Electrical – No output voltage on wiper when using pot as voltage divider

potentiometervoltage divider

I've been trying to teach myself about potentiometers and how they can be used as voltage dividers. I bought some Alpha 10k linear pots to use in a really basic test circuit. I intended to connect the pot to my breadboard but unfortunately it doesn't fit so I've soldered some spare jumper wires to the pins of the pot.

In my circuit I have power from my Arduino Uno board (3.3v) connected to the leftmost pin on the pot and the other outer pin on the right is connected to ground. The middle pin (which I've assumed is the wiper) is connected to ground as well. When I measure the voltage between the two outer pins it's consistently about (3.2v) as I would expect but when I measure the output voltage between the wiper and ground it's either 0 or moves randomly between different values regardless of where I've turned the knob to.
I'm wondering if I've misunderstood how the pot should be wired in this configuration or if it's just a case of bad soldering?

Circuit diagram

Best Answer

A potentiometer works in the same way as a simple two resistor potential divider, so here on the left is the equivalent of the schematic on the right showing a potentiometer. The middle output being the wiper of the potentiometer. On the physical potentiometer itself the middle pin is usually the wiper but I would recommend that you check that with a data sheet for the potentiometer.

I hope that this clears up the connections and just for extra knowledge here is a formula which will work to calculate the output voltage from the resistance of the two resistors either side of the output:

$$\mathrm{Voltage\space Out} = \mathrm{Voltage\space In} \times \left(\frac{R_2}{R_1+R_2}\right)$$

schematic

simulate this circuit – Schematic created using CircuitLab