This Smart Dual Coil latching Relay board can control the ON/OFF power of a device by applying a short voltage pulse to input 1 and input 2. This project is useful in low power applications since the coil is not powered all the time and only requires a short voltage pulse. The relay coil remains in that position even if the power is disconnected. The project is built using FAN3240 chips from ONSEMI. This chip includes dual high current relay drivers designed to drive dual-coil polarized latching relays that connect and disconnect power in smart electronic meters and solar inverter applications. The IC includes auto thermal shutdown and a filter/timer block is there to prevent inadvertent switching from noisy input signals by providing input-pulse qualification (tQUAL) and maximum output pulse width limit (tMAX). Polarized, bi-stable, latching relays are utilized in many kinds of electronics equipment and diverse applications. These relays usually employ two coils, one to move the relay contacts(s) from open to close position and another coil to move the contacts(s) from close to open position. To facilitate mechanical movement, the relay coils need to be energized for a specific time interval. Once the contact(s) have changed position, the voltage should be removed from the winding of the relay. As shown in the schematic below, a dual-coil relay is connected to its supply rail at the center point of the two relay windings. Each winding can be energized by the switches connected to the relay coils out-1 and output-2. Diodes D4 and D5 are used as clamping diodes. Operation is very simple, enable PINs need to be high, apply minimum 15ms trigger voltage to input 1, this will provide 150ms pulse to relay coil -1 and coil moves contact(s) open to close, and when 15ms pulse is applied to input 2, coil-2 energized for 150ms and moves the contact(s) from close to open. Capacitor C3 is a filter capacitor for the internal 5V regulator of the chip.