Back to basics: An introduction to electromechanical switches

Electronic Products launches its back to basics electronic component series, in partnership with EDN, with an introduction to electromechanical switches. Don’t miss our discussion with Roger Bohannan, global segment leader for C&K’s medical segment product portfolio.

Selecting the right electromechanical switch for an application can be challenging. From shock/vibration and size requirements to tactile feel and performance demands, integrating the right switch into a product can make or break a design. Below is an electromechanical switch overview, providing the core information you need to understand typical switch types, common applications, and often used terms related to switches.

Often referred to as electronic or electrical switches, electromechanical switches are available in many different types (for example slide, toggle, pushbutton, etc.), a variety of current switching capabilities, and physical sizes to support a range of functions. Offering reliable and durable operation for simple and complex tasks, electromechanical switches use mechanical action to change the state of an electrical device by altering the electrical flow through different circuit transmission paths.

Commonly used in human-to-machine interfaces (HMI), electromechanical switches are a relatively low-cost and simple solution when compared to other forms of HMI and are, therefore, a preferred choice by many designers. It’s easy selecting an electromechanical switch for your application, but optimizing your switch choice to maximize your design functionality and your customer’s experience of your product is where the switch manufacturer’s expertise can help you.

Here is a list of popular types of electromechanical switches. These switches are typically specified by several parameters: actuator type, number of poles and throws, level of sealing, actuation force, haptic feedback and power rating required.

 Tactile switches

A “tact” switch is an electromechanical device, but essentially a machine interface. With its momentary action, the switch is ON only for the period it is pressed and goes OFF as soon as it is released. When the device is actuated, the metal dome acting as a mobile contact collapses between the two stationary contacts and generates the electrical switching, providing a signal from the circuit to electronic control unit (ECU) or microcontroller (MCU) of the equipment.

As its name suggests, “tact” switches provide different haptics. Four main criteria are perceived by the user: tactile feeling, actuation travel, actuation force, and actuation sound. The combination and the control of these parameters determine the ideal applications in which a switch can be used. To achieve custom haptics, the actuators, domes, and housings can be mixed-and-matched in order to obtain the right look, feel, and performance.

These switches are offered in a broad range of different sizes for printed-circuit-board (PCB) mounting. Available in illuminated, side or top actuated, sealed or unsealed, silver or gold contact material, SMT and through-hole versions, tact switches can be tuned to any application requirements.

Modern tact switches can withstand a minimum of 10 million cycles, making them perfect for high usage applications such as game controllers or elevator interface controls. This performance is the result of the right combination of a soft actuator and a revised internal structure made of the housing and the dome which is the heart of the switch. The product design also ensures a high sealing level. An IP67 rating offers strong protection against dust and water ingress.

Miniature versions are now available for consumer and wearable products like hearing aids. With a small footprint, rugged nano tact switches are easy to integrate and offer designers the freedom to either add more functionality or reduce the size of the end product.

Roger Bohannan, global segment leader for C&K’s medical segment product portfolio discusses key trends in the portable and connected medical device market and how they impact electromechanical switch design – Gina Roos, editor-in-chief, Electronic Products.

 

Keyswitches

A keyswitch is an electromechanical device that utilizes a spring and a cam to optimize the switch’s haptic feedback for the user’s experience. An alternative to tactile or pushbutton switches, a keyswitch is typically used only for low current or signal applications.

Keyswitches are recognizable underneath each key of a mechanical joystick, control grip, electrosurgical instrument, or keyboard. These switches have a wide range of actuation force, electrical circuit, travel, and illumination, which make them attractive to automotive, medical, industrial, and off-road designers.

It is important that keyswitches exhibit excellent haptics. In applications involving an array of keyswitches, consistent actuation force and feel help determine the quality of the end product. Keyswitches can be directly actuated using either their own, often built-in button or cap, or through a customer’s own interface such as a rubber membrane or cover.

Keyswitches for modern applications must be designed for long-term, high-performance operation in standard and environmentally-demanding applications.

Many keyswitches designed for harsh environments offer waterproof sealing. Keyswitches with a unique design that separates electrical and mechanical functions ensure accurate switching positions and can withstand up to 100 N overload and 1 M actuations. Keyswitches are available in a wide range of color illumination options to accommodate specific customer application requirements.

DIP switches

A dip switch comes with terminals configured in a standard dual-in-line package.  A simple DIP comes in a rectangular housing with two parallel rows of electrical connecting pins.  The package may be either through-hole mounted or surface-mounted to the PCB.

There are many different kinds of DIP switches. The most common are the slide, piano, and rotary types. The slide and piano types are typically arranged in single-pole/single-throw (SPST) contacts, which can be either on or off. The rotary types contain multiple electrical contacts, one of which is selected by rotating the switch to align it with a number printed on the package.

DIP switches are still used in some remote controls to prevent interference. For example, to control a ceiling fan (and its light fixture) that is retrofitted to a single-circuit junction box. DIP switches set a different radio frequency or address for each transmitter/receiver pair, so that multiple units can be installed without unintentionally controlling each other.

Snap-action switches

A snap-action switch detects (or senses) the presence or absence of an object as well as its position by activating a plunger when the object physically comes in contact. With a snap-action mechanism, the contacts will instantaneously switch at a specific operating position regardless of its speed. The mechanism allows the snap switch to operate using a specified movement and force.

Today with the advent of the internet of things (IoT), snap-action switches have been widely adopted for position detection applications, including home appliances, machines, and mechanical-electrical equipment. Electrical signals outputted from the snap switch indicates normal and abnormal conditions when detecting positions, which can be transmitted through the internet and used as preventive maintenance and remote monitoring.

Snaps are solid products. They range from low to high current and potentially can withstand any water splashes up to IP67 rating. They can be used in a wide range of applications, including industrial, automotive, consumer, and medical.

Modern snap-action switches offer significant customization options, which is particularly important for the automotive market. Rated to IP67, automotive snap-action switches are available with different actuator and termination options, short or long travel, silent operation or with a click, and more.

Detect switches

Detect switches work in the same way as a snap-action switch. The size of a detect is much smaller than a snap-action switch due to the evolution of switch technology, and it is typically used only for low current or signal applications. Due to its small size, detect switches tend to be used in small footprint IoT devices, ranging from tobacco heating systems and drug delivery devices to smoke alarms, Bluetooth audio devices, and 4K cameras.

Detect switches are typically surface mounted on PCBs. It offers a shorter travel than snap-action switches due to a smaller body. However, it is well suited for extremely small, constrained spaces where snap-action switches cannot fit into the application.

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Pushbutton switches

Pushbutton switches feature a button actuator that closes and opens the switch and is used to control some aspect of a machine or a process. The pushbuttons are typically constructed of plastic or metal. The cap or actuator’s surface is usually flat or shaped to accommodate the human finger or hand, so as to be easily depressed or pushed.

Pushbutton switches offer the longest travels for HMI applications, as buttons require a spring in the internal structure to return to its open state. With built-in overtravel, these switches can be used with a mechanical interface and prevent the switches from being over-actuated and possibly damaged.

Designed for both power and logic-level applications in the same size housing, pushbutton switches meet the engineers concept of “one size fits all” requirement. Also, pushbutton switches can accommodate several circuits with multiple several poles and throws in a single body, which increase the functionality in devices or equipment. Pushbuttons are available with or without LEDs as lighted indicators and various termination styles like panel or PCB mounting with vertical or right-angle configurations. To meet demanding requirements in harsh conditions or hazardous environments, the products often provide industry-standard ingress protection (IP) and impact protection (IK).

Pushbutton switches are commonly selected for their tamper-proof design. An IP67-rated design guarantees survival in dusty and wet conditions, while an IK10 rated actuator with a stainless steel or aluminum alloy housing ensures high resilience to vandalism. Pushbuttons provide versatility with a range of options, including momentary or lock versions, LED indicators in a variety of colors, and as well as several actuator choices.

Rocker switches

A rocker switch is an electrical on/off switch that rocks from one side to the other when pressed to change the switch state, either connecting or disconnecting an electrical circuit. Rocker switches come in a variety of flavors, such as subminiature, miniature, and power, providing an extensive range for PCB through-hole, surface mount, and panel mount applications. Models are available in illuminated (LED and incandescent) and sealed/waterproof versions, with SPST, SPDT, DPST, DPDT, 3PDT, and 4DPT functionality.

PCB mount options include vertical, right angle, and surface mount, while panel mount options include front mount, rear mount and snap-in versions. With multi-pole, multi-position functionality, rocker switches can be used in a variety of applications.

Rocker switches can come with momentary and maintained functions, optional guards to prevent accidental actuation, and an IP54 splashproof rubber boot option.

Toggle switches

A toggle switch is an electrical switch that opens and closes an electrical circuit by moving a lever back and forth.  Available in single pole up to four poles, toggle switches are offered in a wide range of versions, including low-voltage miniature, subminiature, and ultra-miniature models, and up to high power 20-A devices. With PCB, SMT, and bushing options, toggle switches feature vertical, right angle, and vertical right-angle mounting bracket versions.

Toggle switches offer a wide range of actuation forces, electrical circuits, and travel, which makes them attractive for control panels, telecommunications instrumentation, medical equipment, heavy equipment, industrial instruments, lifts & escalators, security systems, LED light and detection applications. They also can be designed into harsh environment applications with typical IP68-rated sealing.

Navigation

Navigation switches typically incorporate multiple axes of travel with a long lever arm in products like thumbsticks, four-way direction switches, and other similar products. These devices can be miniaturized to fit within a wide range of applications including mirror controls in automotive, white goods, consumer electronics, entertainment systems, and remote controls.

As an example, thumbsticks can combine dual-axis lever controls with integrated center-select switching. This unique design meets the reliability requirements demanded by premium controller products such as high-end commercial drones, gaming peripherals, and industrial controllers.

Slides

Slide switches are identified by their horizontally sliding actuator, which opens or closes the switch. These types of switches come in all shapes and sizes from ultra-miniature to larger, high power models. They can also incorporate multiple switch functions, from the basic single pull/single throw (SPST) to SPDT, SP3T, DPST, DPDT, 3PDT, 4PDT, and 4P3T functions.

They can also be constructed for various installation methods, including surface mount, panel mount, PCB through-hole, or right-angle variants. Further customization options, depending on the application, include positive detent, sealing, and shorting or non-shorting contacts.

Slide switches are easy to integrate into a design and give engineers more design flexibility and options for size, mounting styles, actuation types, ratings, and packages. Many miniature slide switches are now compliant with the latest UL61058-1 standard. These devices can be used in a variety of applications, such as consumer electronics, HVAC controls, audio equipment, and security systems.

Rotary

Rotary switches provide rotational actuation, often with 4, 8, 12, or even 16 positions evenly spaced around the circular housing. They can be quite tiny in order to fit into small applications or made a little larger in order to accommodate higher power loads. It’s possible to incorporate multiple poles based on the number of positions that the rotary switch offers, including both shorting and non-shorting contacts. Rotary switches are well suited for automotive applications, appliances, industrial equipment, medical equipment, consumer electronics, and anywhere a rotating dial is required to control functionality.

Switchlocks

Switchlocks combine electrical switching contacts with keyed security lock mechanisms in applications where secure switching is critical. Switchlocks are offered in multi-pole and multi-position options, positive detent, and can operate at a low power level.

These switches are constructed of either plastic or metal housings and use four to six tumblers to support a variety of security needs. They can incorporate anti-static and momentary functions as needed with bushing or snap-in mounting options to meet a wide range of applications including point-of-sale terminals, cash registers, computers, networking equipment, vending machines, elevators, medical equipment, and security systems.

Conclusion

Switches ultimately shape the end-user experience. Electromechanical switches come in a wide range of shapes, sizes, actuators, materials, and termination options to meet application demands, and each of these choices effect the feel, the sound, and the response to the user as the product is actuated. By selecting the right electromechanical switch your product design can be elevated and used to enhance your end user’s experience. From standard illuminated switches to sealed switches and switches that mount on the surface, or custom miniature switches with a broad range of operating forces and lever styles, switches can make or break the success of  your product.

Common Terms Actuation force: The force required to change a switch actuator from one position to another. Measured exactly when a switch changes state. Mechanical travel: The stroke (movement of the actuator) from the initial position to the mechanical stop. Electrical travel: Stroke from the initial position to the electrical contact. Tactile effect: The difference between the actuation force and the force at the mechanical stop position. Haptic: A combination of the actuation force, sound, travel, and tactile effect. Overload: The maximum force applicable on the switch without damage. Life expectancy: The number of cycles of operation that a switch will perform. UL/ENEC: Global standards for safety. Actuator: A movable part of a switch that causes a change in the electrical configuration of the switch. Actuation: Operating or releasing a switch by depressing or releasing its actuator or rotating its shaft. Alternate action: A pushbutton switch style in which the electrical state of the switch is maintained between actuations of the plunger. Contact resistance: The junction resistance between two contacts, typically measured at the contact terminals. It is the total resistance based on the construction and film resistances. Make: Indicates that a switch has closed an electrical circuit. Make & break contacts: Contacts that make/break current flow. They are differentiated from those that operate principally in a sliding mode. Make-before-break: The moving contact establishes a new circuit before interrupting the circuit previously established, while transferring to another position. Non-shorting contacts: Break-before-make. Shorting contacts: Make-before-break. Referred to rotary and slide switches. Normally closed: Contacts that touch each other and establish a circuit when in their  normal position. Normally open: Contacts that do not touch and interrupt the circuit when in their normal position.