m68hc08 serial programmer schematic design

So you would do this: 12VDC -> 5V Switching PSU ->3.3V LDO, use the 5V for the solenoid coil only, and for 3.3V LDO. The size of this is smaller than the size of the WROVER module, so very tiny, but can output 2A-s easily. The underside of the PCB is flat, so you can just solder it onto your PCB as a module, and adjust the output as needed. Intead of the LDO, use a DC-DC buck converter like this one. Consider that when using Wifi, the ESP32 can momentarily have 400mA spikes, and the coil probably consumes some 5V power also, this would require you to have good heat dissipation for the 5V LDO, which is a pain in the ass, to design. Your solenoid will for sure burn down the LDO when engaged. Rather, connect an 10K between the gate and the ground to make sure the gate has a defined level even when the GPIO is tristated. I think you're confusing the topology for one you'd use with a BJT, for a mosfet this is unnecesary. Your mosfet has an unneeded gate resistor (R4) in its signal path. Watch their output current, though, make sure it's >=500mA max) For instance, the HLK-PM01 would work really well here (but there also are other integrated 5V switch converters that can work. In general, why not use a 5V PSU? I don't see the 12V being used for anything but the LDOs. I assume the TRANSFO_12V block actually is a transformer plus bridge rectifier plus smoothing caps, or actually a switched mode power supply in any case, something that spits out a reasonably smooth 12VDC and not AC? If not, you should add a bridge rectifier and some hefty electrolythics.

This way, the power dissipation resulting form the voltage drop between the 12V and 3.3V line is shared between the two LDOs. Makes it easier to automatically flash your board (resetting and putting it in boot mode using handshake pins on your USB-to-serial-converter), making development less painful. I'd put the reset, GPIO0, TxD, RxD and Gnd on one connector. For instance, it suggests a slightly more complex reset circuit consisting of a RC-combination.

In general, check the hardware design guidelines for what applies to your situation.

M68hc08 serial programmer schematic design