Voltage Measurement using ArduinoThe voltage measurement using Arduino the input voltage is must in range 0 to 5v. It’s achieved using below circuit. AC voltage is step down with help of voltage transformer, its primary winding is connected across the supply and its secondary winding is connected to voltage divider circuit for reduced further voltage level.

Voltage sensor circuit

Transformer –

Step-down transformer

The step-down converters are used for converting the high voltage into low voltage. The converter with output voltage less than the input voltage is called as a step-down converter, and the converter with output voltage greater than the input voltage is called as step-up converter. There are step-up and step-down transformers which are used to step up or step down the voltage levels. 230V AC is converted into 12V AC using a step-down transformer. 12V output of step-down transformer is an RMS value and its peak value is given by the product of square root of two with RMS value, which is approximately 17V.

Voltage divider 1 for step down voltage level :-A voltage divider is a simple circuit which turns a large voltage into a smaller one. Using just two series resistors and an input voltage, we can create an output voltage that is a fraction of the input.

Formula of voltage divider is vout = vin *R1

R1+R2

vin =12

R2 = 100Ω

R1 = 10Ω

vout = 12 *10

10+100 = 1.09

so positive voltage is 1.09 and negative voltage is 1.09.(due to AC voltage)

Voltage divider 2 for eliminating negative portion of AC voltage :-vin =5

R2 = 470 kΩ

R1 = 470 kΩ

vout = 5 *470

470+470 = 2.5

but this voltage divider directly connected to voltage divider 1.In this connection resultant voltage is adding.

So resultant voltage at A-B point in positive ac portion is

Voltage divider 1+ Voltage divider 2

= 1.09 + 2.5 = 3.59 ------(1)

And resultant voltage at A-B point in negative ac portion is (due to negative ac portion Voltage divider 1 output negative)

Voltage divider 1+ Voltage divider 2

= -1.09 + 2.5 = 1.41 -------(2)

Output of equation (1) and (2) are less than 5v and greater than 0v so we interface to Arduino because of Arduino operating voltage range is 0 to 5 v dc.