Potentiometers and the Arduino Uno

Aidan just shared a new tutorial: "Potentiometers and the Arduino Uno"

Variable resistors come in all shapes and sizes, and they all do the same basic job. They allow you precisely control voltage/current flow within a circuit. The most common type of variable resistor we see in DIY electronics is the Potentiometer, or …

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Just got off the phone with @Trent5487676 and realized I’m missing some basics.

Quick, possibly double question:
These are the resistors I’ve come across so far.
If a pot is just a variable resistor, what is the third leg for?
For instance, in this diagram, the outer pins are connected to power and ground and the inner is connected back into the Arduino. If I discounted the ground pin and then connected the middle pin to ground AND the arduino, would I still be able to read values?


How a potentiometer works is a little tricky to explain via text, but it’s fairly intuitive once you’ve used it once and had that “a-ha moment”. This image shows what is going on inside the multimeter so it might help to make the link.

I’d recommend re-reading the second paragraph of that guide. Then using your multimeter, do a resistance measurement between two of the three pins and sweep the knob back and forth across the range. Do this for each of the combinations of pins on the potentiometer.
I’m pretty confident once you’ve played around measuring what is going on things will make more sense and you’re likely to ever forget, it’s just a bit counter-intuitive at first.

Once you’ve got a handle on how the resistance changes as the potentiometer is adjusted what the voltage is going to do is less of a jump.

I’ll experiment with the multi meter tonight and let you know how I got on. :slight_smile:

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Hi Pixmusix

Short answer is you would read maximum at all times.
Carry out Trents experiment and you should see what is happening. The potentiometer could be likened to 2 variable resistors. As one decreases in value the other increases so the total always equals the total value across the two outer pins. This means the potentiometer nearly always presents a constant load to the source and a voltage is at the junction of the 2 resistors equal to the ratio between the 2 resistor values at any one time.

Any potentiometer can be connected as a single variable resistor by using the centre connection and either one of the outer ones but the uses are very different. This type of connection and the term for this type of resistor is “Rheostat”. Fairly easy to explain and demonstrate face to face but difficult in this environment. The best way is research with Trent’s experiment.
Cheers Bob
Don’t forget that depending a bit on Multimeter quality it could be fairly slow to respond and settle to a reading so be patient.

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