There's a special version of the remapper that takes inputs from a serial mouse and translates them to USB. It's different from most adapters in that they usually only convert RS-232 to USB serial. This converts to USB HID and you can use it even if your operating system doesn't support serial mice at all. The remapping functionality works as usual (there's no polling rate overclocking). Currently only the Microsoft serial mouse protocol is supported.
You can either use the RP2040-RS232 adapter or you can make your own as described below. If you use the RP2040-RS232 adapter, the multi-firmware that comes with it includes the serial variant of HID Remapper. You can also just use the firmware linked here if you want.
To make one yourself you will need a Raspberry Pi Pico, a Pololu 23201a Serial Adapter, and also a null modem adapter and a DB9 gender changer (on the photo below these are two separate adapters, but you can also get one that does both).
The provided remapper_serial.uf2 file can be used to flash the firmware onto the Pico the usual way (hold BOOTSEL button while connecting to the computer, then copy the UF2 file to the USB drive that shows up).
The pin connections are as follows:
| Pico | serial adapter |
|---|---|
| 3V3 (pin 36) | VCC |
| 3V3 (pin 36) | RX |
| GND (pin 38) | GND |
| GND (pin 38) | DSR |
| GND (pin 38) | CTS |
| GPIO21 (pin 27) | TX |