Treasure Chest using Relays

There exist special types of relay that have peculiar characteristics. Next to the ‘normal’ types in the catalogue we find the so-called ‘latching’ types which have two stable states. There are two types of latching relay, with either one or two coils. Types with just one coil are reset by applying a reversepolarity voltage to the coil, while those with two coils are reset by applying a voltage (of the same polarity) to the second coil. It is the version with two coils that we will use in this circuit.