smartRFID

As the first smart sensor, smartColours, is close to completion, I'm starting a new project called smartRFID.

RFID stands for Radio-Frequency IDentification (reference). RFID is used everywhere: price tags on the department stores, contact-less keys for cars, clocking cards at offices...

There are various kinds of RFID tags, with different operating frequencies —most common are 125 KHz or 13,56 MHz—, features —read-only or  write-and-read—, operating distance from which it can be read —from 1 cm up to 100 m— and formats —from very small as capsule, button, up to classic credit card form-factor. 

The RFID system consists on a reader and one or more tags. Both the reader and the tag are two-way radio transmitter-receivers. The reader sends a signal to the tag, and the tag sends its unique identifier back. The tag doesn't require a battery, as its antenna takes the energy from the radio waves and powers the micro-chip (reference).

The idea is to use RFID tags, for example to identify boxes.
Please note the RIFD readers used for the smartRFID module are deprecated and no longer available. 

Functional Description

The goal is to read RFID tags. 

I selected a basic RFID tag, read-only, which provides a unique combination of 5 bytes plus 1 byte for checksum validation. Five bytes —or 40 bits— provide 1 099 511 627 776 unique combinations!

As for the colours, reading any and all RFID tags is possible, but identifying the tags currently used seems more useful. Instead of a lengthy identification sequence, I prefer to deal with just a number. So the RFID unique combination with 5 bytes needs to be translated into a single digit number. This will be done by a table.

Operating distance should be consistent with the scale of fischertechnik models. An operating distance between 2 and 4 cm seems convenient.

The sensor would be connected through I²C to the Robo TX controller and should fit into a 30 x 30 x 30 yellow box (references 38287 and 38440).

Commands

There are only two main commands:
  • smRFID_begin initialises the sensor and returns an error if the sensor is not available.
  • smRFID_read reads the unique identifier of the RFID tag if one tag is available and proceeds to the checksum validation; returns an error if no tag is available or if the checksum is not valid.

The following commands provide a more advanced usage. Instead of dealing with a lengthy RFID unique identifier with 5 bytes, smRFID_identify read the 5 bytes RFID tag, controls the check-sum and returns a single digit number:
  • smRFID_identify reads the unique identifier of the RFID tag if one tag is available and provides the associated number; otherwise returns an error.
  • smRFID_translate translates the unique RFID identifier into a single digit number. This table is hard coded and edited on Robo Pro.
  • smRFID_test tests the connection.


The commands are detailed here.

Prototype

Contrary the the smartColours sensor, the RFID reader comes ready to use. 

Only a protocol adapter with logic level converter is required. So there's no need for a prototype!

Finalised and Working Sensor

The sensor fits into a 3 x 3 x 3 cm yellow box.

First tests allow the RFID tags to be read at 3 cm.

This is consistent with the scale of fischertechnik models.
Posted: 22 Oct 2011
Updated: 15 Jan 2020