Electrical characteristic sensors measure the voltage and amperage of the electric current. When the voltage and current sensors are used concurrently, the consumed power of the device can be determined. Electrical characteristic sensors can determine whether the device's circuit is working correctly. Different sensor circuits must be used to measure direct current (DC) and alternating current (AC). If the parameters of the mains are to be measured, it must be done using transformers for safety reasons.

A voltage sensor is a device or circuit for voltage measurement. A simple DC (direct current) voltage sensor consists of a voltage divider circuit with an optional amplifier for a tiny voltage measure. For measuring the AC (alternating current), the input is connected to the rectifier diode or bridge to rectify AC to DC and a capacitor to flatten the voltage. The resulting voltage can be measured with an analogue digital converter of the microcontroller. For safety, while measuring the mains voltage, an optoelectrical isolator should be added at the output, or a transformer should lower the voltage at the input.
A voltage sensor can detect a power failure and measure if the voltage is in the range required. IoT applications include monitoring appliances, power lines, and power supplies.
Sample voltage sensor module is present in figure 1 and schematic connection to the Arduino Uno in figure 2.

The example code:

//Define an analogue A1 pin for voltage sensor
int voltagePin = A1; 
//The result of the analogue reading from the voltage sensor
int voltageReading;  
 
float vout = 0.0;
float vin = 0.0;
float R1 = 30000.0; //  30 kΩ resistor 
float R2 = 7500.0; //  7.5 kΩ resistor
 
void setup()
{
    //Begin serial communication
    Serial.begin(9600);  
    //Initialize the analogue pin as an input
    pinMode(voltagePin, INPUT); 
}
 
void loop()
{
    //Read the value of the voltage sensor
    voltageReading = analogRead(voltagePin); 
    vout = (voltageReading * 5.0) / 1024.0;
    vin = vout / (R2/(R1+R2));
 
    Serial.print("Voltage is: ");
    //Print out the value of the voltage to the serial monitor
    Serial.println(vin); 
    delay(10); //Short delay
}

A current sensor is a device or a circuit for current measurement. A simple DC sensor consists of a high-power resistor with low resistance. The current value is obtained by measuring the voltage on the resistor and applying a formula derived from Ohm's law. Other non-invasive measurement methods involve hall effect sensors for DC and AC and inductive coils (current transformer) for AC.
Current sensors determine the power consumption and detect whether the device is turned on or shorted.
Sample current sensor modules are present in figures 3 and 4, and schematic connection to the Arduino Uno in figure 5

The example code:

//Define an analogue A0 pin for current sensor
const int currentPin = A0; 
//Scale factor of the sensor use 100 for 20 A Module and 66 for 30 A Module
int mVperAmp = 185; 
int currentReading;
int ACSoffset = 2500; 
double voltage;
double current;
 
void setup(){ 
 Serial.begin(9600);
}
 
void loop(){
 
 currentReading = analogRead(currentPin);
 Voltage = (currentReading / 1024.0) * 5000; //Gets you mV
 Current = ((Voltage - ACSoffset) / mVperAmp); //Calculating current value
 
 Serial.print("Raw Value = " ); //Shows pre-scaled value 
 Serial.print(currentReading); 
 Serial.print("\t Current = "); //Shows the voltage measured
 //The '3' after current allows to display 3 digits after the decimal point
 Serial.println(Current,3); 
 delay(1000); //Short delay