Minimal Hardware to program Lopy4 with USB

[ProtonX]

Hi
I would like to build a custom PCB that connects to the Lopy4. Now I need some information about the minimal hardware I need to add a USB-Micro port. I have seen that Pycom uses a custom PIC16 on the Expansion Board V3 (Not very helpful in my case) and an FTDI-IC on the V2. So I guess what I need is the hardware path of the V2 from USB to RX0/TX0 (?).

Has someone already did this?
I would be very thankful for some help.

Kind regards
ProtonX

EDIT: Just to be clear... The USB port will only be used to program the lopy4.

[robert-hh]

@protonx I made myself a base board too for the Pycom modules. A Kicad sketch is here: https://github.com/robert-hh/Pycom-baseboard
It uses pre-built modules for USB/Serial and SD card. I did not want to deal with SMD parts, and space did not matter. It also has the espressif logic for activating the bootloader, and jumpers for the connection to Reset, Tx, Rx and P2.
Not that this costs less than an Pycom expansion board, but it makes fewer troubles when using (no PIC, standard drivers, ..)

[John Baird]

@protonx Hi. When I first started working with Pycom modules I didn’t have a Pycom board for them, so I placed them in a bread board and used a USB to 3.3v TTL converter (similar to this TTL Cable). All I connected was GND / TX / RX and it worked like a charm.

If you want to make a minimal PCB you might consider keeping the USB interface seperate and just provide a header that cables like this to connect to. Doing so means the modules pretty much stand alone.

(Note that for flashing new firmware you need to apply a jumper to a particular pin. I just did this with a wire link. You could run that pin to the header as well for ease of use)