Documentation
Macroelectronics
Rotary encoder

Rotary encoder

Visit the official repository to download the example code and get the latest version.

A 15× scale replica of the Grove Rotary Angle Sensor from the Seeed Studio TinyGo XIAO Starter Kit: 3D printed, wired up, and built around a real potentiometer hidden inside the knob.

The finished giant rotary sensor, gray body with a large black knurled knob on top and copper-tape connector pads on the blue base plate below.

The finished sensor. Twist the giant knob, and it turns a real potentiometer underneath.

The concept

The Grove rotary angle sensor is a simple 3-pin analog input: a potentiometer in a small plastic housing, wired to GND, VCC, and SIG (the Grove connector reserves a fourth pin, NC, not connected). It’s the kind of first component people wire up when they’re learning what an ADC reading even means.

The giant version keeps that lesson intact at 15× scale: a real, tiny linear potentiometer (B10K) sits soldered inside the knob, and its three legs are routed out to giant, solderable copper-tape pads on the base plate, laid out in the same GND / VCC / NC / SIG order as the original Grove connector.

The giant rotary sensor next to a giant XIAO ESP32-C3 board, for scale.

Next to its giant XIAO sibling. Same 15× scale, same idea: real components, giant terminals.

Step 1: the base plate

The base plate is split into four printed quadrants (so it fits on a normal 3D printer bed, one big enough won’t need the split at all). Each quadrant locks into its neighbors with a notch, and a small separate key piece bridges the seam and keeps the joint from flexing.

Two base plate quadrants apart on the table, with the small black key piece sitting between them.
The key piece glued into the seam between two quadrants, bridging the joint.

Each seam gets its own key piece, glued in with cyanoacrylate (CA) glue.

Glue every seam and every key piece with CA glue, then let the four quadrants cure into one solid plate.

The fully assembled base plate, front side, showing the J1 connector silkscreen and the ROTATION label around the central cutout.
The back of the assembled base plate, showing the Rotary Angle Sensor v1.2 label, the logo, and the GND/VCC/NC/SIG pin labels.

The finished plate, front and back. The square cutout in the middle is where the potentiometer body will sit.

Step 2: centering collar

A small printed collar glues into the central cutout, between the base plate and the potentiometer body. Its only job is to center the body so it sits flush and square once it’s glued down in step 4.

The collar frame glued around the central square cutout in the base plate.

Step 3: wiring

Four wires need to run from the potentiometer, through the collar, down through the base plate, and out to the back pads. The base plate has a small hole for each wire.

The back of the base plate showing the four small square holes for GND, VCC, NC, and SIG, with one wire already threaded through.

Thread the wires through from the front. A pair of tweezers or fine pliers helps push them through the tight holes. Leave the wires noticeably longer than you think you’ll need: it’s much easier to trim excess later than to redo a wire that turned out too short.

Four wires (red, brown, blue, and another) coming up through the collar’s central hole, left long, before being routed down to the back.
The back of the plate with the wires pulled through their holes, being trimmed to length with flush cutters.

Step 4: gluing the potentiometer body

With the wires routed, glue the potentiometer body onto the base plate, over the centering collar from step 2.

The gray potentiometer body glued onto the base plate, with the wire bundle coming up through its center hole.

Step 5: decorative pins

Three small pins glue onto the front edge of the body, echoing the three exposed legs of the original Grove sensor’s potentiometer.

Three gray decorative pins glued onto the front of the potentiometer body.

Step 6: bearing wells (optional)

The body has four wells sized for standard 608 bearings (skateboard bearings), meant to help the knob spin smoothly. In practice they turned out not to be fully necessary: the potentiometer’s own shaft holds up the knob fine on its own. Consider this step optional.

The inside of the potentiometer body, showing four bearing wells with bearings seated in them, and the central slot for the real potentiometer.
Close-up of one bearing seated in its well, marked 608Z / ABEC5.

Step 7: soldering the real potentiometer

Solder the real potentiometer (a linear B10K) into the slot in the middle of the body, one wire per leg. Once it’s soldered in, gently pull on each wire from the back of the base plate to take up the slack left in step 3 and get the length just right.

The real potentiometer soldered into place inside the body, wires routed out to the sides.

Step 8: copper tape pads

The last step is turning the wire ends into solderable, touchable pads on the back of the base plate, the same way the giant XIAO’s pins work: copper tape pressed into each shallow pad recess.

Strip each wire and route it into the outermost hole of its pad (the SIG, GND, and VCC pads all carry a wire; NC doesn’t need one, since it isn’t connected on the real sensor either). Make sure the bare wire touches the copper once the tape goes down.

A copper tape circle applied over the GND pad, with the stripped wire poking through and touching the copper.
The SIG and NC pads: SIG has a wire threaded through and touching the copper, NC is just taped over with no wire.

Cutting clean circles and squares out of copper tape by hand is fiddly: a cutting plotter (a Silhouette or similar craft vinyl cutter) makes much cleaner pads than scissors, and it’s worth the patience to set up the cut file correctly before committing the tape.

The finished back of the base plate, all six copper pads in place: two decorative pads plus GND, VCC, NC, and SIG.

The result

Close-up of the finished connector row (J1) next to the knob, with clean copper pads and the decorative pins visible.
The giant rotary sensor next to the giant XIAO with its swappable interior open, for scale.

Bill of materials

  • Standard PLA filament (blue for the base plate, gray and black for the body and knob)
  • Cyanoacrylate (CA) glue
  • Copper tape
  • Stranded wire, four colors
  • A linear potentiometer, B10K (10 kΩ)
  • Four 608 bearings (ABEC5 or similar), optional
  • A cutting plotter (Silhouette or similar), optional but recommended for the copper pads

Files

The printable parts live in this folder: groove_rotary_angle.STL, or split into four separate print jobs as groove_rotary_angle_1.3mf through groove_rotary_angle_4.3mf (with groove_rotary_angle.3mf as the combined project file, and groove_rotary_angle.DXF for the flat profile).

Once wired up, it reads just like the real Grove rotary sensor: GND and VCC to power, SIG to an ADC pin. See examples/rotary for TinyGo firmware that reads it and drives a WS2812 strip with the result.

docs