(R3, HIGH); 
  for (int i = 0; i < 20 ; i++) 
  { 
    adc_value3 = adc_value3 + analogRead(OhmMeter); 
    delay(3); 
  } 
  adc_value3 = adc_value3 / 20; 
  if (adc_value3 < 1022.90) 
  { 
    voltage3 = ((adc_value3 * v_ref) / 1024); 
    r3 = (voltage3 * r_ref3) / (v_ref - voltage2); 
  } 
  r1 = r1 / 1000; 

  r2 = r2 / 1000; 

  r3 = r3 / 1000; 
  if (r1 < 2 && r2 < 101 && r3 < 1001) R = r1*1000; 
  else if (r1 > 2 && r2 < 101 && r3 < 1001) R = r2; 
  else if (r1 > 2 && r2 > 101 && r3 < 2000) R = r3; 
  else R = 0.00; 
  Serial.print("R = "); 

  Serial.println(R, 2); 
} 
void setup() { 

  Serial.begin(9600); 
} 
void loop() { 
  calculate_resistor(); 
  Serial.println("_________________________________________"); 

  delay(2500); 
}