Controllers

The three components, Sensors, Gateways, and Processors, can be considered to be the input side of an IoT solution. If the data is to be read, received, processed, stored, or displayed to humans for review and analysis, the IoT solution would be complete with these three components. However, IoT systems can do much more in terms of taking decisions and actual actions. The side that takes action can be considered to be the output side of the IoT solution.

A comprehensive IoT solution can work without any human intervention. It can not only read and analyse data from sensors but also uses that analysis to control other things and make them do something. A controller is a device or a system that is responsible for and capable of moving and controlling machines, which we refer to as Workers.

For example, when a car drives up to a gate, a sensor can detect the presence of the car and send a signal to a motor controlling the gate movement to open the gate. Or, a soil moisture sensor can detect that plants need watering and open a valve that releases the supply of water.

There are two common types of controllers used in IoT solutions: Actuators and Relays.

Actuators

An actuator is a component that is capable of moving and controlling a mechanism or system. It requires a control signal and a source of energy, generally electrical power, but could also be hydraulic power. The control signal is usually a low-energy electric voltage or current. When it receives a control signal, an actuator responds by converting the energy into mechanical motion.

Thus, digital or analog signals from processors, or even directly from sensors, can act as control signals for an actuator and change the state of the machine they are controlling.

Actuators generally provide controlled and limited movements or positioning. The two basic motions are linear and rotary. Linear actuators convert energy into straight-line motion, typically for positioning applications. They usually have a push and pull function. Rotary actuators convert energy to provide rotary motion. Each actuator type has versions for different power configurations and comes in many styles and sizes depending on the application.

One of the most common types of rotary actuators is the servomotor. While a motor rotates continuously and fully in one direction, a servomotor rotates in small increments in either direction depending on the control signal provided. For example, in an electric airplane, a motor will drive the propeller which rotates continuously in one direction. But a servomotor (acting as an actuator) will move the control surfaces (ailerons, rudder, and elevators) which need small, controlled movements in both directions.

Servomotors are also used in robots, to move parts of the robot in small movements in multiple directions.

This is a schematic of a linear actuator. When the electric current is passed through the coil it creates a magnetic field that pulls up the armature and the stem. When the current stops, the spring pushes the armature and stem back down.

Relays

A relay is an electronic or electromechanical switch that can open and close electrical circuits. Just like an actuator, a relay requires a control signal. A control signal from one circuit, usually an electronic circuit, switches the relay on or off, which in turn switches the electrical circuit on the other side on or off.

This is a schematic of a relay. When a current passes through the relay coil it pulls the switch arm in the main electrical circuit to the open position, switching off the light and when the current through the relay is stopped, the switch is pulled to the closed position by a spring. This is an "always-on" relay. It can also be the reverse, an "always-off" relay so that when a current passes through the relay the main circuit and the connected appliance is switched on and when the current through the relay stops the appliance is switched off.

Thus, digital or analog signals from processors, or even directly from sensors, can act as control signals for a relay and change the state of the electrical machine they are controlling.