ESP32 Power Input

The DevKit V1 board includes an AMS1117-3.3 LDO regulator, so the power path matters: you feed it 5 V and it produces 3.3 V.

The onboard regulator

The AMS1117 takes 5 V (from USB VBUS or the 5V pin) and outputs a clean 3.3 V rail. The radio, OLED, GPS, and logic all run from this rail.

• Input range: roughly 4.5-7 V (5 V nominal).
• Output: 3.3 V at up to 800 mA (derated with heat).
• The beacon’s radio PA can draw bursts that the regulator handles easily.

Powering from USB

Plug the data cable into the board’s USB port. The AMS1117 regulates VBUS to 3.3 V. This is the standard bench configuration.

Powering from the battery

The battery path in this design is: 18650 → TP4056 → BAT+ → 5V/VBUS pin on the DevKit (through the AMS1117) → 3.3 V.

This works because the TP4056 BAT+ sits at 3.7-4.2 V, which is below the 5 V nominal but within the AMS1117’s dropout tolerance in practice. The 3.3 V rail remains valid down to about 3.7 V on BAT+, which matches the cell’s working range.

What not to do

• Do not feed 5 V directly into the 3V3 pin. The AMS1117 output is not designed to be driven and the ESP32 is not 5 V tolerant on power.
• Do not connect a cell to both the TP4056 input and the ESP32 5V pin without the module between them.
• Do not run the radio from the 3.3 V regulator if you measure sag below 3.2 V during TX: check the cell or the input wiring.

Measuring

• 3V3 to GND: 3.3 V.
• BAT+ to GND: 3.7-4.2 V depending on cell state.
• During TX the 3V3 rail should not sag more than ~0.1 V.