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Its difficult to comment anything on this circuit unless we know
what program is there in PIC processor??
IC 74HC4060 is used here to generate clock and driving voltage for
coil L2 acting as antenna.
IC 74HCT04 not gates are used to boost the output current from 4060
clock generator timer.
R7 L1 and C5 form a series resonator circuit o/p of which is a sine wave
fed to power amplifier (formed by VT1, VT2, VT3) which drives the antenna
coil L2.
L2 and C10 form a kind of voltage divider.
Diode VD4 R11 R13 and C8 C9 network form a rectifier filter circuit (detector cicuit).
O/p form rectifier and filter circuit is fed to op-amp DA2:C which is acting as
an high gain inverting amplifier with limiter.
DA2:B is acting as another high gain inverting amplifier.
DA2:A is acting as a schimmit trigger.
Need to know more about the L & C circuit shown in right corner.
This circuit might be affecting the value of L2 (antenna)
This as an anti-theft alarm device as the ones installed at the doors of shops.
The transmitter transmits 125kHz signal, which picked up by the right hand dongle (attached to the good) that has a resonant circuit at 125kHz. this signal is rectified in the dongle and activates a digital chip that loads the 125kHz LC circuit with a long binary code (a "1" loads the LC circuit and the "0" does not). The varying loading is sensed as varying amplitude of the Tx signal across the transmit loop, rectified amplified and fed to the microprocessor that detects the binary code word, and sets on the alarm.
It is rfid transponder reader and i suppose link to the site was previously posted here (search for rfid) . Project was located on one of the russian sites .
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