There’s a couple ways to physically link the two boards. One’s quite tidy, the other may be easier with stuff you already have around.

This 4-pin JST STEMMA cable connects between the I2C sockets on both HalloWing boards. Click, click, done!


If you go this route, both boards will share one power source…you only need a battery or USB cable to ONE of the HalloWing boards, the other will receive power through the STEMMA cable. In fact, use of two batteries is a bad idea in this setup, since they would be connected and the voltages may be slightly different.


But two boards means half the runtime from the single battery…you may want to switch to something bigger than the 400 mAh battery included in Adabox 009, if that’s what you’ve got. Or leave off the battery and use a USB cable to connect one of the HalloWings to a USB battery bank, the kind used for charging phones. That should run for hours!

The alternative is to use a few jumper wires to connect the two boards. These can be inserted into the FeatherWing socket pins on the back of the board.

Connect the same pins across both boards:

  • GND (there are two GND pins, either one will work)
  • SDA
  • SCL

Connect SDA on one board to SDA on the other board, SCL to SCL and so forth. You should not cross the wires; this is not a “null modem” connection.

Wired this way, each board can safely use its own separate battery. But if you’d prefer a single power source as with the STEMMA cable technique mentioned above, add one more jumper wire between the two boards:

  • BAT

Do NOT make this connection if using two batteries!

Remember with the single-battery approach that run time is halved. Consider using a USB power bank!

One More Jumper

NOW: in either case, whether using the STEMMA cable or jumper wires, ONE of the two HalloWing boards needs to control the show (while the other follows along).

Connect a jumper wire between a GND pin (there are two, use either one) and A2. Do this on only one of the boards. This one will now track the other when both are switched on.

In the diagrams above, we’ve added the wire to the left board (it’s highlighted in yellow)…but it can go on either one. But not both!

This guide was first published on Oct 26, 2018. It was last updated on Mar 08, 2024.

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

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