Calculating resistor values to measure any DC voltage using Arduino

Calculating resistor values to measure any DC voltage using Arduino

The calculation in this article is shown in the video https://youtu.be/t8xwrVj2aFs to measure any DC voltage with Arduino. 

Voltage divider is used to calculate the the voltage for Arduino voltage sensor as shown in Fig. 1

In this figure we have got:

Battery voltage VB

Output voltage that goes to Arduino V1 input pin (i.e A0)

R1 is 30kΩ

R2 is 7.5kΩ

Arduino UNO accepts 5V at the input, therefore V1 is 5V. From this we can find the current I in both R1 and R2. 

I=V/R and therefore I=5/7500=0.000666=666µA 

Because R1 and R2 are in series, the current is the same for both. So IR2 is also  666µA. We can find the voltage across R1 as 

VR1=666µ x 30000=20V.

Now we know the maximum voltage at V1 can be 

VR1+VR2=5V+20V=25V.

Calculating Larger Voltage Values

We can add another resistor in series RX with this circuit as shown in Figure 2.

Figure 2. Series Resistor RX in circuit. 

To find the value of RX for measuring BAT2 Voltage, we have:

RX=BAT2-25666uA

Now We have got the formula for RX, if for example BAT2 = 120V

Then

RX=120-25666uA=95666ua=142.5kΩ

So using a 142kΩ resistor as RX, we can measure up to a maximum of 120V.

Images

voltage-sensor-schematic-1

voltage-sensor-schematic-2

voltage-sensor-schematic-1

voltage-sensor-schematic-2