I am making a simple Li-Ion battery Tester. Basically its two 5R1 resistor in series and a relay (used to cut off the battery when it reaches cutoff voltage). Arduino is connected with ground to the battery and with A3 to the end of the resistors. But when I try to read the analog value, I receive something like 870, which is about 4.24V. BUT the real voltage is about 3.90V (according to my multimeter). How is that possible? Thanks for any suggestions. – Majenko
Oct 5 '15 at 18:35
• Basically I am trying to read the battery voltage, using A3 on Arduino Nano, but it show higher value than it is supposed, which is really weird. Oct 5 '15 at 19:02
• How are you powering the Arduino? How are you calculating the voltage?
– Majenko
Oct 5 '15 at 19:04
• I am powering it from USB wall socket; I measured it and it outputs 4.92V. Well I am calculation the voltage by multiplying analogRead * 0,00488281 Oct 5 '15 at 19:06
• Well, with those figures I calculate it at (870/1023*4.92) 4.184V. How much do you trust your multimeter?
– Majenko
Oct 5 '15 at 19:09