# Measurement of Low value resistance (0.1 to 50 Ohm)

The previous voltage divider design is suitable for only measurement of higher values of resistance (50 Ohm to 1 MOhm) to measure very small value resistance we have built this circuit, it consists of constant current source of 100mAmp. Measuring voltage drop across a resistor having constant current gives us resistance value (R = V / I).
Calculations
V = I x R
R = V / I
Where:
I = 100mAmp as we are using constant current source of 100mAmp
V = Measured by Arduino
Constant current source is built using LM317
Iconst = Vref / R where: Vref of LM317 is 1.25V
Iconst = 1.25 / R
Iconst = 104mAmp

## Low Resistance (0.1 to 50 Ohm) Measurement Arduino Code

```/*
Resistance Measurement (0.1 to 50 Ohm)- www.circuits4you.com
result to the serial monitor.
*/

// the setup routine runs once when you press reset:
void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
// read the input on analog pin 0:

// Convert the analog reading (which goes from 0 - 1023) to a voltage (0 - 5V):
float voltage = sensorValue * (5.0 / 1024.0);

float Rx = voltage / 0.104;

// print out the value you read:
Serial.print("Resistance:");
Serial.print(Rx);
Serial.println(" Ohms");
delay(1000);
}
```

## Result of Resistance Measurement

Open the serial terminal and see the resistance value. This code and circuit will not work for values more than 50 Ohm as 50 * 100mA = greater than 5V.

## 2 thoughts on “Measurement of Low value resistance (0.1 to 50 Ohm)”

1. Malosse says:

Hello

Is it possible to reduce constant courant source to 10mA ?

Manu

1. Manoj R. Thakur says:

When we reduce current voltage drop across resistance becomes small, you can reduce it.. Use differential amplifier to amplify voltage across resistor. Read more on bridge circuit for resistance measurement.