Hi @Gentmat

Your english is fineâ€“donâ€™t worry! You can use any value that makes the measurements in the range you want to measure, upto a limit imposed by the input impedance of the analog to digital converter on the core (around 40k min).

Letâ€™s say you measure your FSR and you know it ranges from 10k ohm under the lightest load to around 500 ohms under the heaviest load.

With a 1k fixed resistor we would have

Light load: 3.3/(1000+10000) = 0.3mA so the resistors would have 1000*0.3mA = 0.3V and 10000*0.3mA = 3.0V across them. The ADC divides 0 to 3.3V in 4095 steps or 0.80586 mV/step, so the reading could 3728 or 372 depending on which resistor was on the top or bottom.

Heavy load: 3.3(1000+500) = 2.2mA so we would have 2.2V and 1.1V across the two resistors and the readings would be 2730 and 1330 depending.

So our span of values from light to heavy is about 1000 ADC steps in the range we are interested in.

Now lets do the same math for a 10k fixed resistor:

Light load: 3.3(10k+10k) = 0.165mA and we would have 1.65 V across both the fixed and FSR resistors. This would mean an ADC reading of 2048 no matter which one was up or down since they are the same value at the load.

Heavy load: 3.3(10k+500) = 0.3143mA and 3.1429V on the 10k and 0.1571V on the FSR. The values would be 3900 or 195 depending on which one was on top.

So the span from light to heavy is now about 1800 ADC steps and we have more potential resolution.

So you can divide the FSR range into 1000 steps or 1800 steps. My experience with these is that more steps is not always better since the repeatability of the device with a given load is somewhat limited. But now you know how to figure it out, I hope!