When using bipolar transistors for switching you do not use the current gain (beta) to determine appropriate base current. That parameter is specified when the transistor is in its linear region with a significant Vce. Gain drops off dramatically as Vce falls. The normal 'rule' for switching is that...

Using a bipolar transistor like a 2n2222 is not a great idea for switching the current to the solenoid. For a 300mA solenoid you would need to feed about 30mA into the base of the transistor to saturate it (switch it hard on). That is to much for a GPIO pin. You could use a darlington transistor lik...

As has been pointed out a series gate resistor does very little when using a MOSFET driver. The only possible benefit would be to add a degree of protection to the GPIO pin if there was some catastrophic failure in the MOSFET device. These tend to be very reliable devices and I do not add a series r...

You can use the TXD and RXD pins as GPIO.

Obviously they are not operational during a flash upload operation which may mean swapping wires to do uploads but if you use OTA then that doesn't matter after the first flash.

Using RXD doesn't affect any serial debug print but using TXD will.

If you use an esp32 module with 4MByte PSRAM (e.g. WROVER) then you can store your whole capture in a buffer before writing out to file.

I don't know why GPIO14 would affect the boot unless it is something to do with the camera software. Maybe try it with a minimal sketch to see if that boots OK with GPIO14 pulled up. On my camera app I do use the SD card so there is little IO free. I use RXD as GPIO3 pin; just use pinMode in setup.....

Everything on the board runs from the 3.3V rail. There are 2.8V and 1.2V rails but these are derived from the 3.3V rail. The only thing the 5V connection does is connect to a 1117 linear regulator to provide the 3.3V. So if the board works fine when fed directly from 3.3V then there seems to be only...

5V power banks contain a LIPO battery, a boost circuit to generate +5V out normally via a USB A socket, and a charger circuit typically with a micro USB input. They are available in various capacities from 2500maH upwards. So you can connect a standard phone type charger into the micro socket for ch...

I don't know about this board but many dev boards put a series resistor between the TX of the bridge and the cpu RX. This allows an external signal to override it without causing a conflict. The TX from the cpu to the RX of the bridge is not a problem. The resistor used can be quite low (e.g. 470 Oh...