I found this SeedStudio RFID reader which is listed as supporting 3.3v to 5v input. To use this with RPi, do I need to add logic level conversion / resistors or can I use it directly on a 5v pin? The reason for my question is that its big brother RDS630 requires resistors. Both product links included below:
mini rfid reader: Mini 125Khz RFID Module - Pre-Soldered Antenna (35mm Reading Distance) - Seeed Studio
RDS630: 125Khz RFID module - UART (Seeed Studio) | SS113990014 | Core Electronics Australia
In general, a device will not drive its logic pins higher than VCC (unless something has gone very wrong).
With this in mind, if you wanted to use those modules with a Raspberry Pi (a 3.3V device) I’d power the RFID board with 3.3V, and use it without logic level converters (they wouldn’t be needed).