It turns out that hacking together a security keypad is remarkably simple if you know what you’re doing. [Don] needed to add a keypad with an RFID reader on it. He had previously built a USB RFID reader and thought he could integrate those concepts into the new unit.
He once again started with a serial to USB converter and removed the voltage converter IC for later use since he doesn’t need TTL levels for this project. The keypad is a USB product and it turns out there’s a hub inside. With plenty of space inside for the serial converter PCB and a blank spot at the top where he mounted the RFID reader, he adding a few passive components to wire it up and connect it to the hub. The only connection is the original USB cord but the PC will detect both the keypad and the converter.