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RFID Detector for 13.56 MHz

Spot RFID tag transmitters from a distance

RFID Detector for 13.56 MHz

As we all know, checkout gates in highstreet stores will faithfully sound an alarm if you walk out with an item not ‘cleared’ by checkout staff, i.e., paid for. This article describes a sensitive detector that will equally faithfully produce a sound in response to pulses picked up from an 13.56 MHz RFID tag transmitter, be it large or small, ‘portal’ or ‘portable’.
The system of passive RFID recognition has been in use for decades already mainly in large department and fashion stores like C&A. Traditionally, these systems work at frequencies designated for ISM (industrial, scientific, medical) use.

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On the PCB copper track layout, all three pins of preset P1 are connected to ground instead of just two. The problem is easy to solve: the copper pad of P1 connected to pin 7 of IC1 (at the edge of the board, near the ‘Elektor’ print) has to be disconnected from the ground plane by cutting the three thin tracks between the pad and the ground plane.
Resistors:
R1 = 10kOhm
R2 = 8kOhm2
R3 = 2kOhm2
R4 = 470Ohm
R5 = 1kOhm5
R6 = 15kOhmOhm
R7 = 4k7
R8 = 100kOhm
R9 = 560Ohm
P1 = 100kOhm preset
Capacitors:
C1 = determine experimentally; start without it
C2 = 470pF
C3, C7-C10 = 100nF SMD case 0805
C4 = 22µF 16V radial
C5 = 39pF
C6 = 56pF
C11 =470nF
C12 = 1µF 16V radial
C13 = 47nF
C14 = 2µF2 16V radial
Semiconductors:
D1 = LED, green, low current
D2 = LED, red, low current
T1 = BC547B
T2,T3,T4 = BC557B
IC1 = NE615N or SA615N (DIP20 case)
IC2 = LP2951CN (DIP8 case)
X1 = 8MHz quartz crystal
BZ1 = 6V DC (active) buzzer
FL1,FL2 = SFE5.5 IF ceramic filter
S1 = on/off switch, 1 contact; alternatively a pushbutton
Case: Hammond 1590B diecast
9V battery with clip-on leads
PCB, ref. 040299-1
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