Although I was working with linear voltage regulators before (using AMS1117) - for USB use, I wanted to make another device that would work with 18650 LIPO battery, and would use 3.3V. And this device should have as less fragile components as possible. See discussion on stackexchange on choosing specific chip.

This is also my first experiment device with lipo protection - initially I was using FS312F-G, but it requires also external mosfet, has 6 pins and is much easier to mess up. (And also is external device, so costs money to assemble). I was vary happy with XB3303A chip that is tiny, has only 3 pins and does not require much external components.

What worked (or was tested)

• ESP-12F works! Blink is ok.
• Programming through Serial pins.
• 3.3V converter does work, shifting voltage to 3.3V.
• Lipo Unvervoltage protection also works
• WS2812B socket and LED’s control
• Buttons
• ADC
• Flash pad

What does not work as expected:

• I’ve messed up PullUp/Pulldown for GPIO15 and GPIO00, so device failed to start for me. And I’ve ordered 30 pcbs to be assembled! So one reistor array should be desoldered and 3 resistors should be added.
• For some reason NPN transistor was placed incorrect - causing short circuit on the board. It took me 6 boards, desoldering components one-by-one to get it wright. So no buzzer this time.
• Flash pad has not the best location - I should point carefully with tweezers for it to work. Also it’s too big - i would need to find someting like 1.27mm.
• Buttons are too close to each other. I need some fancy case for them to work.
• LiPo undervoltage protection - not as expected - it kills voltage supply at around 2.5 volts. Hope that it would would not destroy 18650 batteries for me.
• LiPo battery reverse protection does not seem to work - it consumes around 1 amp of voltage and overheats.