Power on the expansion base
The expansion base makes no power. Every 3V3, 5V and ground hole on its strips is a pin of the ESP32-S3 carried out by copper: 3V3 at both ends of every strip, 5V on the right strips only, ground on both edges.
Where the holes come from
The base has no regulator, no battery connector and no power input. It is powered through the ESP32-S3's USB sockets, and every power hole on its strips is one of that board's pins, carried out by copper:
- 3V3, at both ends of all four strips. The output of the regulator on the ESP32-S3, which also feeds contact 2 of the display connector.
- 5V, on the right strips only, at the second and second-last holes. The board's 5V pin, which sits on its left row and is carried across the base.
- GND, two holes on each left strip and four on each right strip, all one net with the board's ground pins and the display connector's contact 1.
Nothing is switched, fused or filtered on the way. A short on a strip is a short on the ESP32-S3's own rail.
What the 5V hole reads
With a USB cable in, about 4.6 V: the cable's 5 V behind the diode the ESP32-S3 puts between its sockets and its 5V pin. That is plenty for anything rated for 5 V, and it is not regulated, so it moves with the port.
With no cable it reads nothing. If you power the board from a 3V3 hole instead, the 5V holes stay empty: the regulator only steps down.
The radio's burst
The ESP32-S3's datasheet gives about 340 mA at the peak while Wi-Fi transmits, and a USB port is meant to supply 500 mA in all. The burst lasts a moment and the rail dips with it. A sensor on a 3V3 hole sees that dip, and a sensor that resets when Wi-Fi connects is usually seeing it.
Put a capacitor of about 100 uF between 3V3 and ground, close to the sensor. It holds the rail up for the length of the burst. The base has none of its own, because it has no power parts at all.
What to take from which hole
Small sensors and a display: 3V3 and ground from the strip. That is what the holes are for.
Motors, relays, servos and long LED strips: their own supply, with its ground joined to a GND hole, because the regulator is small and is also running your sketch. No current rating for the strips or the sockets is quoted here, because none has been checked.
When it does not work
It is the ESP32-S3's 5V pin, which sits behind a Schottky diode from the USB sockets. The diode costs three or four tenths of a volt. Nothing is wrong, and anything rated for 5 V runs from it.
With no USB cable in, the 5V holes only have voltage if you feed them. Powering the board through a 3V3 hole leaves 5V empty, because the regulator only passes current from 5 V down to 3.3 V, not back up.
The radio draws a burst of a few hundred milliamps as it transmits, and a load on the same rail makes the dip deeper. Add a 100 uF capacitor between 3V3 and GND close to the sensor, turn the transmit power down, or give the load its own supply.
They are drawing from a regulator that is also running the chip. Give them their own supply and join its ground to one of the base's GND holes. Do not power them from a 3V3 or 5V hole.
An LED and a button on two jumper wires, and a sketch that uses both.
A first build on the expansion base →Edit this page — content/books/esp32s3-base/expansion-power.mdx
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