RFID Card Reader with PIC Applied

Figure 1 

The project utilizes a PIC16F628A with an on-chip comparator in order to feed the output from the op-amp directly into the PIC and extract the digital signal from an RFID card reader.

The use of PIC16F628A is for more efficient signal reading by using interrupt based compare capture module since it is provides 150kHz carrier signal generation. Changing the values of capacitance causes the frequency of the entire system to be fine tuned. This is made possible using the function generator to sweep for the peak output observed with the scope where the capacitor size is altered until the peak response of the resonance circuit is at 150kHz.

The op-amp used in the project is TL062 with a simple diode detector. The detected voltage goes through the first op-amp configured as an inverting amplifier with low pass frequency response which will remove bulk of the carrier frequency. Extracting the FSK signal is the next stage of analog circuit which is a resonant band pass circuit with a center frequency.

The capture hardware shares resources with the PWM module that generates the 150kHz carrier signal, and only one function activates at a time.

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