The vast majority of shunt resistors have values that are lower than one ohm. Because of their limited range and resolution, measurement instruments are unable to properly measure resistances with such low values. This is because of the limitations of the devices. These are typically tested with resistance bridges, which require a

specific configuration in order to function properly. A circuit that can test resistances ranging from 0.1 to 1 ohm is shown here for your convenience. Circuit and the working Figure show the schematic of the circuit that makes up the milli-ohm meter. The Arduino Uno board (Board1), a low-dropout regulator MIC5219 (IC1), and a 16x2 LCD display are the main components of this circuit (LCD1). A voltage drop takes place across a resistor whenever current flow through it. The magnitude of this drop is proportional to the amount of current that is flowing through the resistor. Using this circuit and using this principle, which is known as Ohm's Law, allows for the measurement of resistance. The test points A and B in the circuit are connected to the resistance that is to be measured, which is connected across those two test points. The voltage drop that occurs across the resistor may be seen on the Arduino board at the analogue pin labeled A0. In order to achieve a higher precision, the analogue reference voltage was changed to an internal reference of 1.1V. The Arduino Uno serves as the circuit's central processing unit (CPU), calculating the circuit's resistance based on the analogue-to-digital (ADC) value and displaying the result on the liquid crystal display (LCD). A constant-current regulator is implemented in IC1's hardware configuration.

Fig. 2: Circuit diagram of milli-ohm meter When the push-to-on switch S1 is activated, the Arduino enables IC1, and the integrated circuit then produces a constant current of 100mA across the test resistor. A voltage drop takes place across the test resistor, the value of which is then displayed on LCD1 after being calculated by the Arduino in accordance with Ohm's Law. The measured resistance shouldn't be higher than one ohm at any point in time. If it is greater than one ohm, a notice that reads "!OL OR NC!" will show on the LCD1 screen. In addition, the component is removed from the circuit anytime the resistance value reaches a threshold that is greater than one ohm. After the measurement, IC1 will be rendered inoperable if the S1 button is pressed again. Atmega328P is the core component of the widely used and widely available open-source microcontroller development board known as Arduino Uno. It includes fourteen digital input/output (I/O) pins, six of which can be used for PWM outputs while the remaining six can be used for analog inputs. In addition, it has the capability of being outfitted with a power jack, USB connector, 16MHz crystal, and ICSP header. Since it already has the Arduino bootloader loaded onto it, there is no requirement for any additional hardware to be able to burn the Atmega chip. The operation of the circuit is determined by the software program that is stored into the internal memory of the Arduino Uno. The Arduino programming language known as Sketch was utilized in the creation of the mR Meter.ino software. The application is compiled and uploaded using an Arduino integrated development environment (IDE).