Determining terminals of a potentiometer

Forum 2005-2010 (read only) Hardware Interfacing
1

Hey guys,

I bought a potentiometer today, being a noob i forgot to ask which terminal is anode and which is cathode, there are no markings on the knobs. how can i figure out which terminal is which?

2

A potentiometer usually has no anode or cathode. Polarity usually does not matter for potentiometers.

3

http://www.arduino.cc/en/Tutorial/Knob

so using this tutorial,

The potentiometer should be wired so that its two outer pins are connected to power (+5V) and ground, and its middle pin is connected to analog input 0 on the Arduino.

can i use either outer pin for the connection? and is there something that i should keep in mind in case of damaging the arduino?

4

Generally, one outer pin is connected to +V. The other is connected to Gnd. The middle pin is connected to an analog input pin.

As long as the resistance level of the potentiometer is high enough, no damage will occur.

What is high enough? Mr Ohm figured that out a long time ago. V = IR. R is the resistance value of the potentiometer. V is the voltage of the Arduino. I is the current level. As long as I is fairly small, 20mA is a good upper limit, no damage will occur.

5

Another point to add to Paul's description: it does matter which end you connect to Vcc.

Hold the pot so the shaft is pointing toward you, and the terminals are below it.

If you're using the pot as a voltage divider, you will usually want to connect the left terminal to ground, the right terminal to the voltage to be divided, and the center terminal to whatever is using the divided voltage. This makes the output voltage increase as you turn the knob clockwise, which is what users will normally expect.

Ran

6

And if you reverse the connections of the outer terminals, the voltage changes in the other direction.

So it really does matter which way you connect them, when you are designing the usage. (Think of a volume knob!)

7

However with the software map command available, it doesn't matter again because you can have the resulting variable increasing or decreasing in either pot turn direction you want regardless of which pot end terminal is grounded.

Lefty

8

Ah, I did not think of that. And of course there are logarithmic potentiometers as well. Then the direction does of course matter.

But still, there is not "anode" or "cathode"

Cheers, Udo