Compact 45 mm x 35 mm 4-layer agricultural IoT sensor node using an ATmega4808, AMS1117-3.3 linear regulation from 12 V input, RS-485 Modbus RTU half-duplex, local I2C sensors, 0.96 inch OLED, status LED, and a 12 V solenoid valve driver with top-side sensors/display and bottom-side MCU/power partitioning.