Analog resistance isn't the only thing you can calculate with the Raspberry Pi Zero GPIO. You can also capture the voltage levels from something like a low dropout voltage regulator. These regulators will work even when the input voltage is very close to the output voltage. By reading the sensor, we can read values of things such as rechargeable battery packs.
We can demonstrate this concept with only a variable resistor and a 1 uF capacitor. I used the 10K variable resistor included in the Elego kit.
With the following circuit, we can control the voltage divider from the 3.3 volt Raspberry Pi Zero output and read its value. As you can see, it is just like the previous recipe on resistive sensors. This time, we will track the voltage instead.
If you were measuring higher voltages, you would use a higher capacitor value to be able to more accurately track the discharge time. It's how we determine the voltage value this time, but timing...