Soldering the Components

Only a few connections are required. Notice however, this project has wires connected from the opposite side than you might normally expect: they approach from under the board and are soldered on top.

Tethered (USB Only) Connections

These are the connections for a tethered project (no battery or power switch):

STEMMA Wire Color (or Trellis Edge Pad) - Feather Pin

  • Black (GND) - GND
  • Red (VIN) - USB
  • White (SDA) - SDA
  • Green (SCL) - SCL

Here’s how the wiring looks with a STEMMA cable on a Feather M4 board to be used in a “tethered” configuration.

Wires approach from the bottom and are soldered on top. This is important later.

Standalone Connections

A wireless or standalone configuration requires adding a battery and DPDT panel-mount switch. The latter has six pins, but we’ll only be using four. The pinout is symmetrical, doesn’t matter if you have it turned 180°.

Three extra wires are required. If using the STEMMA cable, the trimmed-off bits are just long enough for this.

A wireless Trellis can still operate over USB if desired, but still must use the power switch regardless.

STEMMA Wire (or Trellis Edge Pad)

Feather Pin

Switch Pin

Black (GND)


Red (VIN)

Top Right

White (SDA)


Green (SCL)



Top Center


Bottom Left


Bottom Center

Notice there are two GND connections that must be made to the Feather board. More on that in a moment…

Here’s a back-side view of the switch, showing where wires will connect.

Here’s how the wiring looks with a STEMMA cable on a board to be used in a wireless configuration.

Wires approach from the bottom and are soldered on top. This is important later.

Some Feather boards have a single GND pin, others have more than one.

A switched project requires two GND connections. If your Feather only has one GND pin, the STEMMA wires are thin enough that you can twist two together before tinning the ends, and still have it fit through the single GND connection.

NeoTrellis 8x8 Kit Only

If building an 8x8 setup, some extra soldering steps are required…

An 8x8 setup is comprised of four 4x4 NeoTrellis…es? NeoTrelli?

Use blobs of solder across the A0–A4 pads to assign each 4x4 NeoTrellis a unique I2C address. Usually this involves leaving one untouched, bridging “A0” on the second, “A1” on the third, and both A0+A1 on the fourth (though you can use whatever combination you want, as long as each is unique…it’s configurable in software).

The four sub-Trelloids then need to be soldered together by joining the five pads along their common edges (SDA, SCL, etc.). Although it’s possible to do this with just solder alone, you’ll likely find it both easier and more durable to solder small pieces of bare wire across these pads.

That’s it for the soldering! You can switch off your iron now.

Trim away any excess wire protruding from the top of the board.

For wireless projects, plug in the LiPoly battery and confirm that the Feather board’s power LED turns on with the switch in one position, and that the yellow charge LED is on when connected to USB.

This guide was first published on Aug 28, 2019. It was last updated on May 18, 2024.

This page (Soldering) was last updated on Mar 08, 2024.

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