The Arduino analog input is limited to a 5 VDC input. If you wish to measure higher voltages, you will need to resort to another means. One way is to use a voltage divider.
It is fundamentally a 5:1 voltage divider using a 30K and a 7.5K Ohm resistor.
Keep in mind, you are restricted to voltages that are less than 25 volts. More than that and you will exceed the voltage limit of your Arduino input.
- GND – This is where you connect the low side of the voltage you are measuring. Caution! : This is the same electrical point as your Arduino ground.
- VCC: The is where you connect the high side of the voltage you are measuring
- S: This connects to your Arduino analog input.
- – (or minus): This connects to your Arduino ground.
- +: This is not connected. It does absolutely nothing… zilch… nada… jack diddly doo doo.
The schematic for this is pretty straight forward. As previously mentioned, its just a couple of resistors. In fact, you could build your own in a pinch.
Find yourself a 9 volt battery and connect it, your voltage sensor module and Arduino as shown below.
Enter the following sketch, upload it and go to town. If you open your Arduino serial monitor you will be able to see the voltage.
DC Voltmeter Using a Voltage Divider
int analogInput = A1;
float vout = 0.0;
float vin = 0.0;
float R1 = 30000.0; //
float R2 = 7500.0; //
int value = 0;
// read the value at analog input
value = analogRead(analogInput);
vout = (value * 5.0) / 1024.0; // see text
vin = vout / (R2/(R1+R2));
Serial.print("INPUT V= ");