Headers on, and which way round

Headers first

Each board takes two of the strips, one down each row. The pins go in from the underside, so the long ends point away from the parts and the labels stay on top where you can read them.

The easy way to get them straight is to let a shield hold them:

1. Push both strips, long ends down, into the shield's two inner socket rows.
2. Lay the board over them, parts up, antenna at the switch end.
3. Solder one pin at each end of each row, and check that the board sits flat.
4. Solder the rest, then lift the board out with the strips attached.

Twenty-six joints, each one a cone of shiny solder around the pin. A joint that looks like a grey ball is not holding, and a joint that joins its neighbour is a short — cold joints and bridges has pictures of both.

Which way round

The shield has the switch at one end and USB printed at the other. The board has its antenna at one end and USB-C at the other. They go together the obvious way: antenna over the switch, USB-C over the word USB.

Why turned round is not just the wrong labels

Both rows are thirteen holes long, so the board fits in either way. Turned round, every pin is in the wrong socket, and three of them matter:

• The board's 3V pin sits in the shield's GND socket.
• The board's G pin sits in the shield's 3V socket.
• The shield's 36 socket, where the battery monitor lands, holds the board's GPIO 13.

The shield's ground is the cell's negative, and the TO ESP32 cable joins that to the board's own ground. So with the cable connected, the regulator's 3.3 V output is shorted to ground through the shield. Check both ends before the cell goes in, every time you seat a board.

Then the cable

With the board seated, run one of the six cables from the shield's TO ESP32 socket to the board's own battery socket, red wire to the + mark at each end. That cable is the only way the cell reaches the board. The cell itself goes in LIPO BTT — which pin is plus before you do.