An 11.0592MHz quartz crystal connected to pins 18 and 19 provides basic clock to the microcontroller. Power-on reset is provided by the combination of electrolytic capacitor C4 and resistor R1. Switch S1 is used for manual reset. Port pins 21 through Pin 28 of the microcontroller are connected to data port pins D0 through D7 of the LCD, respectively. Port pins Pin 17 and Pin 16 of the microcontroller are connected to register-select (RS) and enable (E) pins of the LCD, respectively. Pin no.5 of the LCD is grounded to enable for write operation.
All the data is sent to the LCD in ASCII format for display. Only the commands are sent in hex form. Register-select (RS) signal is used to distinguish between data (RS=1) and command (RS=0). Preset VR1 is used to control the contrast of the LCD. Resistor R6 limits the current through the backlight of the LCD. Port pin 10 and Pin 11 of the microcontroller are used to interface with the RFID reader.
When an authorised person having the tag enters the RF field generated by the RFID reader, RF signal is generated by the RFID reader to transmit energy to the tag and retrieve data from the tag. Then the RFID reader communicates through RXD and TXD pins of the microcontroller for further processing.
Thus on identifying the authorised person, port pin 12 goes high, transistor T2 drives into saturation, and relay RL1 energises to open the door for the person. Simultaneously, the LCD shows “access granted” message and port pin 8 drives piezobuzzer PZ1 via transistor T1 for aural indication.
If the person is unauthorised, the LCD shows “access denied” and the door doesn’t open. LED2 and LED3 show presence of the tag in the RFID reader’s electromagnetic field.
To derive the power supply, the 230V, 50Hz AC mains is stepped down by transformer X1 to deliver a secondary output of 15V, 500 mA. The transformer output is rectified by a full-wave rectifier comprising diodes D1 through D4, filtered by capacitor C1 and regulated by ICs 7812 (IC2) and 7805 (IC3). Capacitor C2 bypasses the ripples present in the regulated supply. LED1 acts as the power indicator and R2 limits the current through LED1.
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