potentiometertransistors
From what I know, potentiometers vary an analog current with an input usually in the form of a knob. And transistors vary an analog current with an input in the form of a smaller current.
Is there any practical difference between the two other than one varies between the position of a knob and the other varies between a smaller current?
You could use a potentiometer (pot) for this, but they are typically continuous in their output where it sounds like what you want is discrete values. To use a pot you would need to use it in a voltage divider and set bins (voltage ranges) for the various values you want to set to, and read in the output of the divider with an ADC. To set this you would adjust the pot until value of the output falls in to one of the bins. This person made a pretty neat feedback system for this idea. You can also buy pots with detents, detents are mechanically set positions through the turn.
Alternatively you can use a rotary encoder, they're those knobs that spin forever in either direction and "click" in to set positions along the way, also by use of a detent. There is a wide variation in encoders. I've recently used these ones. Basically you can continue turning these around and around and they send pulses to your microcontroller letting it know which way they are turning (this is a slide set explaining how they work). By counting these turns in the respective directions your microcontroller can set values. For instance turning right increments the value while left decrements. This is nice when you want to use one knob to set variable ranges, a solution you can drop in to most projects that need a knob.
The slot is for adjustment with a flat-headed screwdriver (instead of a knob), and is not generally intended as a feature for the knob to engage with. Just use the same type of knob that you'd use with a purely cylindrical shaft - a knob with a setscrew:
Best Answer
They are entirely different.
Any resistor is a linear device, a transistor is nonlinear. A linear device has a linear relationship between voltage and current, simply put. Transistors show very much more complex behavior.
One is an interface, the other not. You cannot twiddle a transistor to change its characteristics.
A potentiometer is used to change a setting of a device, permanently at production, or during use. As long as it is not touched, the setting stays the same, being a passive device. Transistors can't be used to do that.
A transistor, being an active device, puts some of its characteristics, say the output resistance in relation to one of its inputs, say the collector current.
A transistor does exhibit resistance in the sense there is a voltage and a current, and when I measure those, it looks like a resistance. But when you change the CE-voltage, the current will not change in the same ratio. Say, you double CE-voltage, you will not get double the current, but rather nearly the same current mostly, making it a differential resistance. On any resistor, you would get a linear response, double voltage ==> double current.
This leads to the possibility of self-feedback on a transistor, making it possible to really regulate something, say in a constant current source. Twice the voltage, same current? Completely impossible with only passive devices, no resistor can do that.