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DiscoverCircuits.com -- Hobby Corner
Last Updated on:
Monday, March 26, 2012 07:29 PM
Hobby Circuits'
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More
Indicator Circuits
Automotive Circuits
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125KHz Wireless Smart Key
Detector |
The hobby circuit below was designed to indicate if a key held over the small
coil of wire contains a 125KHz RFID chip. These chips are often used in smart car
ignition keys. The left side circuit forms a 125KHz power oscillator, which
drives the 680uH air core inductor. The magnetic field generated excites the
RFID chip inside the key. The AM signal produced by the key is stripped off of
the 125KHz carrier, is filtered and is routed to the clock input of a flip/flop. The
flip/flop is configured as a one-shot pulse generator. With the component
values shown, the clock signal only has to be about 100 millivolts peak to peak to
toggle the one-shot action. If the flip/flop is toggled, a red LED is turned
on. Try about 250 turns of 30 gage magnet wire with a diameter of one inch for the
air core coil. Tune the electronic circuit for 125KHz by adjusting the value
of the series 0.002uF cap.
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Click on Drawing Below to view PDF version of Schematic |
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