How to measure the voltage of battery using Arduino built-in voltmeter?

Other Hardware General Electronics
1

I want to simply measure the voltage of a AA battery using Arduino Uno, but I don't know how to hook up the wires to do so. Do I need to connect the negative terminal from the battery to GND pin of the Arduino Uno? Do I need to use 5V or 3.3V pin of the Arduino Uno? Any advice would be helpful. Thanks in advance!

2

You need to connect indeed the negative terminal to GND.
Then you take 2 resistors of 10K in series and you connect these between the GND and the positive terminal.
That is a voltage divider (google for a picture)
Now you can measure with analogRead() between the two resistors and you should see half the voltage of the battery. The resistors prevent a big current that can damage your duino.

3

Thanks! It worked!!

4

If you have e.g. a 24 Volt power source you should make a voltage divider that does not divide 1:1 but 1:

e.g. +24 --- 50K ---*---- 10K ---GND (total 60K) so after measuring at the star you get 10/60 * 24 ~4Volt.

5

i measured the voltage of the arduino using analogread(),and connected pull down resistors ,,,but i cant measure the voltage of an external battery ??do i any more code correction or any circuit ??help me!!

6

raghul_emcee, post your code.
You should be able to connect a battery with less than 5V direct to an analog input (battery +) and Gnd (battery -) on a 5V powered Arduino and get a reading from 0 to 1023:

void setup(){
Serial.begin(9600);
}
void loop(){
Serial.println(analogRead(A0));
delay(1000);
}