The Circular Soft Potentiometer is a flexible ribbon controller with adhesive backing. It extends the limited range of a standard pot to 2.2 inches, encouraging a larger gesture from the user. The resistance changes from 100 ohms to 10,000 ohms as the user moves their finger in either direction around the circle. It consists of three separate layers that are actuated when pressure is applied. It can be found for purchase at Adafruit and Tinkersphere.
You can find the data sheet here. However, the basics are listed below:
- Standard resistance range: 10k ohms-100k ohms
- Standard resistance tolerance : ±20 %
- Power rating: 1 Watt max. at 25°C
- Ideal operating temperature: -40°C to +50°C
- Connection: solder tabs
Description of example uses
The soft pot is perfect for volume control or scrolling (think: original iPod). It maps to the shape of a normal pot, so it’s a natural transition for the user. Other notable uses are CNC position sensors and throttles for drones.
Since it’s sealed from harsh conditions, like radiation, it’s ideal for medical equipment or airline seating. Unlike a traditional pot that can degrade and break down over time, the SoftPot has a much longer life span.
Strengths and Weaknesses
- Affordable at $7, cheaper than some mechanical pots.
- Installs quick, cheap, and easy with the 3M adhesive backing.
- Versatile in that it works with contact, movement, or human touch.
- Sealed for harsh environments.
- Won’t deteriorate over time.
- Multiples can be used on the same control panel.
- Thinner and sleeker than a mechanical pot.
- Doesn’t add much weight to your project.
- Can customize its resistance and tolerance.
- Would take up a good amount of room on a control panel.
- Solder tabs are close to the plastic strip so they can melt. Wire wrapping might be ideal here.
- Took me awhile to figure out which pin was power and which was ground. Also confusing input with power can melt your component.
- If your finger slips off the three layers the circuit is broken, disrupting the output.
Example Circuit Schematic
Example Microcontroller Code
You can use this sensor with the Arduino Uno to brighten and dim an LED. It’s a good exercise to get a feel for the SoftPot before moving on to more complicated applications.
The code below reads the analog input value, maps it to 0 to 255, and then uses that to control the LED brightness. You’ll notice that if you don’t keep your finger squarely on the sensor, the LED turns off, disrupting the transition from dim to bright.
The solder tabs are closely spaced together- 1.3mm- so wire-wrapping to male header pins is easier than just attaching it to the breadboard. Plus, it gives you an excuse to wire-wrap, which is always a good time.
I’d also like to note that it is possible to touch the SoftPot in different locations. For instance, when I place my finger on the 255 side, the light is at its brightest. But when I place my other finger on the 0 side of the pot at the same time, it dims the LED to about 50%. You can see it in action: