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Save Time and Cost in IIoT Facilities with Wireless Energy Harvesting Switches

By Bill Giovino

Contributed By Digi-Key's North American Editors

Advances in the Industrial Internet of Things (IIoT) have translated into increased factory and manufacturing efficiencies due to improved sensor-based monitoring. Improvements in human interface devices such as touchscreens and membrane switches have also helped. Still, there are instances where a mechanical switch is still required for control systems due to their ruggedness and ease of use. Problems can sometimes arise when that switch must be operated some distance away from the equipment being controlled.

These situations include when a forklift truck driver must control an entryway, or when the device to be controlled is normally inaccessible or in an environmentally protected location. In such cases when running wires can be impractical and costly, a wireless switch is a better option. Even then, a wireless switch’s operation is subject to battery life, and so maintenance is required to charge or swap out the battery regularly.

This article will show how batteryless energy harvesting switches from ZF Electronics (formerly Cherry Industrial Solutions) can solve these issues.

IIoT and energy harvesting switch applications

It’s frequently possible to use existing equipment when migrating to an IIoT framework, especially when traditional wall-mounted equipment and light switches are used, and electric power is readily available at these locations. However, many manufacturing facilities are built to be easily configurable so that the present assembly line can be quickly taken down and re-configured to manufacture a different product. Reconfiguration can be costly in terms of downtime, so any technology or solution that can shorten the reconfiguration time should get a second look from designers and plant technicians. Energy harvesting switches are one such time-saving solution.

Most factory machines are networked to the main control hub and can be configured from that central location. However, there are situations where equipment must be operated on the factory floor where it is either impractical or inconvenient, or both, to control the system at the equipment location. Such situations include opening and closing doors remotely, turning high voltage equipment on and off, operating equipment elevators, opening and closing valves, controlling environmentally protected or sensitive equipment or devices, or configuring venting systems. Sometimes the operating switch cannot be mounted in one place and must be mobile, or the available mounting area is glass or concrete and so cannot hold a mounting bracket.

While these are all widely different applications, they all have one thing in common—they are non-standard switch applications where normal mounting, wired connectivity, and maintenance procedures do not apply. For these unusual applications, ZF Electronics has developed wireless, batteryless switches such as the AFIS-5003 energy harvesting rocker switch (Figure 1). The switch is self-contained and maintenance free, requiring no additional components for proper operation.

Image of ZF Electronics AFIS-5003 energy harvesting rocker switchFigure 1: The ZF Electronics AFIS-5003 uses no external power or battery. Instead, it generates the power used to transmit a wireless signal by harvesting the energy generated when the switch is pressed. (Image source: ZF Electronics)

The AFIS-5003 looks like a standard rocker switch and can be mounted in a standard 27 x 12 millimeter (mm) mounting hole. However, instead of two contact mounting tabs on the back, there is a single 70 mm wire extending perpendicular from the switch. This wire is an antenna used to transmit a switch action to a compatible receiver. The switch derives its power by converting the energy generated when the switch is pressed. Depressing one side of the switch requires 1.12 pounds (lb) of force which is harvested by a small internal generator.

The generator outputs a voltage sufficient to momentarily transmit a series of 330 microwatt (µW) 48-bit data packets, referred to as telegrams, that sends the switch’s state to a compatible receiver. The AFIS-5003 transmits over the 915 megahertz (MHz) band, and the telegram is transmitted three times, although the switch can be configured to transmit up to seven telegrams for increased reliability. The delay between each transmitted telegram is pseudo-randomly spaced which helps overcome any periodic RF interference, including other AFIS-5003 switches that might be activated at the same time. Each telegram contains the switch’s unique ID number, switching state, and the total number of telegrams transmitted for that switch actuation.

The AFIS-5003 switch is rated for 100,000 actuations, making it robust enough for frequent use. Operating temperature is -40°C to +85°C so it is suitable for most industrial environments. The switch is IP40 rated so it is protected against some dust, although it is not moisture resistant. For an industrial environment it is recommended that the switch be mounted in a small enclosure. The enclosure should be plastic, as metal would interfere with the transmission of the wireless signal.

Since the switch requires no power, battery charging or replacement is not required, which eliminates a costly maintenance routine. This also assists in troubleshooting if there is a problem receiving the telegrams, as battery life is not a diagnostic issue. In addition, external power does not need to be run to the switch, simplifying factory layout. If necessary, the switch can be easily moved to another location in seconds, instead of scheduling maintenance personnel to relocate the switch and power.

Elevator operation

The switch has two antennas: An internal pc board antenna has a limited range that depends upon both the enclosure and environment. For greater distances, a 2.756 inch wire antenna on the back of the switch is rated to transmit a telegram up to 100 feet. However, ZF Electronics’ own testing has shown that with a clear line-of-sight and minimal interference, these energy harvesting switches can transmit as far as 980 feet.

Like all radio frequency (RF) transmitters, proper placement of the antenna is critical to maximize the effectiveness of the switch. The wire antenna should not be twisted and must not come in contact with any metal surfaces, both of which could limit the antenna’s range.

A practical application for the AFIS-5003 switch would be a forklift elevator. A forklift operator drives into the elevator and then needs to move the elevator between floors. Instead of wasting time getting out of the forklift to operate a wall switch, a ZF Electronics AFIS-5003 switch can be with the forklift operator to enable the elevator. This is especially useful for operations where forklifts from other facilities might be temporarily at the factory location, or other forklifts may be reassigned to other facilities. A plastic box with the AFIS-5003 switch can be temporarily attached to the forklift within easy reach of the operator. Since the switch would only need to transmit inside the elevator, this application could benefit by only using the switch’s internal pc board antenna. This would limit the transmit range, making it less likely to interfere with other switches or nearby devices.

Energy harvesting switch receiver

The switch transmits its signal to a compatible ZF Electronics receiver such as the AFZE-5003 receiver module (Figure 2). A switch transmitter is paired with a receiver by pressing the pairing button on the receiver, then activating the energy harvesting switch. A light flashes on the receiver to indicate it is successfully paired. This receiver can receive signals from up to 32 ZF Electronics energy harvesting 915 MHz transmitters, although this can be increased to 256 transmitters with the manufacturer’s assistance. One energy harvesting switch can be paired with an unlimited number of receivers. Pairing one switch with two or more receivers can be useful in critical applications where redundancy is required, or where switch range must be extended when the same system needs to be controlled from multiple distant locations.

Image of ZF Electronics AFZE-5003 915 MHz receiver moduleFigure 2: The ZF Electronics AFZE-5003 915 MHz receiver module (on right) can receive signals from up to 32 energy harvesting transmitters, and can be extended to up to 256 transmitters. It is also available without the housing as seen on the left. (Image source: ZF Electronics)

The AFZE-5003 can connect to any microcontroller, programmable logic controller (PLC), or computer with a UART interface supporting RS-232 or RS-485 using TTL logic levels. As seen in Figure 2, the AFZE-5003 on the right is in a plastic housing suitable for an industrial environment. It also has a USB 2.0 interface to connect to a host PC for application development. The operational component of the AFZE-5003 is a stamp-sized board as seen on the left (Figure 2, again). This board is also available as a stand-alone unit for integration into a larger system.

The receiver can be powered by the USB interface or an external 5 volt power supply and maintains pairing information even when disconnected from power. The AFZE-5003 can be located near the central PLC where it receives telegrams from all the energy harvesting switches on the factory floor. The switch state is then sent over the UART to the PLC, which then configures the appropriate equipment via Ethernet or Wi-Fi.

Energy harvesting switch development

For development, ZF Electronics supplies the AFIK-5002 energy harvesting evaluation kit (Figure 3).

Image of ZF Electronics AFIK-5002 evaluation kitFigure 3: The ZF Electronics AFIK-5002 evaluation kit contains everything a developer needs to evaluate an energy harvesting switch system including a rocker switch, pushbutton, stand-alone generator, and a receiver. (Image source: ZF Electronics)

The evaluation kit contains the same receiver unit and rocker switch discussed earlier. A USB cable is also included. The plastic antenna housing for the receiver is seen in the middle foreground of Figure 3. The evaluation kit also contains an energy harvesting pushbutton switch as well as a stand-alone energy harvesting generator similar to the ZF Electronics AFIG-0007, seen with a yellow coil in Figure 3. This generator is at the heart of every ZF Electronics energy harvesting pushbutton or rocker switch and is responsible for translating the switch actuation into the transmitted telegram. Developers can use the energy harvesting generator as-is, or they can build their own energy harvesting switch using the generator.

The evaluation kit is easy to use. The receiver is connected by USB to a PC which is running the kit’s demo software. Any or all of the included switches can be paired with the receiver. The demo software shows the status of the pairing operation and also displays all received telegrams including the raw 48-bit telegram data, a timestamp, the switch’s unique ID number, switch state, a count of the number of telegrams transmitted for that switch actuation, and signal strength. The signal strength information is especially important as it greatly helps in ensuring that the distance and placement between transmitter and receiver allows for reliable signal strength.

Conclusion

Energy harvesting switches can solve unique problems in IIoT situations that would seem to have no easy solution. As shown, they can greatly simplify the layout of an industrial facility by providing added flexibility for switch placement in locations where conventional solutions would be impractical.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Bill Giovino

Bill Giovino is an Electronics Engineer with a BSEE from Syracuse University, and is one of the few people to successfully jump from design engineer, to field applications engineer, to technology marketing.

For over 25 years Bill has enjoyed promoting new technologies in front of technical and non-technical audiences alike for many companies including STMicroelectronics, Intel, and Maxim Integrated. While at STMicroelectronics, Bill helped spearhead the company’s early successes in the microcontroller industry. At Infineon Bill orchestrated the company’s first microcontroller design wins in U.S. automotive. As a marketing consultant for his company CPU Technologies, Bill has helped many companies turn underperforming products into success stories.

Bill was an early adopter of the Internet of Things, including putting the first full TCP/IP stack on a microcontroller. Bill is devoted to the message of “Sales Through Education” and the increasing importance of clear, well written communications in promoting products online. He is moderator of the popular LinkedIn Semiconductor Sales & Marketing Group and speaks B2E fluently.

About this publisher

Digi-Key's North American Editors