So, you’ve decided that your project needs a rotary input, either from a human or as feedback from a machine. Your next step is to choose between your two main options: a potentiometer or an encoder. Both devices will sense the rotation of a shaft, but they operate using different principles, and they both have specific strengths and weaknesses.
Encoder and Potentiometer Basics
The most obvious difference between rotary potentiometers and encoders is that encoders can spin continuously in either direction, while potentiometers can only turn a set distance clockwise or counter-clockwise before they need to stop.
Potentiometer wiring generally consists of:
- Positive voltage on one outer connector
- Ground on the other connector
- Slider connection in between the two that acts as a voltage divider
While multi-turn setups exist, in their most basic form, this middle connection slides between the Vcc and GND extremes. This configuration changes the slider voltage depending on where the contact touches the resistive element.
Encoders act digitally and come in two different forms: Here's a breakdown of absolute vs incremental encoders:
- Absolute encoders can sense their actual angular position based on internal sensing, and they allow users to obtain digital readings.
- Incremental encoders don’t sense position directly, but they do send pulses to the controlling hardware as they rotate.
Be sure to check out our detailed breakdown of the different types of encoders available and learn more about what a potentiometer is.
Analog Potentiometers vs. Digital Encoders
Because of the way they operate, potentiometers are an inherently analog input device, while encoders are digital. As such, encoders have become much more common in recent decades, but potentiometers are still available and useful in many applications. Here are some important features potentiometers offer:
- Control. You can use potentiometers to control other analog electronics in a 0-100% range, such as when you turn a system’s volume up or down.
- Voltage division. You can set up potentiometers to divide voltage in a non-linear manner, which can be very useful for audio applications—since our ears don’t hear changes in sound linearly. If you’re using a potentiometer in a digital system, you’ll need an analog-to-digital converter (ADC) to translate this into a numerical value.
- Simplicity. Because a potentiometer’s voltage output is based solely on position, and a computer doesn’t have to monitor its state for changes continuously, its operation is somewhat akin to an absolute encoder.
While you can use several types of sensors in absolute and incremental encoders, at their heart, they’re both digital devices, sending out 1s and 0s to indicate position. Therefore, you’ll need to use a microcontroller or other digital system with these devices to translate the output. Their digital basis also means that there is normally more work involved to set one up.
On the other hand, encoders can rotate continuously, and many can give excellent resolution. This resolution comes at the expense of computing power, and encoders can be more expensive than their analog counterparts.
Here's a simple stat sheet for potentiometers vs. encoders, breaking things down between incremental and absolute encoders.
Potentiometers:
- Easier to set up than an encoder (assuming ADC capabilities if used in conjunction with a digital system)
- Position is always clear
- Infinitely variable inputs
- Works with analog devices
Encoders (Incremental)
- More difficult to set up than a potentiometer
- Position requires constant monitoring for changes
- Limited number of input positions
- Unlimited left and right rotation
- Inherently digital
Encoders (Absolute)
- More difficult to set up than a potentiometer
- Angular position is always clear
- Limited number of inputs positions
- Unlimited left and right rotation
- Inherently digital
While you can use a potentiometer in analog or digital setups, an encoder will only work in applications where you can monitor them digitally. Both devices are interchangeable in many situations, but if you require a user interface that can spin and spin in one direction or something to monitor a motor that continuously turns, an encoder may be your only choice.
On the other hand, if you need a simple user interface where you can turn a volume knob or monitor a motor with limited range, a potentiometer may be the better option.
As with any engineering decision, each choice comes with its benefits and drawbacks. While encoders have become much more common in recent years, and are in many ways more capable, potentiometers are still very relevant today and may be the best choice in certain situations. For another digital or analog control option, you may want to consider a digital potentiometer, which allows a microcontroller to vary resistance digitally.