can i make a voltmeter just with an arduino?
yes, even a 6 channel voltmeter, looks like
//
// FILE: Voltmeter.pde
// AUTHOR: Rob Tillaart
// DATE: 2012-12-27
//
// PUPROSE: 6 channel voltmeter
//
int pin[] = { A0,A1,A2,A3,A4,A5 };
void setup()
{
Serial.begin(115200);
}
void loop()
{
for (int i=0; i<6; i++)
{
analogRead(pin[i]);
float voltage = analogRead(pin[i])*5.0/1023;
Serial.print(voltage, 3);
Serial.print("\t");
}
Serial.println();
// delay(100);
}
Output can easily be copied into Excel or so.