Relays are humble devices, but they are not immune to being impacted by the Internet of Things. Electromechanical relays, solid-state relays, and MEMs relays are among the numerous devices in the IoT that can connect to the cloud. Some relays include Wi-Fi controllers or Bluetooth, some use power over Ethernet (PoE), and others use voice controls, but each has IP connectivity to reach the cloud. Basic relays can be used to control power flow. Smart relays with IP connectivity can also monitor, measure, and report power flow and other operational and environmental parameters of connected devices in smart buildings, communications systems, and Industry 4.0 facilities.
Electromechanical relays are available that include integrated web servers. These IP-based relays are designed for applications ranging from security systems to pump and motor control, lighting controls, and other smart building systems like heating, ventilation, and air conditioning (HVAC). They can be accessed set up through a standard web browser and piggyback on an existing wireless network for optional cloud connectivity. Automated control can be implemented using programable logic controllers (PLCs) or industrial computers that can read XML status pages from the relay or by using the Modbus/TCP protocol (Figure 1). There’s also an optically isolated input for simpler control functions.
These IP relays can be configured to operate without being connected to a computer. In this direct connection mode, a control signal from one IP relay can be used to control a second IP relay at a remote location that’s an arbitrary distance away by connecting through the cloud. This feature has several applications:
- A large industrial facility’s output from a PLC can be connected to an IP relay. That IP relay can be used to communicate with a second IP relay at a remote location to control other devices in the facility across an IP network (Figure 2).
- While each IP relay has only a single connection, it’s possible to connect multiple IP relays in a daisy-chain configuration where the first IP relay controls a second IP relay that’s connected in turn to a third IP relay, and so on for the required number of connections and controls.
- For remote monitoring and security applications, the remote IP relay can be connected to a sensor to monitor various environmental parameters or the opening and closing of doors, gates, windows, and so on. The IP connection to a second relay can activate an alert about the changing conditions at the remote location.
Wi-Fi relays with up to 28-mile range.
Another type of smart relay uses Wi-Fi for IoT and cloud connectivity. Wi-Fi is available with solid-state relays for low to moderate power switching and electromechanical relays for applications requiring higher power switching. These relays have firmware that supports the control of one or more relays with automatic commands or manual control. The Wi-Fi control module can be connected to any PC to set up the network and control the attached relay. Each Wi-Fi controller is matched with a dedicated relay board. All communications are secure and encrypted based on a unique encryption key to ensure that a controller board and relay board communicate with each other (Figure 3).
Wi-Fi controlled relays are available with single pole double throw (SPDT) configurations rated for 5, 10, and 20 A, a single pole single throw (SPST) configuration rated for 30 A, and double pole double throw (DPDT) configurations rated for 1, 3, and 5 A. And while these Wi-Fi relays can be used in smart buildings, they also support extended communications ranges for outdoor communications. They have a range of up to 2,000 feet in indoor or urban environments using integrated antennas. Adding external 2.1dB dipole antennas can extend the range up to 9 miles for line-of-sight applications. Exchanging the 2.1dB dipoles for high-gain antennas can extend the line of sight range up to 28 miles.
Because of their long-distance capabilities, Wi-Fi relays can be much lower in cost to deploy for remote control of gates, lighting systems, pumps, and motors compared with wired solutions that can require extensive trenching and wiring. These Wi-Fi relays have two primary modes of operation:
In beacon mode, the relay communicates with its controller many times per second in beacon mode and refreshes the relay status information. If the connection is interrupted, the ready LED on the controller stays on, and the relay will stay in its current state.
In smart mode, the relay communicates with the controller any time a change is detected. Otherwise, the controller periodically checks to ensure the relay is still connected. Smart mode also verifies that the relay on the remote device is set correctly. If communications are lost between the relay and controller, the relay will automatically shut off within 30 seconds.
Smart relays for smart homes
Smart relays using Wi-Fi and Bluetooth can be integrated into smart appliances or smart outlets or used to retrofit and upgrade existing installations. These smart relays are small enough to fit into many existing electrical outlets, converting a dumb outlet into a smart controller (Figure 4).
These microcontroller-based smart relays support numerous functions:
- Remote control using mobile apps that can be programmed for one or multiple appliances and functions.
- Voice control through a smart speaker connected to a service like Amazon Alexa or Google Assistant.
- Multiple control channels use relays with up to four input channels that control four independent power outputs.
- Time-based functions
- Devices like lights can be programmed to turn on or off at specific times during the day.
- A cycle timer can be used for cyclic on/off functions like turning a light on for a defined period every day.
- A random timer can turn devices on and off at random times and for random durations. In addition, the user can set a window of time during the day during which the random on/off functions will occur.
- Electricity statistics and protection functions. These MCU-based relays can constantly monitor the voltage, current, and power consumption and provide real-time and historical data reporting. Users can set overcurrent, overvoltage, and overload points, and the relay will be automatically disconnected when the set value is exceeded.
PoE, IP, and relays
Smart relays are available that have integrated PoE and IP connectivity. These relays are designed to control security cameras, modems, controllers, and other devices on an Ethernet network. They operate from 48 Vdc and can provide outputs from 5 to 24 Vdc and 15.4 W of power. An integrated IP connection can be used to control non-PoE devices. These smart relays monitor the operation of the connected device and can be programmed to automatically reboot the device if it locks up. They connect to the cloud, mobile phone handsets, and another device through a computer or network switch with PoE capability. Features of these rack-mountable PoE relays include:
- 10/100Mbps fast Ethernet
- 4 x 100Mbps Auto-MDIX PoE ports
- Automatically detects the PoE class level of powered devices
- Power-saving technology powers down unused ports, and when a connected device is in standby mode
- Switch can auto reboot POE devices based on connectivity
- One user configurable general purpose relay output
- Integrated web interface
Summary
Smart MCU-controlled relays are an integral part of the IoT. They use various connectivity technologies like Wi-Fi, Bluetooth, PoE, and even voice commands combined with IP connectivity to provide smart power control and energy management. Cloud connectivity further enhances the utility of these highly capable relays in smart buildings and Industry 4.0 applications.
References
Electrical relay ratings, Omron
PoE Relays, uSwitch
WebRelay users manual, Xytronix Research & Design
Wi-Fi relay switch smart solution, tuya
Wireless Contact Closure 1-Way Transmitter Receiver Pair, National Control Devices
