vvstubbs / latchrelay

An Arduino library to control dual-coil latching relays.

LatchRelay

This Arduino library is intended for the EC2-5TNU and similar dual-coil latching relays. It encapsulates the pulse generation necessary to flip the state of the relay, and allows that state to be polled.

Use in code

Object creation

This library defines the class LatchRelay to drive the switch. The constructor has the form

LatchRelay(onPin, offPin);

where onPin and offPin are of type byte and indicate the pins used to control the relay. onPin is the pin that pulses high to switch the relay on, while offPin is the pin to pulse high to switch off.

Initialization

If relay is an object of type LatchRelay, then somewhere during setup the init() method should be called:

relay.init();

This declares the pins named in the constructor as outputs, without changing the switch state. If a default starting state is desired, pass a boolean to the function to force it to start on or off:

relay.init(0); //start off
relay.init(1); //start on

Controlling the Relay

The relay is controlled via the setState() function, which takes a boolean argument:

relay.setState(0); //set to off
relay.setState(1); //set to on

Alternatively, use actual bool expressions - these are equivalent (though wordier)

relay.setState(false); //set to off
relay.setState(true); //set to on

Whenever this function is called, the object tracks the relay state, which can be polled:

bool relayState = relay.getState();

There is no explicit function to toggle the switch state, but this is easy enough by combining the get and set methods:

relay.setState(!relay.getState());

Note that getState() only tracks the value passed to the last call to setState() and cannot actually poll the physical state of the switch. Thus, it is possible (though unlikely) that the switch fails to change but getState() would not reflect this. If this occurs regularly, external verification should be used. Additionally, if the init() function with no paramaters is called, the object has no way of knowing the current switch state, and getState() will default to reporting as off until the state is set for the first time.

Naming Convention

Although the library naming convention assumes the user is toggling a switch on and off, the physical relay actually toggles which of two pins a third pin is connected to. Thus, the user could route a signal in either of two ways, both of which would be a form of "on". In this case, 0 and 1 simply represent these two different states of the relay, with onPin and offPin being the pins used to set the relay to states 1 and 0, respectively.