Simpler Self-Powered Wireless for Energy-Smart Automation

The buzz around the Internet of Things is highlighting the value of inexpensive and flexible connectivity technologies for general sensing and control. Wireless is the way forward for many applications, such as smart buildings, home automation, industrial control and medical monitoring.

Combining wireless connectivity with energy-harvesting technology in devices such as sensors and switches gives complete freedom, not only from data cabling but also from mains-connected power supplies and batteries.


Self-Powered Switches

Self-powered wireless switches can help simplify installation of lighting controls in homes, offices, hotels, entertainment venues, and also in confined living spaces such as boats or caravans. In addition, older buildings can be modernised with better, safer, energy-saving or LED lighting without requiring invasive rework or detracting from the building’s original character. They can also be used to control air conditioning or motor-driven mechanisms such as vents or window winders.

In any application, installers have the maximum freedom to position switches in the most suitable location, even when a nearby mains supply or wall socket is not available. Since they are self-powered, the switches can operate maintenance-free for extended periods, with no need to replace batteries. And if any units need to be relocated in the future, they can be easily moved to their new position with no rewiring necessary.


Development Kit Simplifies Setup

Configuring and using energy-harvesting wireless switches is now easier than ever with the new AFIK-1002 Wireless Switch Evaluation Kit by Cherry. The kit contains a wireless switch, an energy-harvesting RF generator, a receiver, USB cable for connecting the receiver to a computer, and antennas. In addition to the USB output, the receiver also has a TTL output, a low-voltage relay output, and RS-232 and RS-485 bus outputs, which can be used to control various types of systems.


The kit also includes a manual, and all the necessary drivers and software are available for download from the Cherry website. Together, the kit and software provide everything needed to quickly setup experimental wireless connections or test potential applications using self-powered switches.

Pairing switches with the receiver is easy, requiring little more than to put the receiver in the correct mode and actuate the wireless switch. Cherry’s Radio Monitor development software is easy to use, and provides all the data needed to verify connections and perform range testing. Each time the switch is actuated, an on-screen graphic provides visual confirmation and the software records the unique switch identity, switching state, received signal strength, and received message in a table. The data can be exported as a .tsv file for analysis using Excel.

RS Components is currently the sole source for the evaluation kit. In addition all components are available individually, which allows developers to create bespoke solutions meeting specific end-user requirements. Two types of energy-harvesting switches are available, giving a choice of rocker or snap-type actuator. The full Cherry line-up includes switch and receiver variants designed for operation in 868MHz, 915MHz or 2.4GHz unlicensed (ISM) frequency bands available in various territories worldwide. RS is stocking the 868MHz versions, which can be used throughout Europe.


Peeking Inside

The energy-harvesting RF generator at the heart of Cherry’s self-powered switches is available as a standalone module. This provides the opportunity to incorporate energy harvesting into custom switch designs if required.

The module takes advantage of electromagnetic induction - using coils, a magnet and an energy-management unit - to transform mechanical energy into electrical energy when the user activates the switch. Moving the magnet changes the magnetic flux of the coils, and the energy in the resulting electric impulse is stored in the energy-management unit. An ultra-low-loss converter then delivers the energy, at a predefined supply voltage, to the RF electronics, which sends the radio protocol with all user data via the antenna system to a receiver. The diagram illustrates the main functional blocks of the switch.


Two main systems handle energy conversion and wireless transmission


Actuating and releasing the switch mechanism generates 0.33mWs of energy, which is enough to send three data telegrams. The switches transmit at low power, typically 10-14dBm. When paired with the receiver, which has RF sensitivity of -95dBm, the switches can operate over transmission distances of up to 300 metres in open air, or around 30 metres within a building. The mechanism is designed for a lifetime of at least one million operations.

The high performance and reliability of these switches, combined with Cherry’s development kit, which is easy to use and understand, should make energy-harvesting technology an increasingly popular choice in a growing number of sense and control projects.