I currently have a project where I need to determine the value of a resistor in a voltage divider circuit.

The formula I am using is the following:

r2 = (-v1*r1)/(v1-v2)

When I check the values of the voltage of this circuit using 18 bit, this is my result using 330 ohm resistor on r1:

v1 v2 r1 r2 r2 (calculated)

3.175119 3.299596 330 15,000 8417.533119

For the purpose of this test, I do know the value of r2 (15,000 ohms) but in application I won't know. I see the schematic for ADCPi plus shows 10k, vout, 6.8k on the voltage divider, but how I would verify the resistance of the board?

My feeling is that r2 is being affected by the input resistance in the voltage divider on the ADCPi plus board. Can you give any insight into the problem I am having?

Your assistance would be extremely helpful,.