Calculating resistance with Arduino

Projects Programming
1

I'm trying to measure resistance with arduino Nano ATMega328, it works on paper, but Arduino doesn't somehow calculate the resistance. LCD output: Voltage: 1.73 R1: -24495

Schematic and princible is here (first circuit picture):
http://iwantmyreal.name/blog/2012/09/23/measuring-the-temperature-with-an-arduino-and-a-thermistor/

R3 is in series with R1 to lower 12.08 voltage for arduino, so:
R1 = (R2*Vin)/Vout) - R2 - R3

Code:

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2

What do you think R2 should be? Does that value actually fit in an int?

3

Hi, can you please use code /code tags to post your code.
The link you give is nothing like what you describe.
Can you post a CAD or pic of a hand drawn circuit diagram and if possible a pic of the project.
Hint, float all the values you are using in the sketch.
Hope to help.

Tom...... :slight_smile:

4

Yes, the 17,76 kohm is calculated with Vin 12.08 V and gives 4.3 V Vout when R1 is 500 ohm.

-LS

IMG_4668.JPG
IMG_4668.JPG1600×1200 185 KB

5

Your equation for calculating R1 is wrong. Wikipedia gives a formula for two resistors:
Vout = Z2/(Z2+Z1) - Vin

You have two resistors on the Z1 side, so Z1 = R1 + R3 and Z2 = R2.

Plugging that in gives:
Vout = R2/(R2 + R1 + R3) - Vin.

Vout + Vin = R2/(R2 + R1 + R3)

R2 + R1 + R3 = R2/(Vout + Vin);

R1 = R2/(Vout + Vin) - R2 - R3
which is NOT the equation you have.

6

PaulS:
Wikipedia gives a formula for two resistors:
Vout = Z2/(Z2+Z1) - Vin

Vout = Z2/(Z2+Z1) x Vin

7

Their artwork sucks.

8

Tried this as a part of the code, but it gives still incorrect ansver R1 : -26129

R1 = (R2)/(Vout + Vin) - R2 - R3;

9

Paul's equation is wrong since he misread the equation in Wikipedia.

Tbird, your equation in your pic correctly solves for R1.

10

Thanks, I thought so because I solved it on paper. Thanks for all! Now back to calibration plans.

-LS