The screw terminal base

Wiring that stays put

The ESP32-C3 OLED board seats in two 8-way sockets down the middle. Beside them, a block of eight screw terminals runs down each long edge at a 3.5 mm pitch, one terminal for each of the board's sixteen holes. This is the base for wiring that will be carried, driven somewhere or left alone: there is nothing to solder, and nothing between a terminal and the board's hole.

The wire goes into the clamp and the screw closes it. A screw that has closed on insulation feels tight and tests dead, so back it out until you can see the clamp open, put bare copper under it, and tighten until the wire will not pull out by hand.

Which terminal is which

Tap a terminal, or pick a GPIO, and the figure says where it is and whether the board already has a use for it.

The label printed beside a terminal is the label printed beside the board's own hole, so nothing here is renumbered. TX is GPIO 21 and RX is GPIO 20, and the terminals printed 3V and 5V are the 3.3 V and the USB 5 V. The two blocks are wired straight to the two sockets, and the net list has no part between a terminal and its hole.

The base's own numbering is the other way up. The right block is a part numbered from the bottom: its way 1 is 5V and its way 8 is GPIO 0. Nothing you wire depends on it, and the silkscreen is the thing to read.

The power is on one side

The right block carries 3V, GND and 5V, one terminal each. The left block carries none: it is GPIO 3 to 10 and nothing else. That is the thing people get wrong, because a block of eight terminals looks like a header, and a header usually has a ground in it.

So a module on the left block takes its supply from the right: a wire from the 3V terminal across the board, and another from GND. There is also only one GND terminal and one 3V. A project with several modules is easier with a small breadboard or terminal strip that carries the ground and supply, with a single wire from each terminal to it.

Six holes already have a job

GPIO 5 and 6 are the display's bus, GPIO 8 is the blue LED, GPIO 9 is the BOO button, and GPIO 20 and 21 are the serial port. All six are terminals, and a wire on one is on the board's own part too. The sixteen pins says what each costs you. GPIO 2 is free as shipped, and stops being free if the BATTERY MONITOR jumper is bridged.

Size and mounting

The base is 44.5 mm long and 32.5 mm wide, from its mechanical drawing, and its tallest part is a terminal block, 8.7 mm above the board (10.3 mm from the underside, where the terminals' legs stand 1.9 mm proud). There are two mounting holes, 4.8 mm across and 16 mm apart, near the switch end.

The back of the base prints the settings the board needs: the LED on IO8, RX on IO20 and TX on IO21, the display's controller and address, SDA on IO5 and SCL on IO6, and the line Wire.begin(5,6). It also prints WIFI_POWER_15DBM TO 8_5DBM, which is the Wi-Fi article's advice to turn the transmit power down.