Last two days I played with the ESP01. I got it working and it is able to replace the serial USB cable connection. The ESP01 Rx/Tx is connected to the Pico's console port pins like the UART converter.
The traffic is transmitted through Wifi and the protocol is Telnet (RFC2217).
On Linux I found two programs to create a virtual serial device like /dev/ttyPico0 where the telnet traffic is bridged to. This interface can be accessed by programs in the same way than with the USB UART converter.
The ESP01 can be an access point or a station. If it is used as access point it acts as a hub and two clients logged in via Wifi can talk to each other via TCP/IP. So if the RM2 of the PC3 is used it can connect to the ESP01 as well and can be reached through a connected PC.
The ESP01 is flashed with the ESP-Link software and on Linux the virtual serial port and the bridging can be done with socat or with ttynvt

I found one problem with the original ESP-Link software. The serial timeout is set to 5 minutes in the official binary firmware. If a terminal like Putty is open and no traffic goes through then Putty will close after 5 minutes.
I changed that in the source and recompiled the firmware. As ESP-Link is old and not maintained anymore, I used this fork which also puts in some fixes and small changes to the Makefile and python scripts that it compiles on actual distros.

A switch to power the module and the other to change Rx/Tx between UART converter and ESP01:  

Final pictures:




I bought a second Pimoroni RM2 but still get these errors with WebMiteRP2350V7.0.00b4
I will once more check the cables and and will test with a second PGA2350.

But on PicoMiteHDMIWEBV7.0.00b4 the module runs without problems and real good Wifi speed!

Hi dddns,

Note that on the 3.1 and 3.2 revision of the PC3, there is GP20/GP21 (system I2C) on 2 of the 4 pins +5V/GND. If you desire 100% compatibility.
System I2C is useful if you need to a connect WII/Nunchuck controller.

Volhout
Edited 2026-10-05 21:05 by Volhout

Please try option cpuspeed 315000 and see if that works with the webmite firmware. At the default the cyw43 spi is running at the maximum rated speed of 50MHz. At 315MHz cpu speed it runs at 39.4MHz and at 252MHz it is 42MHz. Obviously the spi wiring to the module should be kept as short and tidy as possible.
I notice that the Pimoroni breakout has no capacitors. The PC3 uses two 100nF caps close to the VDDIO and VIN pins on the board. Both firmware versions work perfectly on the PC3.
Edited 2026-10-05 21:08 by matherp

  Volhout said  

Hi dddns,

Note that on the 3.1 and 3.2 revision of the PC3, there is GP20/GP21 (system I2C) on 2 of the 4 pins +5V/GND. If you desire 100% compatibility.
System I2C is useful if you need to a connect WII/Nunchuck controller.

Volhout

I missed that.. But I have System I2C on the 4 pin header left to the DS3231

  matherp said  

Please try option cpuspeed 315000 and see if that works with the webmite firmware. At the default the cyw43 spi is running at the maximum rated speed of 50MHz. At 315MHz cpu speed it runs at 39.4MHz and at 252MHz it is 42MHz. Obviously the spi wiring to the module should be kept as short and tidy as possible.
I notice that the Pimoroni breakout has no capacitors. The PC3 uses two 100nF caps close to the VDDIO and VIN pins on the board. Both firmware versions work perfectly on the PC3.

Thank you! I will report.
I added a 100nF to Vin but not VDDIO. That sounds promising but needs to be soldered to the RM2 itself. Will try that on the first module I bought as it is already re-soldered.