JUL30

Lazy man's USB RFID reader

When we want to connect our RFID reader IC to PC it would be great if it could be powered by and connected to USB port. To avoid building our serial to usb converter we can simply purchase one from a local PC store. In that case we need UART-TTL voltage converter.

RFID reader modules that we can purchase usually work with TTL voltage levels and are powered from 5V. As the serial to usb converter module offers "real" UART port with UART voltages, we also need MAX232 to make it compatible with our 5V reader. This can be done a bit differently but it involves opening and hacking into a serial to usb converter. Read on to see how it can be done to save some money and get an extra IC!

First step would be to pry open the serial to usb converter. This can be done with a scalpel or a saw to get things started. After that we can desolder the existing TTL-UART voltage converter that is usually MAX213. We can skip this step if we don't want this extra IC in our parts box. We also don't need the cable with DB-9 connector anymore, so this can also go away.

After that we need to drill some holes for our RFID reader IC. In this case we are using ID-12 125kHz reader.

Next thing would be to detect the RX pin of usb-serial converter which is in most cases Prolific PL2303.

On it's pin 5 we need to connect the "Data out" pin of RFID reader. Besides that we also need to connect the GND pins of both chips together (usually black wire) and we need to supply +5V to our RFID reader from the USB port (usually red wire). Please see schematics below for more information.

LED can be connected to RFID reader that will blink whenever a card is read. This LED can be used to fill the hole from the cable of DB-9 connector that we have also removed.

Schematics

Finished contraption

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