RFID Door Lock

Why I built it

I wanted to open my room with a card instead of a key, and to learn how real hardware is designed, not just wired on a breadboard. The lock is the first piece of a bigger Smart Room project, where lights and sensors will all report to one dashboard.

How it works

Tapping a card sends its ID from the MFRC522 reader to the ESP32. If the card is enrolled, the ESP32 switches a MOSFET that powers an electric strike: the door opens for a few seconds, then locks again. A green light and a short beep mean yes; red and a low beep mean no.

Up to 20 cards are stored in flash memory, so they survive a power cut. Five wrong cards within 30 seconds lock the reader for a minute.

Managing cards without a laptop

The admin card has hidden gestures. Tap it twice and the lock enters add mode: the next card you tap is enrolled. Tap it three times for remove mode. If nothing happens within 10 seconds, it goes back to normal.

The same controls are in a phone app built on Blynk, plus a few extras: approving the last card that was denied without walking to the door, a live temperature reading, and a log of every unlock.

The circuit board

I designed the board in KiCad, from the schematic to the layout, including a few custom footprints. It replaces the breadboard prototype and adds the protection a real installation needs:

• A fuse, reverse-polarity protection and a surge diode on the 12 V input
• A separate, clean 3.3 V supply just for the card reader
• A sense circuit that checks whether the strike really got power, so a broken wire shows up as a failure instead of a false success
• Fail-secure wiring: without power the door stays locked, while the inside handle always opens by hand

Red alerts

The board checks the Home Front Command alert feed every 5 seconds. When an alert covers the configured area, the door unlocks for 15 seconds, so nobody fumbles with a card on the way to the shelter. It triggers only once per alert wave.

What's next

The board is going to production. After that: Home Assistant on a Raspberry Pi and a wall touchscreen that controls the whole room.

What it does

• Custom 2-layer PCB designed in KiCad, 110 by 80 mm
• Drives a real electric strike, and stays locked if the power fails
• An admin card adds or removes other cards, no laptop needed
• Remote unlock and an event log from a phone app, plus over-the-air updates
• Unlocks automatically during Home Front Command alerts for the area

Built with

• ESP32
• C++
• KiCad
• Blynk