I have experience with ESP32 Dev board but this is first time with custom PCB.
I connected RX-TX, TX-RX. ESP32 got 3.3V stable. boot-press-hold-reset-press-release.
But I got Invalid head of packet or No serial data received.
Is it problem with the schematic or PCB layout? How can I fix / debug this?
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Best Answer
It looks like the EN line is missing a pull-up.
The principle is that it should be pulled high for normal operation, and pulled low (via the reset button) for reset.
The resistor is visible as R1 on page 24 of the ESP32-PICO-MINI-02 datasheet, or as R11 on the schematic you linked to in comments, which is for different models of the ESP32 modules.
Also, unrelated: you should read Espressif's Hardware Design Guidelines, especially section 3.1.2. I don't think the module's antenna over a ground plane (or whatever all that copper is on the part of the PCB beyond the gap) is a good idea. The PCB Design and Module placement guide has more information on the topic. Basically you should never have any copper trace under the antenna, and maintain a clearance around it.