Introduction: How to Make an Arduino Ohm Meter

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We find it difficult to read color codes on resistors to find its resistance. In order to overcome the difficulty of finding the resistance value, we are going to build a simple Ohm Meter using Arduino. The basic principle behind this project is a Voltage Divider Network. The value of the unknown resistance is displayed on 16*2 LCD display.

Step 1: Components Required:-

Step 2: Circuit and Connections:-

LCD PIN 1------------GND

LCD PIN 2------------VCC

LCD PIN 3------------Middle pin of the pot

LCD PIN 4------------D12 of arduino

LCD PIN 5------------GND

LCD PIN 6------------D11 of arduino

LCD PIN 7------------NC

LCD PIN 8------------NC

LCD PIN 9------------NC

LCD PIN 10----------NC

LCD PIN 11----------D5 of arduino

LCD PIN 12----------D4 of arduino

LCD PIN 13----------D3 of arduino

LCD PIN 14----------D2 of arduino

LCD PIN 15----------VCC

LCD PIN 16----------GND

Step 3: Calculating Resistance Using Arduino Ohm Meter:

The working of this Resistance Meter is very simple and can be explained using a simple voltage divider network shown below.

From the voltage divider network of resistors R1 and R2,

Vout = Vin * R2 / (R1 + R2 )

From the above equation, we can deduce the value of R2 as

R2 = Vout * R1 / (Vin – Vout)

Where R1 = known resistance

R2 = Unknown resistance

Vin = voltage produced at the 5V pin of Arduino

Vout = voltage at R2 with respect to ground.

Note: the value of known resistance (R1) chosen is 470Ω, but the users should replace it with the resistance value of resistor they have chosen.

Step 4: The Code:

#include <LiquidCrystal.h>
//LiquidCrystal(rs, sc, d4, d5, d6, d7) 
LiquidCrystal lcd(12, 11, 5, 4, 3, 2);
const int analogPin = 0;
int analogval = 0;
int vin = 5;
float buff = 0;
float vout = 0;
float R1 = 0;
float R2 = 470;
void setup() {
  lcd.begin(16, 2);
}
void loop() {
  analogval = analogRead(analogPin);
  if (analogval) {
    buff = analogval * vin;
    vout = (buff) / 1024.0;
    if (vout > 0.9) {
      buff = (vin / vout) - 1;
      R1 = R2 * buff;
      lcd.setCursor(0, 0);
      lcd.print("  -Resistance-");
      lcd.setCursor(0, 1);
      if ((R1) > 999) {
        lcd.print("   ");
        lcd.print(R1 / 1000);
        lcd.print("K ohm");
      }
      else {
        lcd.print("     ");
        lcd.print(round(R1));
        lcd.print(" ohm");
      }
      delay(1000);
      lcd.clear();
    }
    else {
      lcd.setCursor(0, 0);
      lcd.print(" ! Put Resistor");
      lcd.setCursor(0, 1);
    }
  }
}

Step 5: Conclusion:

This circuit with the R1 being 470 ohm will work fine between 100Ohm to 2k ohm of resistances. You can change the value of the known resistance for higher values of unknown resistances.

Hope you liked this tutorial.

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