I am trying to make my Arduino to work as an online multimeter. At the beginning, I'm trying to make it a voltmeter. I'm simply trying this tutorial: "http://tiny.cc,93515".
I've done exactly the same as the tutorial I'm following, with three exceptions:
I'm not using an LCD monitor.
I'm using R1 = 25 kilo-ohms and R2 = 5 kilo-ohms.
I'm trying to make it an online voltmeter, so there is an Ethernet shield attached to it.
The problem is, whenever I'm giving about 3-4 volts DC input to the circuit, I'm watching on the serial monitor that the Arduino has measured 10-11 volts! When the input voltage is 10-11 volts, the serial monitor shows 16-17 volts. Whenever I give the maximum input of 27 volts (my power source is old, so does not reach the 30 volts maximum), the serial monitor is showing 28 volts!
So, I think that there is an offset in the ATmega328 which I need to remove.
Could anyone please help?
Thanks in advance.