Wiring and parts

Parts

You need an ESP32-WROOM-32 DevKit V1 (the 30-pin and 38-pin versions both work), a 0.96 inch SSD1306 OLED (128 by 64, I2C), and a UART barcode module such as the GM66 or the Waveshare scanner.

For feedback, add one green and one red 5 mm LED and an active piezo buzzer. The lock is driven by a 5 V single-channel relay module with an optocoupler, which switches the solenoid or turnstile. The manual override is an ordinary push button plus a 10 kΩ resistor. A 5 V 2 A supply powers the lot.

Pinout

Part	GPIO	Notes
OLED SDA	21	I2C data, 3.3 V
OLED SCL	22	I2C clock, 3.3 V
Green LED	18	High = on
Red LED	19	High = on
Buzzer	23	PWM. 2400 Hz for success, 450 Hz for alerts
Gate relay	27	High = open. 3 second pulse
Scanner, into the ESP32	16 (RX2)	From the scanner’s TX
Scanner, out of the ESP32	17 (TX2)	Configuration commands
Override button	34	Low = pressed. Needs the external pull-up

Danger

GPIO 34 has no internal pull-up resistor. Wire the 10 kΩ resistor from GPIO 34 to 3.3 V. Without it the pin floats and the gate can open on its own.

The diagram above is docs/circuit_diagram.svg from the hardware repository.