RFID LF (100-150khz) support

[Britaliope]

Hello,

I'm currently looking into this project, and it seems very intresting, however i'd like to have RFID LF support (especially for reading animal chips that are 134.2khz). I'm currently looking for suitable modules at a decent price that could be integrated on this, and if I manage to find something useful, i'll submit a PR with my modifications.

I am opening this issue to track progress. Also, if anyone already made some research about this i'd be happy to hear what you found and thoughts. @controlpaths , as you designed the board : do you have any insights or advice, or things to be careful about while choosing and modifying the kicad project ?

From what i saw, there are some GPIO pins available on the RP2040, so a UART module would be OK, but a I2C or SPI one would do too. I noted that both UART from the rp2040 are used (for external USB & esp com for wifi), but from what I understand, that would mean that we can use at most two of those three features at the same times, which is not that a big limit imho : use cases where wifi, external USB as well as lf rfid are used at the same time doesn't seem likely.

[controlpaths]

Hi! The problem with low frequencies is that the antenna is bigger than for hundreds of MHz. I don't know modules for that frequency, but if you find it, it will need a PCB antenna.