Negative and positive voltage sensor Arduino

Question

I want build a negative and positive voltage sensor with an Arduino. I found this article: Read Positive and Negative Voltage in Arduino.

There is the circuit I need, but with some modifications. I want to measure cell voltage so I want only voltages around -1.5 V to 1.5 V. So in my case I will use 3.3 V from the Arduino as power supply. I have few questions:

1. What should be the new values of the resistors (please specify one by one) (blue ones)
2. Should the measurement probes be in the positions marked in purple?
3. Did I mark correctly how I will connect the pins (green text)?

Answer 1

This voltage divider will give you the most dynamic range without an amplifier. R1 is chosen to provide a voltage drop of 1.5V at 500uA, so for -1.5V the ADC will see zero. R2 is chosen to drop 3.3V at 500uA. So the ADC input will be 0, 1.06, and 2.12 volts. You can make the values of R1 and R2 equal if you want to have the ADC centered at 1.65V (1/2 Vdd) for 0V input.

^{simulate this circuit – Schematic created using CircuitLab}