This AX22-sized board drops a Hongfa HK4100F-DC3V-SHG mechanical relay onto a 22 × 22 mm PCB, letting you switch mains-level or high-current loads with a single microcontroller pin. An onboard N-channel transistor driver, fly-back diode, and status LED handle the 3 V coil’s ~90 mA draw and protect your logic lines. Snap it into any AX22
