DC Voltmeter {HELP!}

Other Hardware Sensors
1

Good afternoon all,

So I want to make a voltmeter using Arduino UNO. whenever i use the internal voltage source (The 5V and 3.3V ) it gives me a kind of correct answer but whenever i use an external voltage source, ie a battery or a dc generator it gives me the max analog value (1023).

I am using a voltage divider with R1= 100Kohm and R2= 10Kohm

Here is the code.

int analogInput = A0;
int value = 0;
float R1=100000.0;
float R2=10000.0;
float R3=5.0;
float vin=0.0;
float vout=0.0;
float current=0.0;

void setup(){
pinMode(analogInput, INPUT);
Serial.begin(9600);
}
void loop(){

value = analogRead(analogInput);
vin= value*5.0/1023.0;
vout= vin/(R2/(R1+R2));
current = vout/R3;
Serial.println(vout);
delay(500);
}

2

Please post schematic of your circuit (real schematic, not Fritzy wire diagram - hand drawn is fine). Most likely there's an error in your wiring.

3

Thank you sir! I have figured it out! I didn't connect the R2 to the Arduino's GND...