Arduino test: voltmeter

First experiment with Arduino. Trying to implement a voltmeter.

Each analog input of Arduino has 1024 steps. From 0 to 5 volt. This experiment used a simple voltage divider to measure roughly 0 to 12 volt (using 50k as R1 and 4k3 as R2).

By varying the values of R1 and R2, the precision and range of the measurement can be changed.

Here is the Arduino code:

// variables for input pin and control LED
  int analogInput = 1;
  int LEDpin = 13;
  int prev = LOW;
  int refresh = 1000;
  float vout = 0.0;
  float vin = 0.0;
  float R1 = 50000.0;    // !! resistance of R1 !!
  float R2 = 4300.0;     // !! resistance of R2 !!

// variable to store the value
  int value = 0;


void setup(){

  // declaration of pin modes
  pinMode(analogInput, INPUT);
  pinMode(LEDpin, OUTPUT);

  // begin sending over serial port
  Serial.begin(9600);
}

void loop(){
  // read the value on analog input
  value = analogRead(analogInput);
  //Serial.print("value=");
  //Serial.println(value);

  if (value >= 1023) {
    Serial.println("MAX!!");
    delay(refresh);
    return;
  }
  else if (value <= 0) {
    Serial.println("MIN!!");
    delay(refresh);
    return;
  }

  // blink the LED
  if (prev == LOW) {
    prev = HIGH;
  } else {
    prev = LOW;
  }
  digitalWrite(LEDpin, prev);

  // print result over the serial port
  vout = (value * 5.0) / 1024.0;
  vin = vout / (R2/(R1+R2));

  //Serial.print("vout=");
  //Serial.println(vout);

  Serial.print(vin);
  Serial.println(" volt");

  // sleep...
  delay(refresh);
}