Potentiometers

[EricVanWyk]

Originally Posted by 1951-44U

Is there any limit to the resistance that a potentiometer wired up to the Analog Breakout can have?

Not really. Just about anything you can find on the shelf is likely to work. I'd recommend choosing something in the 2k-20k range.

The lower limit is set by how much power can be drawn. Lower resistance draws more power (Power = (5 Volts)^2 / R Ohms). You have about 1W total to play with, which would limit you to 25 Ohms - but that would be kinda silly. Why waste all that power? 1k is good enough lower bound here: 25mW.



As you increase pot resistance, your power consumption goes down but you become more sensitive to other sources of error. The one that will eventually limit you is the input impedence of the NI-9201 - it draws a tiny amount of current to measure the voltage, which can affect the voltage that it is measuring! As a rule of thumb, you want this to be about an order of magnitude of margin. Fortunately, the NI-9201 has a really nice input impedence of 1 mega-ohm. If your pot is less than 100k, you won't even notice it.

EDIT: Gah, beaten by Marshall again!