Take the HSTS016L model as an example, it is capable of measuring current values from 10A to 200A. Using the split core current sensor type, we can turn the CT on and off without changing the existing system, and just use a clip to put the measuring cable inside the CT. The output voltage of this sensor is 2.5V +/- 0.625V, which is a good accuracy. Although the voltage output range of this sensor is between 1.875V and 3.125V, it is also suitable for 3.3V analog sensors, especially Arduino Nano and NodeMCU microcontrollers.
The sensor has 4 output pins: RED (5V input), BLACK (0V Gnd), YELLOW (Analog Output), and WHITE (Analog for Calibration). Sometimes the supply voltage may not be exact 5V thus we will need additional Analog Pin to measure the exact middle point from the White Pin. For Arduino UNO, there are 6 analog input pins (A0-A5) where we can use one of the pins to measure AC current and 1 more to use for calibration purpose. The analog input pins will map input voltages between 0 and 5V into integer values between 0 and 1023 with resolution of 4.9mV per unit (5.00V / 1023 units).
We connect RED to 5V input, BLACK to ground, YELLOW to analog pin A1, and WHITE to analog pin A2. It is highly recommended to use a 12V power adapter to power the Arduino Uno and the sensor. Using a 5V power supply over USB will have an initial offset value, you may need to manually add the offset value when uploading the code.
// Which pin to measure Current Value (A0 is reserved for LCD Display Shield Button function)
int currentAnalogInputPin = A1;
// Which pin to calibrate offset middle value
int calibrationPin = A2;
// Key in value to manually offset the initial value
float manualOffset = 0.00;
// If using “Hall-Effect” Current Transformer, key in value using this formula: mVperAmp = maximum voltage range (in milli volt) / current rating of CT
float mVperAmpValue = 12.5;
// Analog input pin maximum supply voltage, Arduino Uno or Mega is 5000mV while Arduino Nano or Node MCU is 3300mV
float supplyVoltage = 5000;
/* to read the value of a sample for offset purpose later */
float offsetSampleRead = 0;
/* to read the value of a sample including currentOffset1 value*/
float currentSampleRead = 0;
/* to count time for each sample. Technically 1 milli second 1 sample is taken */
float currentLastSample = 0;
/* accumulation of sample readings */
float currentSampleSum = 0;
/* to count number of sample. */
float currentSampleCount = 0;
/* to calculate the average value from all samples, in analog values*/
float currentMean ;
/* square roof of currentMean, in analog values */
float RMSCurrentMean ;
/* the final RMS current reading*/
float FinalRMSCurrent ;
void setup() /*codes to run once */
{
Serial.begin(9600); /* to display readings in Serial Monitor at 9600 baud rates */
}
void loop()
{
/* 1- AC & DC Current Measurement */
if(micros() >= currentLastSample + 200) /* every 0.2 milli second taking 1 reading */
{
/* read the sample value including offset value*/
currentSampleRead = analogRead(currentAnalogInputPin)-analogRead(calibrationPin);
/* accumulate total analog values for each sample readings*/
currentSampleSum = currentSampleSum + sq(currentSampleRead) ;
/* to count and move on to the next following count */
currentSampleCount = currentSampleCount + 1;
/* to reset the time again so that next cycle can start again*/
currentLastSample = micros();
}
/* after 4000 count or 800 milli seconds (0.8 second), do this following codes*/
if(currentSampleCount == 4000)
{
/* average accumulated analog values*/
currentMean = currentSampleSum/currentSampleCount;
/* square root of the average value*/
RMSCurrentMean = sqrt(currentMean);
/* calculate the final RMS current*/
FinalRMSCurrent = (((RMSCurrentMean /1023) *supplyVoltage) /mVperAmpValue)- manualOffset;
/* if the current detected is less than or up to 1%, set current value to 0A*/
if(FinalRMSCurrent <= (625/mVperAmpValue/100))
{ FinalRMSCurrent =0; }
Serial.print(” The Current RMS value is: “);
Serial.print(FinalRMSCurrent,decimalPrecision);
Serial.println(” A “);
currentSampleSum =0; /* to reset accumulate sample values for the next cycle */
currentSampleCount=0; /* to reset number of sample for the next cycle */
}
}
