I was wondering if there were any tags available that could sense an external electronic circuit as being "on" or "off"—to determine, for example, whether or not a red street signal light was lit—and then transmit a readable signal to an RFID reader accordingly.
—M. Amiruzzaman (Kuala Lumpur)
Dear M. Amiruzzaman,
There are passive and active tags that have input/output (I/O) ports that would enable you to connect an external electrical circuit. Passive ultrahigh-frequency (UHF) chips with I/O ports are available from Intelleflex, NXP Semiconductors, Tego and EM Microelectronic.
Most active tags allow you to attach sensors, so you could create a circuit that would indicate whether a light was on or off. Which option you should choose would depend on the read range involved for your particular application. A passive UHF tag can be read from around 20 feet to 30 feet away, while an active tag can be interrogated from a distance of 1,000 feet or more.
—Mark Roberti, Founder and Editor, RFID Journal
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